access xiv programthe applicant's thesis or postdoctoral research must be in the field of...

ACCESSXIV

FOURTEENTHATMOSPHERICCHEMISTRYCOLLOQUIUMFOREMERGINGSENIOR

SCIENTISTS

July27-30,2017BrookhavenNationalLaboratory

Upton,NY

PROGRAM

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Table of Contents

Table of Contents ............................................................................................................................ 3 Title Page ......................................................................................................................................... 5 ACCESS XIV PARTICIPANTS ..................................................................................................... 7 Representatives from Federal Agencies .......................................................................................... 9 Representatives from the Gordon Research Conference in Atmospheric Chemistry ................... 10 ACCESS Chairs ............................................................................................................................. 10 Representatives from Supporting Organizations ........................................................................... 11 Former ACCESS Participants in Attendance ................................................................................ 12 Administrative Support ................................................................................................................. 12 ACCESS ........................................................................................................................................ 13 History of ACCESS ....................................................................................................................... 14 ACCESS Sponsors – Major Federal Agencies .............................................................................. 15 ACCESS Sponsors – Other Organizations .................................................................................... 17 Brookhaven National Laboratory .................................................................................................. 21 Long Island .................................................................................................................................... 22 ACCESS XIV Agenda .................................................................................................................. 23 ACCESS XIV Abstracts ................................................................................................................ 29

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ACCESSXIV


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JointlySponsoredby:U.S.DepartmentofEnergy(DOE)

NationalAeronauticsandSpaceAdministration(NASA)NationalOceanicandAtmosphericAdministration(NOAA)

NationalScienceFoundation(NSF)U.S.EnvironmentalProtectionAgency(EPA)

WithAdditionalSupportfrom:

BrookhavenScienceAssociates(BSA)CarnegieMellonUniversity(CMU)DepartmentofChemistry

AerodyneResearch,Inc.TofwerkAG

CaliforniaAirResourcesBoard(CARB)DropletMeasurementTechnologies(DMT)

NationalCenterforAtmosphericResearch(NCAR)AerosolDynamics,Inc.andAerosolDevices,Inc.

HandixScientific

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ACCESS XIV PARTICIPANTS

Kelvin Bates, Harvard University, [email protected]

Thomas Berkemeier, Georgia Institute of Technology, [email protected]

Yvonne Boose, Karlsruhe Institute of Technology, [email protected]

Hallie Boyer, Carnegie Mellon University, [email protected]

Ewan Crosbie, NASA Langley Research Center, [email protected]

Jennifer Faust, College of Wooster, [email protected]

Meng Gao, Harvard University, [email protected]

Lauren Garofalo, Colorado State University, [email protected]

Jack Kodros, Colorado State University, [email protected]

Louise Kristensen, University of California at San Diego, [email protected]

Pengfei Liu, Harvard University, [email protected]

Christina McCluskey, Colorado State University, [email protected]

Brett B. Palm, University of Colorado at Boulder, [email protected]

Sarah Petters, University of North Carolina at Chapel Hill, [email protected]

Paul Romer, University of California at Berkeley, [email protected]

Provat Saha, Carnegie Mellon University, [email protected]

Emily Saunders, Howard University, [email protected]

Ryan Sullivan, Cornell University, [email protected]

Kang Sun, Harvard-Smithsonian Center for Astrophysics, [email protected]

Alex Turner, University of California at Berkeley, [email protected]

Wendell Walters, Brown University, [email protected]

Chen Wang, University of Toronto, [email protected]

Megan Willis, University of Toronto, [email protected]

Lu Xu, California Institute of Technology, [email protected]

Yue Zhang, University of North Carolina at Chapel Hill, [email protected]

Ernie R. Lewis, Brookhaven National Laboratory, ACCESS Chair

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Representatives from Federal Agencies Dr. Shaima Nasiri Atmospheric System Research Program Manager, DOE Program Management U.S. Department of Energy Climate and Environmental Sciences Division SC-23.1, Germantown Building 1000 Independence Avenue, SW Washington, DC 20585-1290 [email protected] 301-903-0207 Dr. Ken Jucks Program Manager, Upper Atmosphere Research Program (UARP) Earth Science Division NASA Headquarters 300 E Street SW Washington, DC 20546-0001 [email protected] 202-358-0476 Dr. Ken Mooney Program Manager: Atmospheric Chemistry, Carbon Cycle, & Climate (AC4) NOAA Climate Program Office 1315 East West Highway, 12th Floor Silver Spring, MD 20910 [email protected] 301-734-1242 Dr. Sylvia A. Edgerton Program Director: Atmospheric Chemistry Division of Atmospheric and Geospace Sciences National Science Foundation 4201 Wilson Boulevard Arlington, VA 22230 [email protected] 703-292-8522 Dr. Sherri W. Hunt, ACCESS VII Assistant Center Director: Air, Climate and Energy National Center for Environmental Research USEPA Headquarters Ariel Rios Building 1200 Pennsylvania Avenue, N. W. Washington DC, 20460 [email protected] 202-564-4486

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Representatives from the Gordon Research Conference in Atmospheric Chemistry

Dr. Kim Prather, 2017 GRC Chair Distinguished Chair in Atmospheric Chemistry Department of Chemistry & Biochemistry University of California at San Diego 9500 Gilman Dr. La Jolla, CA 92093 [email protected] 858-822-5312 Dr. Ron Cohen, 2017 GRC Vice-Chair, ACCESS II Professor of Chemistry and of Earth and Planetary Sciences Department of Chemistry B68 Hildebrand University of California Berkeley, CA 94720-1460 [email protected] 510-642-2735 Dr. Neil Donahue, 2017 GRC Vice-Chair Professor of Chemical Engineering, Chemistry, and Engineering and Public Policy Doherty Hall 2116 Carnegie Mellon University 5000 Forbes Avenue Pittsburgh, PA 15213 [email protected] 412-268-4415

ACCESS Chairs Ernie R. Lewis, ACCESS Chair Atmospheric Scientist Biological, Environmental & Climate Sciences Department Brookhaven National Laboratory Building 815E Upton, NY 11973-5000 [email protected] 631-344-7406 Dr. Lenny Newman, ACCESS Chair Emeritus Brookhaven National Laboratory Bldg 815E Upton, NY 11973-5000 [email protected]

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Representatives from Supporting Organizations Dr. Martin Schoonen Associate Laboratory Director Environment, Biology, Nuclear Science, and Nonproliferation Directorate Brookhaven National Laboratory PO Box 5000 Upton, NY 11973-5000 [email protected] 631-344-4014 Dr. Alexis Attwood Director of Business Development Droplet Measurement Technologies 2400 Trade Centre Avenue Boulder, CO 80503 [email protected] 720-633-8799 Dr. David Edwards Associate Director, National Center for Atmospheric Research ACOM Administrative Office PO Box 3000 Boulder, CO 80307-3000 [email protected] 303-497-1857 Ms. Pat Keady President Aerosol Devices, Inc. 2614 S. Timberline Rd. #109-125 Fort Collins, CO 80525 [email protected] 970-744-3244 Dr. Gavin McMeeking, ACCESS X Senior Scientist Handix Scientific LLC 5485 Conestoga Court Suite 104-B Boulder, CO 80301 [email protected] 720-724-7658

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Former ACCESS Participants in Attendance Dr. Laura Fierce, ACCESS XIII Environmental and Climate Sciences Department Brookhaven National Laboratory Building 815E Upton, NY 11973-5000 [email protected] 631-344-6084 Dr. Chongai Kuang, ACCESS X Environmental and Climate Sciences Department Brookhaven National Laboratory Building 815E Upton, NY 11973-5000 [email protected] 631-344-7257 Dr. Jian Wang, ACCESS VII Environmental and Climate Sciences Department Brookhaven National Laboratory Building 815E Upton, NY 11973-5000 [email protected] 631-344-7920

Administrative Support Adrienne Jerry Brookhaven National Laboratory Building 490D Upton, NY 11973-5000 [email protected] 631-344-7525 Nancy Barci Brookhaven National Laboratory Building 815E Upton, NY 11973-5000 [email protected] 631-344-7548 Sharon Zuhoski Brookhaven National Laboratory Building 815E Upton, NY 11973-5000 [email protected] 631-344-3359

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ACCESS Atmospheric Chemistry Colloquium for Emerging Senior Scientists

The purpose of ACCESS is to bring together young researchers in atmospheric chemistry and

representatives of the principal federal government agencies that fund atmospheric chemistry

research to engage in scientific discussion and interaction. The meetings will forge future

professional relationships, and the entire atmospheric science community will benefit by becoming

more aware of innovations in atmospheric chemistry through presentations by ACCESS

participants and through these interactions. ACCESS is held every other year (since 1991) in

conjunction with the Gordon Research Conference (GRC) in Atmospheric Chemistry.

To be eligible to participate in ACCESS, an applicant must have received a doctorate from an

accredited university no more than two years before the colloquium, or provide certification that in

all probability he/she will have received a doctorate degree in less than one year after the

colloquium. The applicant's thesis or postdoctoral research must be in the field of atmospheric

chemistry. Attendance at ACCESS is limited to 25 participants, who are selected by a committee

based on the significance and achievement of the applicant’s thesis or postdoctoral research, the

application, and a letter of recommendation from the applicant’s major thesis or postdoctoral

advisor. Participation in ACCESS is highly competitive, as there are typically nearly 100

candidates, coming from the most prestigious institutions in the US and abroad.

Participation in ACCESS and GRC is jointly sponsored by the U.S. Department of Energy (DOE),

National Aeronautics and Space Administration (NASA), the National Oceanic and Atmospheric

Administration (NOAA), the National Science Foundation (NSF), and the U.S. Environmental

Protection Agency (EPA). Additional support is provided by Brookhaven Science Associates

(BSA), Carnegie Mellon University (CMU) Department of Chemistry, Aerodyne Research, Inc.,

TOFWERK AG, the California Air Resources Board (CARB), Droplet Measurement Technologies

(DMT), the National Center for Atmospheric Research (NCAR), Aerosol Dynamics, Inc. and

Aerosol Devices, Inc., and Handix Scientific. We thank these organizations for their support!

Please address questions or comments to Ernie Lewis, ACCESS Chair, at [email protected].

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History of ACCESS

The following is from an email from Chuck Kolb to Ernie Lewis (2011-08-03) in response to a

request for information on how ACCESS started.

The idea came up when I was chairing the National Research Council/National Academy of Science Committee on Atmospheric Chemistry. In 1990 Tom Gradel told me about DISCO, an oceanographic community program that organized a workshop for new PhD recipients focused on meeting their peers and jointly learning about their field’s research traditions and opportunities from senior oceanographers. He suggested that atmospheric chemistry would benefit from a similar program. I presented the idea to the NRC/NAS committee which endorsed it. I decided to tie a meeting for young atmospheric chemists to the next Atmospheric Chemistry Gordon Conference. As co-chairs of the 1991 Atmospheric Chemistry Gordon Conference, Mario Molina and I accepted the challenge of organizing both meetings. I took the idea to Jarvis Moyers, atmospheric chemistry program manager at NSF, to explore with him how we could shape the concept and get it funded. Bolstered by his guidance and enthusiastic response, we organized the first Atmospheric Chemistry Colloquium for Emerging Senior Scientist (ACCESS). Funding was provided by NSF, NASA, DOE and NOAA. I provided the program, which included research presentations by each participant to their peers and presentations by and discussions with funding agency representatives. I also provided the acronym. After the 2.5 day (Thursday/Friday/Saturday am) ACCESS meeting held at MIT, on Sunday we bussed the participants to New Hampshire for their first Gordon Conference.

Thanks to Chuck for the information and for starting ACCESS!

Year ACCESS ACCESS Chairs GRC Chairs Location 1991 I C. Kolb M. Molina and C. Kolb MIT 1993 II J. Logan D. Golden and M. Prather Harvard 1995 III L. Newman and S. Schwartz L. Newman and S. Schwartz BNL 1997 IV D. Worsnop and P. Davidovits D. Jacob and P. Wine Boston College 1999 V J. Merrill and B. Heikes W. Brune and J. Penner U. Rhode Island 2001 VI L. Newman S. Sander BNL 2003 VII L. Newman B. Finlayson-Pitts Yellowstone NP 2005 VIII L. Newman D. Fahey Yellowstone NP 2007 IX L. Newman D. Worsnop Yellowstone NP 2009 X L. Newman P. Wennberg BNL 2011 XI L. Newman K. Boering and J. Abbatt BNL 2013 XII E. Lewis S. Brown and Y. Rudich BNL 2015 XIII E. Lewis P. Shepson BNL 2017 XIV E. Lewis K. Prather BNL

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ACCESS Sponsors – Major Federal Agencies Participation in ACCESS and GRC is jointly sponsored by the U.S. Department of Energy (DOE), National Aeronautics and Space Administration (NASA), the National Oceanic and Atmospheric Administration (NOAA), the National Science Foundation (NSF), and the U.S. Environmental Protection Agency (EPA).

We thank these agencies for their support! U.S. Department of Energy's Atmospheric System Research (ASR) Program http://asr.science.energy.gov/ The U.S. Department of Energy’s Atmospheric System Research program advances process-level understanding of the key interactions among aerosols, clouds, precipitation, radiation, dynamics, and thermodynamics, with the ultimate goal of reducing the uncertainty in global and regional climate simulations and projections.

DOE is represented at ACCESS XIV by Dr. Shaima Nasiri.

National Aeronautics and Space Administration's Science Earth Program http://science.nasa.gov/earth-science The National Aeronautics and Space Administration (NASA) conducts a program of breakthrough research to advance fundamental knowledge on the most important scientific questions about the global integrated Earth system using space-based observations.

NASA is represented at ACCESS XIV by Dr. Ken Jucks.

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National Oceanic and Atmospheric Administration's Atmospheric Chemistry, Carbon Cycle, & Climate (AC4) Program http://cpo.noaa.gov/ClimatePrograms/EarthSystemScience/AtmosphericChemistryCarbonCycleandClimate.aspx The National Oceanic and Atmospheric Administration's AC4 Program aims to provide a process-level understanding of the climate system through observation, modeling, analysis, and field studies to support the development and improvement of models and ultimately predictions.

NOAA is represented at ACCESS XIV by Dr. Ken Mooney.

National Science Foundation's Atmospheric Chemistry Program https://www.nsf.gov/funding/pgm_summ.jsp?pims_id=11692 The National Science Foundation's Atmospheric Chemistry Program supports research to measure and model the concentration and distribution of gases in the lower and middle atmosphere.

NSF is represented at ACCESS XIV by Dr. Sylvia Edgerton.

U.S. Environmental Protection Agency's Air Research Program http://www2.epa.gov/air-research The U.S. Environmental Protection Agency (EPA) conducts research that provides the critical science to develop and implement Clean Air Act regulations that protect the quality of the air that we breathe.

EPA is represented at ACCESS XIV by Dr. Sherri Hunt.

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ACCESS Sponsors – Other Organizations Brookhaven Science Associates (BSA) www.bsa-hq.org/ Brookhaven Science Associates is a partnership between Stony Brook University and Battelle that manages Brookhaven National Laboratory on behalf of the U.S. Department of Energy.

Brookhaven Science Associates is represented at ACCESS XIV by Dr. Martin Schoonen.

Carnegie Mellon University (CMU) Department of Chemistry http://www.cmu.edu The Department of Chemistry at Carnegie Mellon University conducts exciting research programs that often use interdisciplinary approaches to bring insight to important problems, particularly at the interface areas related to nanotechnology and biotechnology.

The CMU Department of Chemistry is represented at ACCESS XIV by Dr. Neil Donahue.

Aerodyne Research, Inc. http://www.aerodyne.com/ Aerodyne Research provides research and development services and advanced instrument and software products to industrial, academic and government customers addressing national and international environmental, energy and defense challenges.

We thank Dr. Doug Worsnop and Aerodyne Research for their support.

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Tofwerk AG www.tofwerk.com/ Tofwerk is a Swiss company that offers custom instrumentation for research laboratories and OEM partners, and high performance end-user instruments.

We thank Dr. Katrin Fuhrer and Dr. Marc Gonin of Tofwerk for their support.

California Air Resources Board (CARB) www.arb.ca.gov/homepage.htm The California Air Resources Board promotes and protects public health, welfare and ecological resources through the effective and efficient reduction of air pollutants.

We thank Bart Croes and CARB for their support.

Droplet Measurement Technologies (DMT) www.dropletmeasurement.com Droplet Measurement Technologies manufactures cutting-edge instruments for measuring water droplets, ice crystals, CCN, ozone, black carbon, bioaerosols, and other aerosols.

Droplet Measurement Technologies is represented at ACCESS XIV by Dr. Alexis Attwood.

National Center for Atmospheric Research (NCAR) https://ncar.ucar.edu The National Center for Atmospheric Research is a federally funded research and development center devoted to service, research and education in the atmospheric and related sciences.

NCAR is represented at ACCESS XIV by Dr. David Edwards.

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Aerosol Dynamics, Inc. and Aerosol Devices, Inc. www.aerosol.us and aerosoldevices.com Aerosol Dynamics specializes in the measurement of airborne particles, with the goal of developing better methods and instrumentation for characterizing atmospheric aerosols. Aerosol Devices brings to the market advanced aerosol collector technology developed by Aerosol Dynamics.

Aerosol Dynamics and Aerosol Devices are represented at ACCESS XIV by Ms. Pat Keady. We additionally thank Dr. Susanne Hering and Aerosol Dynamics for their support.

Handix Scientific www.handixscientific.com Handix Scientific is a research and development company focusing on atmospheric aerosol.

Handix is represented at ACCESS XIV by Dr. Gavin McMeeking.

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Brookhaven National Laboratory

ACCESS XIV is convened at Brookhaven National Laboratory (BNL), one of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy. BNL’s mission is to advance fundamental research in nuclear and particle physics to gain a deeper understanding of matter, energy, space, and time; apply photon sciences and nanomaterials research to energy challenges of critical importance to the nation; and perform cross-disciplinary research on climate change, sustainable energy, and Earth’s ecosystems. BNL is a multipurpose research institution and operates cutting-edge large-scale facilities for studies in physics, chemistry, biology, medicine, applied science, and a wide range of advanced technologies. It applies world-class facilities and expertise to the most exciting and important questions in basic and applied science—from the birth of our universe to the sustainable energy technology of tomorrow. BNL is operated and managed by Brookhaven Science Associates, (BSA) which was founded by the Research Foundation for the State University of New York on behalf of Stony Brook University, and Battelle, a nonprofit applied science and technology organization. The Laboratory's almost 3,000 scientists, engineers, and support staff are joined each year by more than 4,000 visiting researchers from around the world. Our award-winning history stretches back to 1947, and we continue to unravel mysteries from the nanoscale to the cosmic scale, and everything in between. Opened in 1947 on the former site of the U.S. military’s Camp Upton, Brookhaven National Lab’s initial mission centered on the peaceful exploration of the atom. Particle accelerators, leading chemistry and biology experiments, and a host of visionary scientists soon joined groundbreaking research reactors, and Brookhaven began endless innovations and explorations. Our scientists have discovered subatomic particles, new forms of matter, and pioneered the kinds of technology that fuel leading experimental programs all over the world. Our research has also led to life-saving medical imaging techniques that have revolutionized diagnosis and treatment of disease. Brookhaven research has been honored by seven Nobel Prizes, as well as National Medals of Science, Enrico Fermi Awards, Wolf Foundation Prizes, dozens of R&D 100 awards, and many other recognitions. The Lab offers extensive research and education opportunities for elementary school students through post-doctoral fellows, as well as professional development programs for teachers. The Long Island Solar Farm, located at Brookhaven, is the largest solar photovoltaic power plant in the Eastern U.S. Dr. Doon Gibbs currently serves as Laboratory Director.

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Long Island

Brookhaven National Laboratory (BNL) is located on Long Island in New York State. Long Island extends more than 100 miles eastward from New York City and is just over 20 miles across (north to south) at its widest point. Two boroughs of New York City, Brooklyn and Queens, are geographically located on Long Island; however, these are not typically considered part of Long Island by locals. Long Island is bordered on the south by the Atlantic Ocean and on the North by Long Island Sound, which separates Long Island from Connecticut, roughly a dozen miles away. The population of Long Island is nearly 8 million, and its population density is greater than that of any state. However, much of the area near BNL and eastward is wooded and rural. The Peconic Bay, which starts roughly a dozen miles east of BNL, splits eastern Long Island into two forks, the South Fork and the North Fork. The South Fork is known for the Hamptons, hangout of celebrities and rich New Yorkers. Montauk Lighthouse, on the eastern tip of the South Fork, was commissioned by the U.S. Congress in 1792 under George Washington, and is the fourth oldest active lighthouse in the U.S. Southampton, the oldest town on the South Fork, dates from 1640. The North Fork has a very New England feel, and consists of farms and more than four dozen wineries, including the one at which the banquet will be held. Its oldest settlement, Southold, also dates from 1640.

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ACCESSXIV


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AGENDA

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ACCESS XIV Fourteenth Atmospheric Chemistry Colloquium for Emerging Senior Scientists

July 27-30, 2017

BROOKHAVEN NATIONAL LABORATORY All Sessions are in Room Berkner B

Thursday, July 27 Light dinner (Hampton Inn, 2000 N. Ocean Ave., Farmingdale, NY) ..................... 6:00-10:00 pm Friday, July 28 Pick up at Hampton Inn for BNL .......................................................................................... 7:30 am Registration and check-in at BNL ............................................................................... 8:00-8:30 am

SESSION I: INTRODUCTORY REMARKS AND WELCOME ................. 8:30-9:00 am chaired by Ernie Lewis, BNL

Ernie Lewis, ACCESS Chair, Brookhaven National Laboratory Martin Schoonen, Associate Laboratory Director for the Environment, Biology,

Nuclear Science, & Nonproliferation Directorate, BNL Doon Gibbs, Laboratory Director, Brookhaven National Laboratory Shaima Nasiri, Atmospheric System Research Program Director,

US Department of Energy SESSION II: ACCESS PRESENTATIONS (laboratory studies) ............... 9:00-10:40 am

chaired by Sylvia Edgerton, NSF Kelvin H. Bates, Isoprene Oxidation Mechanisms and Secondary Organic Aerosol

Formation Under HO2-Dominated Conditions Thomas Berkemeier, The Role of Phase State and Reactive Intermediates in the

Multiphase Chemistry of Atmospheric Aerosols Hallie C. Boyer, Surface Tension Modeling of Atmospheric Aqueous Aerosols Using

Adsorption Isotherms and Statistical Mechanics Jennifer A. Faust, Influence of Aerosol Liquid Water on the Formation and Composition

of Secondary Organic Aerosol Pengfei Liu, Highly Viscous States Affect the Browning of Organic Particulate Matter

Break ........................................................................................................................ 10:40-11:00 am

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SESSION III: ACCESS PRESENTATIONS (laboratory studies) .... 11:00 am-12:20 pm chaired by Ken Mooney, NOAA

Sarah Suda Petters, Temperature- and Humidity-Dependent Phase States of Secondary Organic Aerosols

Wendell Walters, Constraining Ammonia Emission Sources in Urban Areas Utilizing Nitrogen Stable Isotopes

Chen Wang, The Effect of Different Atmospherically Relevant Salts on Aqueous Phase Partitioning of Organic Compounds

Yue Zhang, The Effects of Aerosol Phase State on Secondary Organic Aerosol Formation from the Acid-Catalyzed Reactive Uptake of Isoprene-Derived Epoxydiols

Lunch (Berkner Room A) ........................................................................................... 12:20-1:00 pm Group Photograph (Berkner Room B) ........................................................................ 1:00-1:15 pm TOUR OF BROOKHAVEN NATIONAL LABORATORY ............................... 1:15-2:45 pm

SESSION IV: ACCESS PRESENTATIONS (field studies) ......................... 3:00-5:00 pm chaired by Ken Jucks, NASA

Yvonne Boose, Using Cellular Network Backhaul Links for Rain Measurements in Africa Ewan Crosbie, Design and Testing of a New Aircraft Cloud Water Sampling Inlet Lauren Garofalo, Measurements of 14CO2 in the Stratosphere and Free Troposphere:

Vertical Profiles and Empirical Radiocarbon Production Rates Louise Jane Kristensen, Investigating the Aerosols Seeding California’s Clouds:

Insights from CalWater2015 Christina McCluskey, Abundance and Characteristics of Marine Ice Nucleating Particles:

Implications for High Latitude Aerosol-Cloud Interactions Brett B. Palm, Development and Application of an Oxidation Flow Reactor to Study

Secondary Organic Aerosol Formation from Ambient Air Pick up at Berkner for banquet ............................................................................................ 5:15 pm BANQUET (Jason's Vineyard, 1785 Main Rd., Jamesport, NY) .............................. 6:00-9:00 pm Pick up, return to Hampton Inn ............................................................................................ 9:00 pm

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Saturday, July 29 Pick up at Hampton Inn for BNL .......................................................................................... 7:30 am

SESSION V: ACCESS PRESENTATIONS (field studies) ............................ 8:00-9:40 am chaired by Shaima Nasiri, DOE

Paul Romer, Effects of Organic Nitrate Chemistry and Temperature-Dependent NOx Emissions on Continental Ozone Production

Provat K. Saha, Secondary Organic Aerosol Formation From In-Situ Oxidation of Near-highway Air

Kang Sun, Constraining Atmospheric Ammonia Emissions through Novel Observations Megan D. Willis, Evidence for Marine Biogenic Influence on the Composition and Growth

of Summertime Arctic Aerosol Lu Xu, Large Contributions from Biogenic Carbon to Organic Aerosol in the Southeastern

United States Break ...................................... ....................... ........................................................... 9:40-10:00 am

SESSION VI: ACCESS PRESENTATIONS (modeling studies) ....... 10:00 am-11:40 pm chaired by Sherri Hunt, EPA

Meng Gao, Improving Understanding of Haze Pollution in the North China Plain via Atmospheric Modeling and Data Assimilation

John K. Kodros, Climate and Health Impacts of Aerosol Emissions from Residential Combustion Sources in Developing Countries

Emily Saunders, Modeling Regional & Global Atmospheric Chemistry Mechanisms - Observing Adverse Respiratory Health Effects due to Tropospheric Ozone Air Pollution from Modeling Output

Ryan Sullivan, New Particle Formation Leads to Cloud Dimming Alexander J. Turner, Ambiguity in the Causes for Decadal Trends in Atmospheric

Methane and Hydroxyl

Final comments (Ernie Lewis) .......................................................................................... 11:40 am ADJOURN ............................ ....................... ................................................................... 12:00 pm Pick up box lunches, take bus to Hampton Inn .................................................................. 12:00 pm Pick up at Hampton Inn for NYC ....................................................................................... 12:45 pm New York City ........................................................................................................ 2:00-10:00 pm Pick up in NYC, return to Hampton Inn ............................................................................. 10:00 pm

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Sunday, July 30 Pick up at Hampton Inn for GRC ......................................................................................... 7:30 am Ferry from Pt. Jefferson, NY to Bridgeport, CT ................................................................... 9:00 am Lunch (CT) ................................................................................................... 12:00 noon – 1:00 pm Arrive at Grand Summit Hotel at Sunday River, Newry, ME ...................................... 5:30 pm

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ABSTRACTS

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Isoprene Oxidation Mechanisms and Secondary Organic Aerosol Formation Under HO2-Dominated Conditions

Kelvin H. Bates

Harvard University Isoprene, a volatile hydrocarbon emitted by plants, represents the single most abundant

source of non-methane organic carbon to the atmosphere. After its rapid oxidation by OH radicals in the troposphere, isoprene may follow any of a number of complex reaction mechanisms to form more highly functionalized products, depending in large part on the relative abundance of reactive radicals such as HO2 and NO; some of these products can be sufficiently water-soluble, non-volatile, and/or reactive to partition into atmospheric particles and contribute to the creation of secondary organic aerosol (SOA). In this work, I explore the gas-phase oxidation mechanisms and SOA formation potential of second- and later-generation products formed in the HO2-dominated reaction cascade, which predominates in remote regions and is estimated to account for >40% of isoprene oxidation. Pure standards of significant isoprene products, such as isoprene epoxydiols (IEPOX) and C4 dihydroxycarbonyl compounds, are synthesized, and the rates and product yields of their gas-phase reactions with OH are measured by CF3O- chemical ionization mass spectrometry in environmental chamber experiments. Results are compared to field observations from the Southern Oxidant and Aerosol Study in the Southeastern United States, where significant concentrations of these compounds were detected, and are integrated into a global chemical transport model to investigate their effects throughout the atmosphere. Further, the results from these and other gas-phase kinetic and product studies are incorporated into an explicit isoprene oxidation mechanism, designed to simulate the effects of isoprene chemistry on oxidant concentrations and to produce accurate representations of products known to be involved in condensed phase processes, including IEPOX. Finally, additional chamber experiments with synthetic IEPOX and inorganic seed aerosol are performed to derive particle uptake coefficients and examine the effects of particle pH, liquid water content, and chemical composition on IEPOX-SOA formation, using aerosol mass spectrometry and differential mobility analysis. The gas- and particle-phase reaction rates and product yields discussed herein, along with the explicit model, provide important constraints on the fate of isoprene-derived carbon in the atmosphere and on the influence the HO2-dominated isoprene oxidation pathway exerts on SOA and oxidant budgets.

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The Role of Phase State and Reactive Intermediates in the Multiphase Chemistry of Atmospheric Aerosols

Thomas Berkemeier

Georgia Institute of Technology Atmospheric aerosols play a key role in climate, air quality and public health, as they enable the formation of clouds and precipitation, reduce visibility and cause adverse health effects upon inhalation. The phase state of organic aerosols ranges from liquid to glassy solid under atmospheric conditions, which affects the rates of various processes during their life cycle. Heterogeneous and multiphase reactions of ozone are important pathways for chemical ageing of atmospheric organic aerosols.

To demonstrate and quantify particle phase state can affect the gas uptake and chemical transformation of organic matter, we apply the kinetic multi-layer model KM-SUB to a comprehensive experimental data set of ozone uptake by various alkenes, namely shikimic acid, tannic acid and oleic acid. We use a newly developed global optimization method, the Monte Carlo Genetic Algorithm (MCGA), to constrain parameters such as reaction rate coefficients, diffusion coefficients and Henry's law solubility coefficients. Shikimic acid, a polysubstituted cyclohexene derivative, is chosen to mimic the diffusion behavior of an important subclass of atmospheric aerosols: secondary organic aerosol (SOA). Bulk diffusion coefficients in shikimic acid were determined to be 10-12 cm2 s-1 for ozone diffusion and 10-20 cm2 s-1 for self-diffusion under dry conditions, but were found to increase by several orders of magnitude with increasing relative humidity (RH), which is consistent with previous studies on SOA. This finding can be explained by particles undergoing moisture-induced phase changes from amorphous solid over semisolid to liquid over the range of atmospherically relevant RH.

Consequently, the reactive uptake of ozone progresses through different kinetic regimes characterized by specific limiting processes and parameters. At high RH, ozone uptake is driven by reaction throughout the particle bulk; at low RH it is restricted to reaction near the particle surface and kinetically limited by slow diffusion and replenishment of unreacted organic molecules. Slow diffusion and ozone destruction can effectively shield reactive organic molecules in the particle bulk from degradation. Our analysis of multiple reactions systems uniformly suggests that the chemical reaction mechanism involves long-lived reactive oxygen intermediates, likely primary ozonides or O atoms, which may provide a pathway for self-reaction and catalytic destruction of ozone at the surface.

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Using Cellular Network Backhaul Links for Rain Measurements in Africa

Yvonne Boose Karlsruhe Institute of Technology (KIT), Campus Alpin, Garmisch-Partenkirchen, Germany

Flash floods and droughts cause major hazards to the population and economy of Sub-Saharan West African countries. Early warning systems and appropriate water management could ease some of the impact. However, early warning requires accurate quantitative precipitation estimation (QPE) in real-time. Only three radar systems exist in West Africa which provide this type of data for Southern Mali. At the same time, the number of available rain gauge measurements is declining worldwide, also in West Africa. A recent promising method is to derive rain rates from the attenuation of microwaves between cellular network base stations, so-called commercial microwave links (CMLs). With a rapidly increasing number of cellphone users, the CML network in West Africa is growing in coverage and density, thus providing a high potential for CML-derived precipitation measurements.

The relationship of attenuation to rain rate is quasi-linear for typical CML bandwidths (10 - 40 GHz). However, also humidity, dust, water on the antennas, or electronic noise can lead to signal interference. To distinguish these fluctuations from actual attenuation due to rain, a temporal wet (rain event occurred)/ dry (no rain event occurred) classification is necessary prior to rain rate retrieval. In dense CML networks this is possible by correlating neighboring CML signals. Another option is to use time series analysis, based either on the standard deviation of the attenuation or its Fourier transform. The CML network in rural areas in West Africa is typically not dense enough for correlation analysis and the attenuation signal is noisier than in Europe. Thus, I follow a different approach and study how cloud information from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) radiometer onboard the geostationary satellite METEOSAT can be used for a wet/dry classification in Burkina Faso and Germany. This presentation will show results for CML-based QPE in Germany and first steps of applying the method in Burkina Faso.

First results show that simple METEOSAT-derived criteria such as cloud cover and cloud top temperature perform worse than time series analysis in Germany but better in Burkina Faso. Higher level METEOSAT products like the precipitation rate yield a higher probability of detection (POD = 51%) and a slightly lower false alarm ratio (FAR = 24%) of rain events than the standard deviation time series analysis (POD = 24%, FAR = 27%) for CMLs in Germany. These results show that a combination of geostationary satellite and CML-derived precipitation data can yield improved precipitation rate information compared to the single products. In a next step, this will be tested also for Burkina Faso. Other satellite data, such as the IMERG precipitation product of the recently launched Global Precipitation Measurement mission, may be more accurate in rain rate retrieval, but their temporal resolution and timely availability are lower compared to METEOSAT. As such they are less applicable for near real-time applications, but will be compared to the CML-data for validation purposes.

34

Surface Tension Modeling of Atmospheric Aqueous Aerosols Using Adsorption Isotherms and Statistical Mechanics

Hallie C. Boyer

Carnegie Mellon University Surface properties of atmospheric aerosol particles are crucial for accurate assessment of

the fates of liquid particles in the atmosphere. Surface tension directly influences predictions of aerosol particle activation to clouds through the Kelvin effect, as well as indirectly acts as a proxy for chemical surface partitioning. Chemical species residing on aerosol particle surfaces influence particle interactions with the vapor phase, including associated growth processes and heterogeneous chemistry. However, atmospheric aerosols typically comprise complex mixtures of chemical compounds with varied surface effects. The chemical complexity of aerosol microenvironments challenges comprehensive thermodynamic treatment of aerosol particles. Considering the significance of aerosol surfaces to particle properties and processes in the atmosphere, this work explores aqueous aerosol interfaces through thermodynamic modeling of surface tension. Using adsorption isotherms and statistically mechanically derived expressions for entropy and Gibbs free energy, surface tensions are predicted as functions of concentration. Single solute and multicomponent aqueous solutions are treated containing surface-active organics, inorganic electrolytes, and mixtures. A unique feature of the model is the surface partition function, where the solvent molecules (waters) represent adsorption sites, and solute molecules can displace multiple waters either positively or negatively, depending on the level of surface activity of the solute. For binary solutions, model parameters are eliminated through correlations with solute properties, such as molar volume for organics and surface-bulk partitioning coefficients for electrolytes. A multicomponent model is derived for an arbitrary number of solutes, using no further parametrization beyond the optimized binary cases. For organic and inorganic aqueous mixtures, model predictions agree excellently with available data, including measurements at supersaturated concentrations using optical tweezers. Ultimately, improved understanding of aerosol particle surfaces would enhance treatment of aerosol particle-to-cloud activation states and aerosol effects on climate.

35

Design and Testing of a New Aircraft Cloud Water Sampling Inlet

Ewan Crosbie NASA Langley Research Center/Universities Space Research Association

Clouds are an integral component of Earth’s climate system. In addition to their familiar role in the hydrologic cycle, clouds also strongly influence the radiation budget in both the shortwave and longwave, serve as an important conduit in the fate and emergence of trace chemical species in the atmosphere, and affect the lifetime and properties of aerosols. The chemical composition of cloud droplets is determined by a combination of the aerosol particles that initially act as their nuclei, dissolved gases, and mixing processes associated with entrained airmasses. The abundance of chemical species in cloud water is affected by aqueous reactions that require accurate representation in atmospheric models, yet there is a dearth of observational constraints on these processes, particularly for organic compounds. Cloud processes result in downstream impacts on gas-phase concentrations and the physical and chemical properties of residual aerosol particles. Aircraft-based sampling of cloud water for chemical analysis poses many challenges not faced by ground-based techniques at mountaintop sites. However, by default an aircraft is the only feasible platform able to collect cloud water samples in most scenarios. In an unpressurized cabin, cloud water samples have been collected for several decades using a Mohnen slotted rod, which employs a similar principal to gravity-driven cloud water collection techniques at mountain sites. This technique is unsuitable for pressurized aircraft, which comprise the majority of NASA’s Earth Science research fleet. In this presentation, I will discuss the design, testing, implementation, and flight performance of a cloud water sampling inlet which uses centrifugal separation of cloud water from the airstream in an axial cyclone. The current design, known as AC3 (axial cyclone cloud-water collector), results in a ten-fold increase in cloud water collection efficiency compared to a previous design. The AC3 has been used during a recent field deployment of the North Atlantic Aerosol and Marine Ecosystems Study (NAAMES) on board the NASA C-130. At the time of writing, the probe is being upgraded in preparation for the next deployment of NAAMES. During July-August 2016, the probe was operated in tandem with the Mohnen Slotted Rod collector on board the Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter as part of the Fog and Stratocumulus Evolution (FASE) field campaign, which targeted California stratocumulus. Using the two cloud water collectors, 156 concurrent samples spanning fifteen flights were analyzed for major inorganic ions, organics, metals, and absorption spectra from 260-700 nm. While some variability occurred on individual samples, campaign mean and flight mean concentration of most major species agreed within 20%. Sea salt comprised the major fraction of the marine cloud water composition by mass, however the region was also extensively affected by the Soberanes Fire. At least four of the flights were substantially influenced by the fire plume and there was clear evidence of entrainment of the plume into the marine stratocumulus cloud, observed through enhanced gas and aerosol concentrations and chemical markers of the fire in the cloud water composition. The cloud water also exhibited enhanced absorption in the dissolved phase with a spectral signature corresponding to brown carbon.

36

Influence of Aerosol Liquid Water on the Formation and Composition of Secondary Organic Aerosol

Jennifer A. Faust

College of Wooster Aerosol droplets present a unique aqueous reaction medium in the atmosphere because of their small volume and high concentrations of both inorganic and organic solutes. Secondary organic aerosol (SOA) can form when volatile organic compounds (VOCs) are oxidized to yield semivolatile species, which then condense onto atmospheric seed particles and partition into the aqueous phase according to physical solubility. Most commonly, dissolution is driven by processes like hydration; other reactions within the condensed phase also enhance overall uptake.

Here we examine effects of aerosol liquid water (ALW) on relative SOA yield and composition from α-pinene ozonolysis and the photooxidation of toluene and acetylene by OH. Reactions were conducted in a room-temperature flow tube under low NOx conditions in the presence of equivalent loadings of wet (~20 µg m-3 ALW) or dry (~0.2 µg m-3 ALW) ammonium sulfate seeds at exactly the same relative humidity (RH = 70%) and state of wall conditioning. We found 13% and 19% enhancements in relative SOA yield for the α-pinene and toluene systems, respectively, when seeds were wet rather than dry. The relative yield doubled in the acetylene system, and this enhancement was partially reversible upon drying the prepared SOA, which reduced the yield by 40% within a timescale of seconds. We attribute the high relative yield of acetylene SOA on deliquesced seeds to aqueous partitioning and particle-phase reactions of its photooxidation product glyoxal. Overall, we conclude that particle-phase water mediates SOA formation in the atmosphere, but the extent of its influence varies widely according to VOC precursor.

37

Improving Understanding of Haze Pollution in the North China Plain via Atmospheric Modeling and Data Assimilation

Meng Gao

Harvard University

Frequent haze events have been happening in the North China Plain (NCP), and the severity of these events has attracted massive attention from both the public and the scientific community. Extremely high aerosol loadings in these haze events significantly influence visibility, human health and climate. Thus, improving understanding of haze pollution is of great importance. Furthermore, air quality modeling remains challenging. We elucidated the roles of meteorology, secondary aerosol formation, regional transport, and aerosol feedbacks in winter haze formation, clarified the impacts of emission changes and meteorology changes on PM2.5 concentrations, directly emphasized the importance of implementing pollution control strategies using assessments of health and climate effects, and improved model performance in simulating sulfate and PM2.5 via incorporating heterogeneous sulfate formation and assimilating surface PM2.5 concentrations. These results provide some implications for policy makers. Priorities should be given to control SO2, NH3, and OC emissions, which can be achieved by promoting the shift from coal/biofuel to cleaner energy, and by changing animal feeding and housing ways. In addition, more attention to greenhouse gases and absorbing aerosols is still necessary since absorbing aerosols play important roles in aerosol feedbacks, aerosol feedbacks can aggravate haze pollution, and increases in temperature may increase aerosol concentrations. To protect the public health, it is of great importance to predict air pollution episodes, release alerts of incoming severe haze episodes, and take emergency measures to reduce pollution levels.

38

Measurements of 14CO2 in the Stratosphere and Free Troposphere: Vertical Profiles and Empirical Radiocarbon Production Rates

Lauren Garofalo

Colorado State University The radiocarbon (14C) content of various carbon-containing species including CO2 has long

been used to quantify inventories, residence times, and gross fluxes of carbon in and between the atmosphere, biosphere, and oceans, as well as to study large-scale atmospheric transport. Now that the large influx of radiocarbon injected into the stratosphere by the atmospheric nuclear weapons tests in the mid-twentieth century has been purged from the stratosphere, the spatial and temporal distribution of Δ14CO2 in the stratosphere is determined by natural cosmogenic production, transport, and stratosphere-troposphere exchange including the propagation of radiocarbon-free fossil fuel combustion products into the stratosphere. Here, I will present an extensive dataset of recent Δ14CO2 measurements from samples collected in the troposphere and lower stratosphere, and describe an empirical method to estimate the global annual mean net isotope fluxes of Δ14CO2 from the stratosphere to the troposphere. These measurements and analyses provide much needed constraints on the spatial and temporal distribution of 14CO2 necessary to monitor the stratospheric circulation and stratospheric residence times, quantify the partitioning of carbon between the atmosphere, biosphere, and oceans, and infer regional and global fossil fuel emissions from the large number of Δ14CO2 measurements made at Earth’s surface.

Measurements of Δ14CO2 were performed on 150 whole air samples collected by NASA aircraft (ER-2, DC-8, and WB-57) from flight campaigns in 1997, 2000, 2004, 2012, and 2013 spanning a varying range of latitudes in the Northern Hemisphere, as well as 59 whole air samples collected during high-altitude balloon flights in 2003-2005 at 34oN. In these vertical profiles, Δ14CO2 generally increases with increasing altitude, as expected for a tracer with a stratospheric source (cosmogenic production in the upper troposphere/lower stratosphere) combined with a 14C-depleted source of CO2 at the surface (fossil fuel combustion). The correlations between Δ14CO2 and N2O mixing ratios in the stratosphere are used to estimate global annual mean net 14CO2 fluxes between the stratosphere and the troposphere, which are approximately half of the global 14C cosmogenic production rates. To within the uncertainties, these isotope fluxes have not changed between 1997 and 2013, suggesting that the stratospheric age spectra are likely wide enough to damp out variations in the 14C production rate caused by the 11-year solar cycle. A lack of dependence on the solar cycle simplifies the use of stratospheric Δ14CO2 measurements as a tracer of stratospheric transport to detect and monitor possible changes in the stratospheric circulation and residence times due to increases in radiative forcing from greenhouse gases, as well as to quantify the transport of 14CO2 from the stratosphere to the troposphere which is necessary for carbon cycle studies.

39

Climate and Health Impacts of Aerosol Emissions from Residential Combustion Sources in Developing Countries

John K. Kodros

Colorado State University Globally, close to 2.8 billion people lack access to clean cooking technology, while 1.8 billion people lack access to electricity altogether. As a means to generate energy for residential tasks, it is common in many developing countries to rely on combustion of solid fuels (wood, dung, charcoal, trash, etc.) for residential tasks. Solid fuel use (SFU) can emit substantial amounts of PM2.5 often in close proximity to residences, creating concerns for human health and climate. This work estimates these health and radiative forcing impacts of residential SFU (e.g. cooking, heating, lighting) and the combustion of domestic waste (i.e. trash burning). Using a global chemical-transport model, GEOS-Chem, with an online aerosol microphysics model, TOMAS, we quantified the sensitivity of the aerosol direct radiative effect (DRE) and aerosol indirect effect (AIE) from residential SFU due to uncertainties in emission and model parameters. The sign and magnitude of the global-mean DRE (−20 to +60 mW m-2) is strongly sensitive to the black carbon to organic aerosol emission ratio, the absorptive properties of OA (termed “brown carbon”), and assumptions on how BC is mixed with scattering particles, while the AIE (+10 to −20 mW m-2) is strongly sensitive to the emission size distribution. Aerosol emissions from SFU have been estimated to have substantial health impacts; however, the uncertainties in mortality estimates (such as from the Global Burden of Disease Study) have not been quantified. We perform a variance-based sensitivity analysis on mortality attributed to the combined exposure to ambient and household PM2.5 from SFU to determine what factors lead to uncertainties in mortality estimates. We find that uncertainty in the percent of the population using solid fuels for energy contributes the most to the uncertainty in mortality (50-60% of uncertainty across Asia and 40-50% in South America) with the concentration-response function the next largest contributor (40-50%). Conversely, the ambient and personal PM2.5 exposure contributes little to the estimated variance in mortality estimates (1-7%). Thus, we recommend future studies should focus on more precise quantification of population using solid fuels as well as exposure-response relationships to PM2.5. Using a similar global modeling approach, we made the first estimates of the DRE and AIE from uncontrolled combustion of domestic waste. Owing to uncertainties regarding aerosol optical properties as well as emission mass and size distributions, we estimated the globally averaged DRE to range from -40 mW m-2 to +4 mW m-2 and the AIE to range from -4 mW m-2 to -49 mW m-2. We estimated exposure to ambient PM2.5 from domestic-waste combustion to cause 270,000 adult mortalities per year, most of which occur in developing countries. Overall, the aerosol radiative effects from SFU and trash combustion are largely uncertain and can range between positive and negative. Conversely, while there are still major uncertainties in global mortality estimates, the global health burden of this emission sector is substantial, providing a strong motivation for improvement in developing countries.

40

Investigating the Aerosols Seeding California’s Clouds: Insights from CalWater2015

Louise Jane Kristensen

University of California at San Diego

The severity of California’s droughts increases the need to identify aerosols that suppress or enhance precipitation within California. Precipitation is influenced strongly by the aerosols that serve as cloud condensation nuclei (CCN) and ice nucleating particles (INP). Changes to precipitation patterns may be the result of changes to the source and type of aerosols responsible for seeding clouds. Investigation into aerosol impacts on clouds and precipitation in California’s Sierra Nevada as part of the CalWater field campaigns showed increased dust and biological aerosols in precipitation and cloud residues during increased.

The aim of the CalWater2015 field campaign was to investigate the extent different types of aerosols and their sources influence precipitation efficiency, particularly on Atmospheric Rivers. Between January and March 2015, 27 research flights were conducted onboard the Department of Energy Gulfstream 1 measuring the aerosols found in California’s ambient air and cloud ice and droplet residuals. Five of these flights took place during the occurrence of a significant Atmospheric River between February 5th to 8th 2015. An Aircraft Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) was used to characterize and identify in situ single particles within clouds acting as ice and cloud nuclei. Aerosol types were identified from unique or combinations of ion markers generated from the ATOFMS.

To elucidate changes in aerosol species and source, potentially affecting precipitation, the local ambient aerosol composition of California was established. The aerosol species consistently present in California’s ambient air from urban and agricultural emissions include predominantly of carbonaceous species such as biomass burning, soot, organic carbon and highly processed sulfate and nitrate aerosols. Sea salt aerosols were also consistently present in aerosol populations due to California’s coastal location. Despite the consistent presence of these aerosols readily available to serve as CCN, in cloud residual aerosol populations these aerosols were found in reduced proportions relative to ambient air populations.

Further to the reduced population of local California aerosols measured in cloud residues above California, a significant reduction in these carbonaceous aerosols was also measured on flights encountering an Atmospheric River. Compositions of the main type of aerosol measured by ATOFMS during the February 2015 Atmospheric River show high mass organic carbon (HMOC) oligomerised particles internally mixed with salt and biological particles. Ion markers indicative of biological aerosols (PO3

-, PO2-, CNO- and CN-) were enhanced in the aerosols during the most

intense precipitation period. Contrastingly to previous studies, no dust aerosols were measured during the Atmospheric River.

41

Highly Viscous States Affect the Browning of Organic Particulate Matter

Pengfei Liu Harvard University

Initially transparent organic particulate matter (PM) can become shades of light-absorbing

brown via particle-phase chemical reactions. The production of nitrogen-containing compounds is one important pathway for browning. Semisolid or solid physical states of organic PM might, however, sufficiently slow the diffusion of reactant molecules to inhibit browning reactions. Herein, organic PM of secondary organic material derived from toluene was exposed to ammonia at different values of relative humidity (RH) from <5% to 90% at 293 K. The production of light-absorbing organonitrogen species from ammonia exposure depended strongly on the RH value. The production of organonitrogen species was kinetically inhibited for RH < 20%. As the RH increased from <20% to >60%, absorption index (k) at 280-320 nm increased by 50% and k at 380-420 nm increased by 400%, indicating ammonia uptake and PM browning. The observed RH-dependent behavior was well captured by a model that considers diffusivities of both large organic molecules that made up the PM and the small ammonia molecules taken up from the gas phase. Large-molecule diffusivity was calculated based on observed SOM viscosity and evaporation. Small-molecule diffusivity was represented by water diffusivity measured in this study, given the similarities between ammonia and water in molecular weight and hydrogen bonding. The approach was to observe rates of water mass uptake or release and to use these rates to calculate diffusivities of the evaporating species. At RH < 20%, although the physical mixing timescale of small molecules can be short in typical sized aerosol particles (0.1 to 10 s for 100 nm particles), fast browning reactions can be kinetically limited because of a shallow diffuse-reactive length. Diffusivity of large organic molecules can be 4-6 orders of magnitude smaller than the diffusivity of small molecules, which further inhibited the refresh process of reactants near the surface. The results of this study have implications for accurate modeling of atmospheric brown carbon production and associated influences on energy balance.

42

Abundance and Characteristics of Marine Ice Nucleating Particles: Implications for High Latitude Aerosol-Cloud Interactions

Christina McCluskey Colorado State University

Concentrations of ice nucleating particles (INPs), particles required for freezing supercooled liquid water (SLW) droplets, and subsequent ice phase transitions are poorly constrained in models. Specifically, satellite observations indicate that clouds over remote oceans have high SLW contents that are not represented in global climate models, leading to large modeled energy biases. Global transport modeling studies suggest that sea spray aerosol is an important contributor to INP populations over remote oceans, due to a link between ocean phytoplankton blooms and ocean-derived INPs. However, little is known regarding the abundance, composition and production of marine INPs. The objective of this project was to 1) determine the natural abundances of marine INPs and 2) confirm the hypothesized increase in marine INP emissions associated with marine organic aerosol that arises from elevated oceanic biological productivity. Natural marine INPs were measured during a series of field campaigns in remote oceans and coastal sites, including the Mace Head Research Station (MHD, west coast of Ireland) and onboard the R/V Investigator during the Clouds, Aerosols, Precipitation, Radiation, and atmospheric Composition Over the southeRn ocean (CAPRICORN, south of Australia). The primary immersion-freezing ice nucleation measurement technique used for these studies is the CSU Ice Spectrometer (IS), an offline measurement of INP number concentrations (nINP) as a function of temperature. During the MHD study, pristine marine aerosol was isolated from the total aerosol using a clean sector sampler and aerosol composition was measured using an aerosol mass spectrometer. The CSU Continuous Flow Diffusion Chamber was also used in the immersion-freezing mode for online detection of nINP (T = -22 to -32 °C) during CAPRICORN. The contribution of heat-labile (e.g., proteins) and organic constituents to the INP population was investigated by performing heating and peroxide digestion treatments to aerosol samples. In pristine marine air masses at MHD, an order of magnitude increase in nINP (active at -15 °C) was observed during periods of elevated marine organic aerosol arising from offshore biological productivity, suggesting that marine INPs are important contributors to the remote INP population at MHD. Relatively high amounts of terrestrial organic aerosol lead to the highest nINP observed during the study period. These trends remain after accounting for aerosol surface area. INPs observed during the marine organic event were heat labile, suggesting the presences of proteinacious INPs. Terrestrial INPs at MHD are likely organic soils, inferred from decreased INP activity due to heating and peroxide digestion treatments. During CAPRICORN, little variability was observed at colder ice activation temperatures, despite variable levels of biological productivity, estimated by Chlorophyll a concentrations (Chl a). Interestingly, increases in heat-labile INPs active at temperatures warmer than -22 °C were observed over regions of elevated Chl a, but these were also located closer to land sources. Overall, nINP observed during CAPRICORN were significantly lower than historical INP surveys. These data provide observations for use in model simulations to evaluate the role of marine INP in remote cloud phase partitioning.

43

Development and Application of an Oxidation Flow Reactor to Study Secondary Organic Aerosol Formation from Ambient Air

Brett B. Palm

University of Colorado at Boulder

Secondary organic aerosols (SOA) in the atmosphere play an important role in air quality, human health, and climate. However, the sources, formation pathways, and fate of SOA are poorly constrained. To address these deficiencies, recent research has focused on the development and application of the oxidation flow reactor (OFR) technique for studying SOA formation from OH, O3, and NO3 oxidation of ambient air. Inside the OFR, the concentration of a chosen oxidant can be increased in order to rapidly form SOA from precursors in sampled air. With a several-minute residence time and a portable design with no inlet, OFRs are particularly well suited for studying SOA formation from ambient air.

This research has contributed to several advances to the performance and interpretation OFR experiments. This includes estimating oxidant exposures, modeling the fate of low-volatility gases in the OFR (wall loss, condensation, and oxidation), and comparing SOA yields of single precursors in the OFR with yields measured in environmental chambers. When these experimental details are carefully considered, SOA formation in an OFR can be more reliably compared with ambient SOA formation processes.

The analysis of field OFR measurements has provided guidance about how SOA is formed in the atmosphere. A comparison of SOA formation from OH, O3, and NO3 oxidation of ambient air in and OFR in a wide variety of environments, from rural forests to urban air, illustrates that OH oxidation can produce substantially more (often 6x) SOA from ambient gas precursors than O3 or NO3 oxidation of the same air. In a rural forest, the measured SOA formation correlated with biogenic precursors (e.g., monoterpenes). In urban air, it correlated instead with reactive anthropogenic tracers (e.g., trimethylbenzene). In mixed-source regions, the SOA formation did not correlate well with any single precursor, but could be predicted by multilinear regression from several precursors. Despite these correlations, the concentrations of speciated ambient VOCs could only explain approximately 10-50% of the total SOA formed from OH oxidation. In contrast, ambient VOCs could explain all of the SOA formation observed from O3 and NO3 oxidation. Evidence suggests that lower-volatility gases (semivolatile and intermediate-volatility organic compounds; S/IVOCs) were present in ambient air and were the likely source of SOA formation that could not be explained by VOCs. These measurements show that S/IVOCs likely play an important intermediary role in ambient SOA formation in all of the sampled locations, from rural forests to urban air.

44

Temperature- and Humidity-Dependent Phase States of Secondary Organic Aerosols

Sarah Suda Petters

University of North Carolina at Chapel Hill

Aerosol particles are abundant in the atmosphere, affecting the water cycle, human health, and the terrestrial radiative balance. It is now known that secondary organic aerosols (SOAs) can exist in amorphous semi-solid or glassy phase states whose viscosity varies with atmospheric temperature and relative humidity (RH). However, the relationships between SOAs, atmospheric conditions, and viscosity are not well known or understood.

In this study I will present SOA amorphous phase state diagrams that show how particle viscosity varies with temperature and RH. Furthermore, I show that the dependence of SOA viscosity on temperature and RH is highly sensitive to composition. SOAs were generated by dark ozonolysis of a series of monoterpenes (α-pinene, Δ3-carene, limonene, myrcene, and ocimene) using a laminar continuous-flow tube reactor. Monodisperse 100 nm aerosol viscosity was measured online at different temperatures and RHs by observing the relaxation of coagulated particles into spheres. Glass transition temperatures were obtained by extrapolating the temperature-dependent viscosity in the range of measurement to 1012 Pa s. Composition was estimated using the fraction of organic mass at m/z 43 (f43) and m/z 44 (f44) using an Aerosol Chemical Speciation Monitor (ACSM).

Results show that the temperature dependence of dry SOA viscosity is similar to that of coal tar pitch, citric acid, and sorbitol. The SOA systems underwent an RH-controlled transition from glassy to semi-solid to liquid between -10 and 30°C. The RH dependence disappears at low temperatures, and the SOAs may be semisolid or glassy at temperatures colder than 10°C and RH less than 100%. For each SOA system the weak dependence of viscosity on RH is likely due to the low hygroscopicity of the particles. Glass transition temperatures for the five SOA systems varied by about 30°C. This range can be explained by subtle changes in functional group composition, molecular structure, or mixing state. To our knowledge this work provides the first direct estimate of SOA glass transition temperatures. Our results suggest that viscosity of SOA systems is highly sensitive to composition. A deeper understanding of the composition dependence of viscosity is needed to better predict the viscosity of organic aerosols and to apply results from the laboratory setting on a global scale. SOA phase state diagrams presented in this work highlight the sensitivity of viscosity to conditions during both the formation and the lifetime of organic aerosols.

45

Effects of Organic Nitrate Chemistry and Temperature-Dependent NOx Emissions on Continental Ozone Production

Paul Romer

University of California at Berkeley Elevated concentrations of tropospheric ozone are an important contributor to anthropogenic radiative forcing and are associated with increased human mortality and decreased crop yields. Observations of increased surface ozone concentrations on hotter days are widely reported, but the mechanisms driving this relationship in rural and remote continental regions are poorly understood. We use observations from the Southern Oxidant and Aerosol Study (SOAS) in summer 2013 at a forested site in the southeast United States, as well as long term monitoring at the same location, to understand nitrogen oxide (NOx) chemistry and ozone production in rural and remote environments. At this location, NOx is oxidized to form alkyl and multifunctional nitrates (ΣRONO2) an order of magnitude faster than it is directly oxidized to form nitric acid. ΣRONO2 at this location are found to be short-lived and nearly half undergo heterogeneous hydrolysis to produce nitric acid.

We use these new observational constraints on NOx chemistry to understand how ozone production is affected by day-to-day variations in temperature. We show that because RONO2 chemistry is the major pathway for NOx loss at this location, ozone production and NOx loss are fundamentally linked. Using in-situ observations, we calculate that daily ozone production increases by 2.3 ppb/°C and daily integrated NOx loss increases by 0.05 ppb/°C. Nearly half of the increase in ozone production is attributable to temperature-driven increases in NOx emissions, most likely from soil microbes. The increase of NOx emissions with temperature suggests that ozone will continue to increase with temperature even if direct anthropogenic NOx emissions decrease dramatically. The links between temperature, soil NOx, and ozone form a positive climate feedback.

46

Secondary Organic Aerosol Formation From In-Situ Oxidation of Near-highway Air

Provat K. Saha

Carnegie Mellon University Motor vehicles are a major source of primary organic aerosol (POA) and precursors for secondary organic aerosol (SOA). However, the extent to which motor vehicles contribute to ambient SOA remains highly uncertain. This study presents in-situ measurements of SOA formation at a near-highway site located within 10 m from Interstate 40, North Carolina. In July-2015 (summer) and February-2016 (winter), ambient air at this site was exposed to different level of oxidant (O3 and OH) concentrations using an Oxidation Flow Reactor (OFR) resulting in hours to weeks of equivalent atmospheric aging. A substantial seasonal difference in SOA formation upon OFR-aging of near-highway air was observed. While a peak enhancement of OA mass concentration of ~ 3-8 µg m-3, with a strong diurnal trend, was observed in summer with 2-4 days of equivalent atmospheric aging, significantly lower enhancement (~0.5-1 µg m-3) was observed during winter. In contrast, measurements in both seasons show nearly consistent changes of bulk OA properties, such as chemical composition and volatility, with OFR-aging. A slightly higher traffic volume (~20%) and a higher prevalence of traffic-related SOA precursors gases (e.g., a higher fraction of semi-volatile emissions in the gas-phase, more evaporative emissions, etc.) during summer compared to winter likely explains part of the observed seasonal difference in SOA formation. Furthermore, biogenic emissions, with very strong temperature-dependence, likely make a significant contribution to the observed roadside OFR-SOA formation in summer. A preliminary analysis indicates that approximate closure can be achieved between the amounts of SOA observed in the OFR and the predicted SOA to form from traffic and biogenic precursors using literature yields. The results from this study also highlight the utility of the OFR for studying the prevalence of SOA precursors in complex real-world settings.

47

Modeling Regional & Global Atmospheric Chemistry Mechanisms - Observing Adverse Respiratory Health Effects due to Tropospheric Ozone Air Pollution

from Modeling Output

Emily Saunders Howard University

Air quality has a strong adverse effect on human health. Ozone is a powerful air pollutant that can irritate the airways causing wheezing and shortness of breath. Meteorological air quality models are used to simulate air pollutants over scales that range from urban to global. The long-range transport of pollutants due to strong winds can have a major impact on local air quality.

Chemical boundary conditions (BCs) are required for regional air quality models. The application of global models to produce BCs for regional air quality models can reflect time-sensitive event information (i.e. biomass burning). Modeling uncertainties can be reduced if the global and regional air quality models use the same or a highly compatible set of chemical mechanisms.

This presentation will discuss the development of the Global Atmospheric Chemistry Mechanism (GACM) and how it will improve air quality modeling. GACM will help supply improved global initial and BCs to regional air quality models that use of RACM2 due to the highly compatible representations of atmospheric chemistry in both mechanisms. GACM is the global version of RACM2 and it was created based upon the chemical reactions in RACM2. To consider the marine environments that would be simulated with GACM marine chemistry reactions were included. To maintain a compact size and computational efficiency for GACM some VOC chemistry was simplified to create space for the additional marine chemistry. GACM will be applicable to current global models and to be used in conjunction with RACM2 based modeling systems to more accurately predict the amount of ozone formed in highly polluted local communities in the US (i.e. California’s South Coast Air Basin/SoCAB).

A zero-dimensional S-Box Model was used to compare the VOC chemistry of RACM2 and GACM and the results showed a less than 1% difference between the output concentrations of O3, NOx, and HO. WRF-Chem was used to understand how RACM2 and GACM would simulate regional tropospheric ozone under real world conditions. WRF-Chem observations show the model under-predicted the simulated O3 by at least 5-10ppb over the 4 km x 4 km gridded SoCAB domain. The comparison between the model results for O3 and the SoCAB site data for O3 displayed about a 30% difference between both mechanisms.

EPA’s Ben-MAP-CE program was used to calculate the respiratory-related health impacts and resulting cost due to the change in O3 concentrations, which can contribute to poor air quality in the SoCAB. The BenMAP results revealed that there are millions of individuals affected by ozone air pollution. The compatible VOC model results showed how both mechanisms would work in a global-regional modeling system, when using GACM to provided BCs. The analysis helped to demonstrate the major influence tropospheric ozone produced in the SoCAB can have on the assessment of negative respiratory health impacts and resulting cost.

Future work will focus on implementing GACM into a global model (i.e. MOZART) to test how well the improved GACM boundary conditions works in regional air quality models.

48

New Particle Formation Leads to Cloud Dimming

Ryan Sullivan Cornell University

New particle formation (NPF), nucleation of condensable vapors to the solid or liquid phase, is a significant source of atmospheric aerosol particle number concentrations. With sufficient growth, these nucleated particles may be a significant source of cloud condensation nuclei (CCN), thus altering cloud albedo, structure, and lifetimes, and insolation reaching the Earth’s surface. I present one of the first numerical experiments to quantify the impact of NPF on cloud radiative properties that is conducted at a convection permitting resolution and that explicitly simulates cloud droplet number concentrations. Consistent with observations, these simulations suggest that in spring over the Midwestern U.S.A., NPF occurs frequently and on regional scales. However, the simulations suggest that NPF is not associated with enhancement of regional cloud albedo as would be expected from an increase of CCN. These simulations indicate that NPF reduces ambient sulfuric acid concentrations sufficiently to inhibit growth of preexisting particles to CCN sizes. This reduction in CCN-sized particles reduces cloud albedo, resulting in a domain average positive top of atmosphere cloud radiative forcing of 10 W m-2 and up to ~ 50 W m-2 in individual grid cells relative to a simulation in which NPF is excluded.

49

Constraining Atmospheric Ammonia Emissions through Novel Observations

Kang Sun Harvard-Smithsonian Center for Astrophysics

As the third most abundant nitrogen species in the atmosphere, ammonia (NH3) is a key component of the global nitrogen cycle. Since the industrial revolution, humans have more than doubled the emissions of NH3 to the atmosphere by industrial nitrogen fixation, revolutionizing agricultural practices, and burning fossil fuels. NH3 is a major precursor to fine particulate matter (PM2.5), which has adverse impacts on air quality and human health. The direct and indirect aerosol radiative forcings currently constitute the largest uncertainties for future climate change predictions. Gas and particle phase NH3 eventually deposits back to the Earth's surface as reactive nitrogen, leading to the exceedance of ecosystem critical loads and perturbation of ecosystem productivity. However, large uncertainties still remain in estimating the magnitude and spatiotemporal patterns of NH3 emissions from all sources and over a range of scales. These uncertainties in emissions also propagate to the model simulations of aerosol formation and nitrogen deposition. To improve our understanding of NH3 emissions, observational constraints are needed from local to global scales. An open-path, quantum cascade laser-based NH3 sensor was developed to address the challenge of sampling sticky NH3 molecules at high frequency and high sensitivity. The sensor has a detection limit (1σ) of 0.15 ppbv NH3 at 20 Hz, a mass of ∼5 kg and consumes ∼50W of electrical power. It was deployed on a 5-m tall flux tower beside a 22,000-animal cattle feedlot to quantify the emission flux of NH3 from agricultural sources together with a suite of other important tracers. Compared to start-of-the-art closed-path NH3 sensors, the open-path NH3 sensor reduced the high-frequency flux loss by one order of magnitude. The NH3 sensor was also integrated into a mobile laboratory and participated in extensive field campaigns, including the NASA DISCOVER-AQ campaigns and the CAREBeijing-NCP campaign in China (400 h on-road time, 18,000 km total sampling distance) to quantify on-road vehicle NH3 emissions. Vehicle NH3:CO2 emission ratios in the U.S. are found to be similar between cities (0.33–0.40 ppbv/ppmv, 15% uncertainty) despite differences in fleet composition, climate, and fuel composition. While Beijing, China has a comparable emission ratio (0.36 ppbv/ppmv) to the U.S. cities, less developed Chinese cities show higher emission ratios (0.44 and 0.55 ppbv/ppmv). If the vehicle CO2 inventories are accurate, NH3 emissions from U.S. vehicles (0.26 ± 0.07 Tg/yr) are more than twice those of the National Emission Inventory (0.12 Tg/yr). Vehicle NH3 emissions are greater than agricultural emissions in counties containing near half of the U.S. population and require reconsideration in urban air quality models. Future opportunities of characterizing NH3 emissions at the global scale enabled by satellite observations will also be discussed.

50

Ambiguity in the Causes for Decadal Trends in Atmospheric Methane and Hydroxyl

Alexander J. Turner

University of California at Berkeley Methane is the second strongest anthropogenic greenhouse gas and its atmospheric burden has more than doubled since 1850. Methane concentrations stabilized in the early 2000s and began increasing again in 2007. Neither the stabilization nor the recent growth are well understood, as evidenced by multiple competing hypotheses in recent literature. Here we use a multi-species 2-box model inversion to jointly constrain 36 years of methane sources and sinks using ground based measurements of methane, methyl chloroform, and the C13/C12 ratio in atmospheric methane (δ13CH4) from 1983 through 2015. We find that the problem, as currently formulated, is under-determined and solutions obtained in previous work are strongly dependent on prior assumptions. Based on our analysis, the mathematically most likely explanation for the renewed growth in atmospheric methane, counter-intuitively, involves a 25 Tg/yr decrease in methane emissions from 2003 to 2016 that is offset by a 7% decrease in global mean hydroxyl (OH) concentrations, the primary sink for atmospheric methane, over the same period. However, we are still able to fit the observations if we assume that OH concentrations are time-invariant (as much of the previous work has assumed) and we then find solutions that are largely consistent with other proposed hypotheses for the renewed growth of atmospheric methane since 2007. We conclude that the current surface observing system does not allow unambiguous attribution of the decadal trends in methane without robust constraints on OH variability, which currently rely purely on methyl chloroform data and its uncertain emissions estimates.

51

Constraining Ammonia Emission Sources in Urban Areas Utilizing Nitrogen Stable Isotopes

Wendell Walters Brown University

Ammonia (NH3) is the primary alkaline molecule in the atmosphere and plays a key role in numerous atmospheric processes that have important implications for human health and climate control via aerosol nucleation. While agricultural activities dominate the overall NH3 emission budget, other emission sources such as fossil-fuel combustion, sewage waste water, waste containers, and animal excreta may play a major role in the urban NH3 emission budget. Urban NH3 concentration measurements tend to be 10-40% greater than predicted by air quality models, highlighting large uncertainties in the urban NH3 emission budget. The analysis of the nitrogen stable isotope composition of NH3 (δ15N-NH3) might be a useful tool for partitioning NH3 emission sources, as different emission sources tend to emit NH3 with distinctive δ15N signatures or “fingerprints”, which could help constrain the urban NH3 budget. However, there is a current lack of δ15N-NH3 measurements of potentially important urban NH3 emission sources, and many of the reported NH3 collection methods have not been verified for its ability to accurately characterize δ15N-NH3.

I present laboratory tested methods to accurately measure δ15N-NH3 from emission sources and from ambient air using gas-scrubbing impingers containing a 0.5% sulfuric acid solution and using honeycomb denuders housed in the ChemComb Speciation Cartridge® coated with a 2% citric acid solution. Based on laboratory tests, the NH3 collection devices have been optimized with respect to flow rate, collection time, and preparation for δ15N-NH3 analysis under a variety of conditions including NH3 concentration and humidity. I find nearly 100% NH3 binding efficiency for the gas-scrubbing impinger at a flow rate of 1 standard liter per minute (SLPM) at elevated NH3 concentrations (1-5 ppmv), and for the honeycomb denuder at a flow rate of 10 SLPM at lower NH3 concentrations (< 200 ppbv). δ15N-NH3 precision is found to be 1.2‰ and 0.8‰ for the gas-scrubbing impinger and the honeycomb denuder, respectively.

Overall, the gas-scrubbing impinger is found suitable for the characterization of δ15N-NH3 signatures from stationary emission sources with relatively high NH3 concentrations (low ppmv). While the ability to sample at a higher flow rate but requiring a lower NH3 concentration (magnitude of ppbv), deems the honeycomb denuders suitable for collecting NH3 in ambient air for isotopic analysis. This provides a method for δ15N-NH3 characterization with a time resolution less than one hour. Preliminary δ15N-NH3 measurements from both vehicles and ambient air are presented, highlighting the potential for δ15N-NH3 to help constrain urban NH3 budgets.

52

The Effect of Different Atmospherically Relevant Salts on Aqueous Phase Partitioning of Organic Compounds

Chen Wang

University of Toronto Partitioning of organic compounds between the gas and aqueous phase can be influenced by the presence of inorganic salts in the aqueous phase, which is known as the salt effect (salting in or out). This salt effect has important implications regarding the reactivity, transport and fate of organic compounds in atmospheric waters, particularly in aerosol particles, which usually contain large amount of ions (ionic strength can be higher than 10 M for deliquescent aerosol particles), including Na+, NH4

+, SO42-, NO3

-, and Cl-. These ions originate from both natural (e.g. sodium chloride from sea spray) and anthropogenic sources (e.g. nitrate and sulfate from NOx and SO2). Empirical data on the salt effect are very sparse for salts other than NaCl. Since it is very difficult to quantify the contribution of individual ions, salt effects are typically only measured for combined salts.

In this study, the salt effects of (NH4)2SO4, Na2SO4, NH4Cl and NH4NO3 for a large number of organic compounds with various functional groups were measured and compared with existing data for NaCl. This addresses the shortage of such data and allows for the analysis of the characteristics of the salt effect for different organic compounds and salts. The results revealed the importance of both salt species and organic compound identities on the salt effect, with the former as the dominant determinant. In general the salt effect showed a decreasing trend of Na2SO4 > (NH)2SO4 > NaCl > NH4Cl > NH4NO3 for the studied organic compounds, implying the following relative strength of the salt effect of individual anions: SO4

2- > Cl- > NO3- and cations: Na+ > NH4

+. The salt effect of different salts is moderately correlated. This indicates very distinct salt effects of different salts on a given organic compound and the same order of salt effect for various organic compounds despite their different size, functional groups, and polarity. For a given salt species, the salt effect for different organic compounds increases with the molecular size and decreases with the polarity of the compound. With the experimental data, models for predicting the salt effect, e.g., poly parameter linear free energy relationships (ppLFERs), were developed and evaluated for individual salt solutions. Comparison with experimental data indicates a generally good performance of the ppLFERs.

The effect of salt mixtures was also investigated, because environmental salt solutions, including aerosol, typically contain mixture of salts. The experimental data indicate that the salt effect of mixtures may not be entirely additive. However, the deviation from additivity, if it exists, is small. Data of very high quality are required to establish whether the effect of constituent ions or salts is additive or not.

53

Evidence for Marine Biogenic Influence on the Composition and Growth of Summertime Arctic Aerosol

Megan D. Willis

University of Toronto

The summertime Arctic lower troposphere is a relatively pristine background aerosol environment dominated by nucleation and Aitken mode particles. Understanding the mechanisms that control the formation and growth of aerosol is crucial for our ability to predict cloud properties and therefore radiative balance and Arctic climate. We present novel, vertically-resolved observations of submicron aerosol composition made during pristine summertime High Arctic background conditions, with low carbon monoxide and black carbon concentrations (< 90 ppbv and < 10 ng/m3, respectively), on six flights from 4 to 12 July, 2014. The methane sulfonic acid (MSA)-to-sulfate ratio peaked near the surface with a mean (quartile range) of 0.10 (0.03 – 0.15), indicating a contribution from ocean derived biogenic sulfur. Similarly, the organic aerosol (OA)-to-sulfate ratio increased towards the surface with a near surface mean (quartile range) of 2.0 (0.6 – 4.6). Both the MSA-to-sulfate and OA-to-sulfate ratios were significantly correlated with a FLEXPART-WRF-predicted measure of air mass residence time over open water, indicating marine influenced OA. External mixing of sea salt aerosol from a much larger number fraction of organic, sulfate and amine-containing particles, together with spatially and temporally homogeneous low wind speeds in the boundary layer (median 4.0 ms-1), suggests a role for secondary organic aerosol formation. In one notable case while flying in the boundary layer above open water, we observed growth of small particles, < 20 nm in diameter, into sizes above 50 nm. Aerosol growth was correlated with the presence of organic aerosol, trimethylamine, and MSA in particles ~80 nm and larger. MSA-to-sulfate ratios up to 0.15 were observed during aerosol growth, demonstrating marine influence, and particles active as cloud condensation nuclei (CCN) were elevated in concentration above background levels of 100 cm-3 up to 220 cm-3. Over all six flights, CCN concentrations were nearly constant (~120 cm-3) when the OA fraction was < 60% and increased to as high as 350 cm-3 when the organic fraction was larger and residence times over open water were longer. Organic species had low hygroscopicity (κOA < 0.1), so we hypothesize that OA participated in growth of particles to CCN-active sizes (i.e., > ~70 nm) and thus contribute to CCN through reduction of the Kelvin effect. Our observations illustrate the importance of marine influenced OA under Arctic background conditions, which are likely to change as the Arctic transitions to larger areas of open water in summer.

54

Large Contributions from Biogenic Carbon to Organic Aerosol in the Southeastern United States

Lu Xu

California Institute of Technology

Atmospheric organic aerosol (OA) has important impacts on climate and human health, but its sources remain poorly characterized. Biogenic monoterpines (MT, C10H16) and sesquiterpenes (SQT, C15H24) are critical precursors of OA. However, the predicted global SOA production from MT and SQT varies from 14 to 246.0 Tg yr-1. This large variation in model estimates introduces significant uncertainties in estimating OA climate forcing and human exposure. Essentially, these model estimates should be evaluated with ambient observations. In this study, we integrate novel lab-in-the-field experiments, extensive ambient ground measurements, and atmospheric transport model to constrain the OA budget from MT and SQT in the southeastern U.S.

Based on widely used positive matrix factorization (PMF) analysis on aerosol mass spectrometer (AMS) measurements and novel lab-in-the-field experiments, we provide direct evidence that newly formed SOA from monoterpenes and sesquiterpenes dominantly contributes to one OA subtype, named as less-oxidized oxygenated organic aerosol (LO-OOA). We use an upgraded regional model (Community Multiscale Air Quality, CMAQ) to simulate SOA production from the oxidation of MT and SQT (denoted as SOAMT+SQT). The modeled SOAMT+SQT accurately reproduces the magnitude and diurnal variability of LO-OOA measured at multiple sites in the southeastern U.S. The agreement between model and measurements supports that LO-OOA can be used as a measure of SOAMT+SQT in the southeastern U.S. We show that the annual production of OA from monoterpenes and sesquiterpenes accounts for 27% of World Health Organization PM2.5 standard, indicating a significant contributor of environmental risk to the 77 million habitants in the southeastern U.S. In addition, the lab-in-the-field approach developed here allows for the study of OA formation under real atmospheric conditions, which bridges laboratory studies and field measurements and provides a direct way to evaluate the atmospheric relevancy of laboratory studies.

55

The Effects of Aerosol Phase State on Secondary Organic Aerosol Formation from the Acid-Catalyzed Reactive Uptake of Isoprene-Derived Epoxydiols

Yue Zhang

University of North Carolina at Chapel Hill

Acid-catalyzed reactions between gas and particle phase constituents are an important formation mechanism for atmospheric secondary organic aerosol (SOA). Aerosol phase state is thought to influence the reactive uptake process of gas phase precursors, especially when the diffusion rate of gas species inside the particles is limited due to high particle viscosity. However, there is little experimental evidence to show and quantify the dependence of reactive uptake processes on particle phase state.

This laboratory study systematically examines the reactive uptake probability of isoprene-derived epoxydiols (IEPOX) onto acidic sulfate particles with three types of pre-existing SOA coatings that represent both biogenic and anthropogenic sources: 𝛼-pinene, toluene, and naphthalene SOA. The experiment is conducted by coupling a potential aerosol mass (PAM) reactor, a flow tube reactor, and a chemical ionization mass spectrometer (CIMS) together. The reactive uptake probability is obtained as a function of SOA composition, oxidation state, coating thickness, and relative humidity (RH). Results show that pre-existing SOA coatings are able to significantly reduce IEPOX reactive uptake probability. At 15% RH, only 5 nm toluene/naphthalene SOA coating results in a reduction of uptake probability of more than one order of magnitude. At 30% and 50% humidity, the uptake probability of particles with a 10 nm coating is reduced to approximately half of the value for uncoated particles. A resistor model is used to estimate the diffusion coefficient of IEPOX in the particle phase by varying the coating thickness of SOA layers at different RHs. The diffusion coefficient is estimated to be 10-12 to 10-18 cm2 s-1, which indicates the SOA is semi-solid to solid. The results suggest potential over-estimation of isoprene-derived SOA if organic coating is not considered in models.

This study can be used in order to accurately characterize the formation and evolution of IEPOX-derived SOA. Moreover, the approach used in this study could be more widely applied to other multiphase chemical systems in regional and global scale models to better predict the impact of SOA on climate, human health, and visibility.

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