u.s. aerosols: observation from space, effects on climate daniel j. jacob and funding from nasa,...
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U.S. aerosols: U.S. aerosols: observation from space, effects on climate observation from space, effects on climate
Daniel J. Jacob
and funding from NASA, EPRI
with Easan E. Drury, Tzung-May FuLoretta J. Mickley, and Eric M. Leibensperger
ATMOSPHERIC AEROSOLS:ATMOSPHERIC AEROSOLS:ensembles of condensed-phase particles suspended in airensembles of condensed-phase particles suspended in air
Typical aerosol size distribution
number
area
volume
Aerosols are the visible part of the atmosphere:
Pollution off U.S. east coast Dust off West AfricaCalifornia fire plumes
WHY CARE ABOUT ATMOSPHERIC AEROSOLS?WHY CARE ABOUT ATMOSPHERIC AEROSOLS?
Public health
Visibility
Ocean fertilization
Chemistry
Climate forcing
Cloud formation
MAJOR AEROSOL COMPONENTS IN U.S. MAJOR AEROSOL COMPONENTS IN U.S.
Dry mass concentrations
Sulfate: from atmospheric oxidation of SO2 emitted by combustion (mainly coal)Nitrate: from atmospheric oxidation of NOx emitted by combustionAmmonium: from NH3 emitted by agricultureCarbon: elemental carbon from combustion and organic carbon from combustion and vegetationCrustal: suspended mineral dust
Urban air concentrations of particulate matter <2.5 m diameter (PM2.5)
GLOBAL AEROSOL OBSERVATION FROM SPACEGLOBAL AEROSOL OBSERVATION FROM SPACEAerosol optical depths (AODs) at 0.55 m from MODIS and MISR sensors
MODIS
return time 2x/day
MISR
9-day return time
Why are the AODs so different?
van Donkelaar et al. [2006]
Jan 01 – Oct 02
MODIS RETRIEVAL MODIS RETRIEVAL OF AEROSOL OPTICAL DEPTHS (AODs) OVER LANDOF AEROSOL OPTICAL DEPTHS (AODs) OVER LAND
SURFACE
AEROSOL
0.47 m0.65 m2.13 m
• Interpretation of this top-of-atmosphere (TOA) reflectance in terms of AOD requires assumptions on surface reflectance, aerosol optical properties
• Use TOA reflectance at 2.13 m (transparent atmosphere) to derive surface reflectance
• Assume 0.47/2.13 and 0.65/2.13 surface reflectance ratios to obtain atmospheric reflectances at 0.47 and 0.65 m by subtraction
• Assume aerosol optical properties to convert atmospheric reflectance to AOD
• MISR does along-track multi-angle viewing of same aerosol column – better constraints but sparser data
MODIS measures backscatter solar reflectance in several wavelength channels
CONSTRAINING AND TESTING AEROSOL OBSERVATIONS CONSTRAINING AND TESTING AEROSOL OBSERVATIONS FROM SPACE DURING ICARTT CAMPAIGN (Jul-Aug 2004)FROM SPACE DURING ICARTT CAMPAIGN (Jul-Aug 2004)
EASTERN U.S.
IMPROVE surface network: speciated mass concentrations at background sitesAERONET surface network: aerosol optical depths
NASA, NOAA, DOE aircraft: speciated mass concentrations,microphysical & optical properties
MODIS satellite instrument:aerosol optical depths
NASADC-8
IMPROVING THE SURFACE REFLECTANCE CORRECTION IMPROVING THE SURFACE REFLECTANCE CORRECTION FOR MODIS AEROSOL RETRIEVALSFOR MODIS AEROSOL RETRIEVALS
Measuredtop-of-atmosphere (TOA)reflectances(ICARTT period)
2.13 m 0.65 m
Measured 0.65 vs. 2.13TOA reflectances: take lower envelope for given location to derive surface reflectance ratio
Derive aerosol reflectanceat 0.65 m(same procedure for 0.47 m)
Drury et al. [JGR 2008]
Fresno, CAICARTT period
0.65/2.13 surface reflectance ratio
CONVERTING TOA AEROSOL REFLECTANCES TO AODsCONVERTING TOA AEROSOL REFLECTANCES TO AODs
• Use GEOS-Chem model driven by NASA/GEOS assimilated meteorological data with 2ox2.5o resolution
• Model simulates mass concentrations of different aerosol types
• Size distributions and optical properties for different aerosol types are assumed (test with ICARTT data)
• Key advantage of approach is to allow quantitative test of model with the satellite aerosol reflectance data
Standard MODIS algorithm assumes generic aerosol optical properties
Better way is to use local info for given scene from a global 3-D aerosol model
PREVIOUS MODEL EVALUATION: sulfate-nitrate-ammoniumPREVIOUS MODEL EVALUATION: sulfate-nitrate-ammoniumAnnual mean concentrations at IMPROVE sites (2001) – CASTNET for NH4
+
• Sulfate is 100% in aerosol;• Ammonia NH3(g) neutralizes sulfate to form (NH4)2SO4;• Excess NH3(g) if present can combine with HNO3(g) to form NH4NO3 as function of T, RH
Park et al. [AE 2006]
r = 0.96 bias = +10% r = 0.60 bias = +30% r =0.94 bias = +10%
PREVIOUS MODEL EVALUATION: carbonaceous aerosolPREVIOUS MODEL EVALUATION: carbonaceous aerosol
• Primary sources: fossil fuel, biofuel, wildfires• Also large growing-season biogenic source of secondary organic aerosol (SOA)
Elemental carbon (EC) Organic carbon (OC)
volatile organiccompounds (VOCs)
oxidation, multi-stepSOA
Park et al. [AE 2006]
Annual mean concentrations at IMPROVE sites (2001)
r = 0.75 bias = -15% r = 0.70 bias = +20%
PREVIOUS MODEL EVALUATION: mineral dustPREVIOUS MODEL EVALUATION: mineral dust
GEOS-Chem
Local
Asian dust
Saharandust
Fairlie et al. [AE 2007]
Annual mean concentrations at IMPROVE sites (2001)
AEROSOL VERTICAL PROFILES IN ICARTTAEROSOL VERTICAL PROFILES IN ICARTT
NASA DC-8
IMPROVE (<2.5 m)
bulk filter (Dibb, UNH)
PILS (Weber, GIT)
• Sulfate model overestimate: excessive cloud processing?• Unresolved disagreement in ammonium and dust observations
Easan Dury, in prep.
ORGANIC AEROSOL IN ICARTTORGANIC AEROSOL IN ICARTT
PILS water-soluble organic carbon (WSOC) on NOAA P-3 IMPROVE measurements of organic carbon
• Standard reversible SOA (Pankow/Seinfeld):( , )oxidationVOC secondary organic gas (SOG) SOA
K T aerosol • Dicarbonyl SOA (Liggio/Fu):
oxidation cloud uptakemulti-step oxidation, oligomerization
VOC glyoxal, methylglyoxal SOA
Fu et al.(AE, in press)
MEAN AEROSOL VERTICAL PROFILES IN ICARTTMEAN AEROSOL VERTICAL PROFILES IN ICARTT
Obs erved
0 3 6 9 12 15 18
1
2
3
4
5
6
7
8
9
10
11
12
Hei
ght (
km)
Aeros ol Mas s (μg m-3 S T P )
B lack C arbon
Dus t
Ammonium
Nitrate
S ulfate
Organic C arbon
Modeled
0 3 6 9 12 15 18
1
2
3
4
5
6
7
8
9
10
11
12
Hei
ght (
km)
Aeros ol Mas s (μg m-3 S T P )
• Bulk of mass is in boundary layer below 3 km: sulfate, organic (dust?)• Dust, organic dominate above 3 km
Easan Drury, in prep.
AEROSOL OPTICAL PROPERTIES IN ICARTTAEROSOL OPTICAL PROPERTIES IN ICARTT
Single-scattering albedo is fraction ofaerosol extinction due to scattering
AERONET
standard modelAssumption (GADs)
improved fit(this work)
Easan Drury, in prep.
MEAN AEROSOL OPTICAL DEPTHS DURING ICARTTMEAN AEROSOL OPTICAL DEPTHS DURING ICARTT
Model results compared to observations from AERONET network (circles)
Model w/ GADs size distributions Model w/improved size distributions
Easan Drury, in prep.
r = 0.89 bias = -21% r = 0.89 bias = -7%
Main improvement was to reduce the geometric standard deviation in the log-normal size distributions for sulfate and OC from 2.0 to 1.6
IMPROVED MODIS IMPROVED MODIS RETRIEVALRETRIEVAL
OF AEROSOL OPTICAL OF AEROSOL OPTICAL DEPTH DEPTH
This work
standard MODISproduct (c005)
Easan Drury, in prep.
Circles are AERONET data
standard MODISproduct (c004)
c005 is the latest operationalMODIS AOD product (2006)
r=0.84bias =+2%
r=0.84bias =-20%
MAPPING SURFACE PMMAPPING SURFACE PM2.5 2.5 FROM IMPROVED MODIS AODsFROM IMPROVED MODIS AODs
• Shows model organic aerosol underestimate in Southeast (w/out dicarbonyl SOA) • Questions sulfate problem in Northeast
Easan Drury, in prep.
2.52.5
GEOS-Chem surface PMPM = (MODIS AOD)
GEOS-Chem AOD
GLOBAL RADIATIVE FORCING OF CLIMATE BY AEROSOLSGLOBAL RADIATIVE FORCING OF CLIMATE BY AEROSOLS
IPCC [2007]
Large historical offset of greenhouse warming by anthropogenic aerosols
Unlike, CO2, radiative forcing from aerosols is strongly regional and likely to decrease in future: what are the implications for future climate change?
Historical and projected U.S. trendof SO2 emissions
CLIMATE RESPONSE TO SHUTTING DOWN U.S. AEROSOL CLIMATE RESPONSE TO SHUTTING DOWN U.S. AEROSOL
Mickley et al. (in prep.)
THIS REGIONAL CLIMATE RESPONSE FROM U.S. AEROSOL THIS REGIONAL CLIMATE RESPONSE FROM U.S. AEROSOL VANISHES AFTER A FEW DECADESVANISHES AFTER A FEW DECADES
• Explains why previous studies (focusing on 2050 or 2100 endpoints) have found no regional climate response to aerosol emissions• May reflect regional feedbacks important in present atmosphere but already realized in future enhanced-greenhouse atmosphere
Mickley et al. (in prep.)