Sensitivity of Surface Ozone to Nitrogen Oxides andSensitivity of Surface Ozone to Nitrogen Oxides andVolatile Organic CompoundsVolatile Organic Compounds

Arlene FioreRandall Martin

Aaron Van Donkelaar

Surface Ozone Remains a Major Issue Surface Ozone Remains a Major Issue Half of All Canadians and Half of All Americans Live In Regions that Fail Half of All Canadians and Half of All Americans Live In Regions that Fail

to Achieve their Ozone Air Quality Standardsto Achieve their Ozone Air Quality Standards(Ozone impairs respiration, reduces crop yields, oxidizes materials)(Ozone impairs respiration, reduces crop yields, oxidizes materials)

Observed Peak Surface Ozone Concentration For a “Typical” Episode Observed Peak Surface Ozone Concentration For a “Typical” Episode

1-hour Average Peak Concentration

           0-60 ppb

           61-79 ppb

           80-99 ppb

           100-110 ppb

           111-124 ppb

           125+ ppb

Surface Ozone is Highly Sensitive to Climate ChangeSurface Ozone is Highly Sensitive to Climate ChangeOzone-Temperature Relationship Observed over 1980-1998Ozone-Temperature Relationship Observed over 1980-1998

Probability of max 8-h O3 > 84 ppbvvs. daily max. T

# summer days with 8-hour O3 > 84 ppbv,average for northeast U.S. sites

Lin et al. [Atm. Env. 2001]

1988, hottest on record!

?

Tropospheric Ozone

Global sources and sinks, Tg O3 yr-1 (GEOS-CHEM model)

Chem prod in troposphere

4900 Chem loss in troposphere

4200

Transport from stratosphere

500 Deposition 1200

•Primary constituent of smog

•Major greenhouse gas

•Largely controls atmospheric oxidation

Global Budget of Tropospheric Ozone

CO, VOCs, NOx

HO2OH

NONO2

H2O2

O3

hv, H2O

hvHNO3

OH

VOCs + OH HCHO

HCHO + h 2HO2 + CO

HCHO + OH HO2 + CO + H2O

CO, VOCs

Simplified Tropospheric Ozone (O3) Chemistry

Role of Formaldehyde (HCHO)

NOx

HOx

Insignificant Trend (1980-1995) in Observed Summer Insignificant Trend (1980-1995) in Observed Summer Afternoon Ozone Over Most of the United States despite 12% Afternoon Ozone Over Most of the United States despite 12%

decrease in VOC emissions (no change in NOdecrease in VOC emissions (no change in NOxx emissions) emissions)

Decreasing trend in major metropolitan centersDecreasing trend in major metropolitan centers

Fiore et al., JGR, 1998

Dependence of Ozone Production on NODependence of Ozone Production on NOxx and VOCs and VOCs

HOx family = OH + HO2 + RO + RO2

OH

RO2 RO

HO2

HNO3 H2O2O3

O3

O3

PHOx

1

2

34

56

“NOx- saturated” or“VOC-limited” regime

“NOx-limited” regime

VOC

NO

O2

NO

NO2

HCHO

]][[

][2)(

26

13 MNOk

VOCPkOP xHO ][2)(

5.0

543 NOk

PkOP HOx

][

][2

26

1

NOk

VOCkOPE

Ozone Control Strategies Require Independent Ozone Control Strategies Require Independent Information on Effectiveness of Reducing NOInformation on Effectiveness of Reducing NOxx or VOCs or VOCs

Would like to observe this transition from space

Can observe tropospheric NO2 and HCHO columns . . .

Sillman introduced the concept of NOx-VOC indicators, i.e. H2O2/HNO3 and HCHO/NOy (NOy = total reactive nitrogen)

Sillman, JGR, 1995

Predicted reduction in peak (afternoon) ozone for a 35% decrease in NOx and VOC emissions

VOC

HCHO strongly correlated with HOx source & VOC oxidation

NOx-limitedNOx-saturated

Diagnose Indicators with GEOS-CHEM ModelDiagnose Indicators with GEOS-CHEM Model• Assimilated Meteorology (GEOS)

• 4ox5o horizontal resolution, 20 layers in vertical

• O3-NOx-VOC chemistry

• Radiative and chemical effects of aerosols

• Anthropogenic and natural emissions

• Cross-tropopause transport

• Deposition

Bey et al., JGR, 1999

Martin et al., JGR, 2002a

Calculated Mean Surface Ozone for August 1997

Conduct Three SimulationsConduct Three Simulations• Base Case

• Reduce Anthropogenic NOx Emissions by 50%

• Reduce Anthropogenic VOC Emissions by 50%

Fiore et al., JGR, 2002

Tropospheric HCHO/NOTropospheric HCHO/NO22 Column Ratio Is an Indicator of the Sensitivity of Column Ratio Is an Indicator of the Sensitivity of

Afternoon Surface Ozone to NOAfternoon Surface Ozone to NOxx and VOC Emissions and VOC Emissions

GEOS-CHEM Model Calculation For Polluted Regions, Mar-NovGEOS-CHEM Model Calculation For Polluted Regions, Mar-Nov

NOx Limited

NOx SaturatedNOx Titration

Tropospheric NOTropospheric NO22 and HCHO Columns Largely Confined Near the Surface and HCHO Columns Largely Confined Near the Surface

Also Closely Related to NOAlso Closely Related to NOx x and VOC Emissionsand VOC Emissions

Emission

NO NO2

HNO3

hours

Nitrogen Oxides (NOx) Volatile Organic Compounds (VOC)

Emission

VOC

OHHCHO hoursCO

hours

Boundary Layer

NO/NO2

W ALTITUDE

Tropospheric NO2 column ~ ENOx

Tropospheric HCHO column ~ EVOC

HO2

Surface ozone concentrations are sensitive to the Surface ozone concentrations are sensitive to the ratio of NOratio of NOxx emissions to VOC emissions emissions to VOC emissions

Sillman and He, 2002

(ppbv)

Retrieve Tropospheric NORetrieve Tropospheric NO22 and HCHO From the and HCHO From the

GOME Satellite InstrumentGOME Satellite Instrument•Operational since 1995

•Nadir-viewing solar backscatter instrument (237-794 nm)

• Low-elevation polar sun-synchronous orbit, 10:30 a.m. observation time

• Spatial resolution 320x40 km2, three cross-track scenes

• Complete global coverage in 3 days

Perform a Spectral Fit of Solar Backscatter ObservationsPerform a Spectral Fit of Solar Backscatter Observations

absorption

wavelength

Slant optical depth

EARTH SURFACE

Scattering by Earth surface and by atmosphere

Backscatteredintensity IB

“Slant column”

])(

)(ln[

o

BS I

I

SeffS

Solar Io

Perform a Radiative Transfer Calculation to Account for Viewing Perform a Radiative Transfer Calculation to Account for Viewing Geometry and ScatteringGeometry and Scattering

Remove Scenes with IRemove Scenes with IB,c B,c > I> IB,oB,o

RcRo

IB,o IB,c

Pc

Rs

•LIDORT Radiative Transfer Model [Spurr et al., 2002]

•GOME Clouds Fields [Kurosu et al., 1999]

•GOME Surface Reflectivity [Koelemeijer et al., 2001]

HCHO Columns Retrieved from GOME (July 1996) HCHO Columns Retrieved from GOME (July 1996)

High HCHO regions reflect VOC emissions from fires, biosphere, human activity

-0.5

0

0.5

1

1.5

2

2.5x1016

moleculescm-2

SouthAtlanticAnomaly(disregard)

detectionlimit

Martin et al., 2002b

Tropospheric NOTropospheric NO22 Columns Retrieved from GOME Columns Retrieved from GOME

(July 1996) (July 1996)

6x1015

moleculescm-2

2

0

4

detectionlimit

GOME Observations Generally Consistent With GOME Observations Generally Consistent With In Situ Measurements from AircraftIn Situ Measurements from Aircraft

Latitude (degrees)

Houston Area Houston Area

Tennessee

Latitude (degrees)

In Situ NO2 Measurements by Tom Ryerson

In Situ HCHO Measurements by Alan Fried

GOME Observations Show NOGOME Observations Show NOxx-Limited Conditions Over -Limited Conditions Over

Most Polluted Regions During AugustMost Polluted Regions During AugustMajor Industrial Areas are Clear ExceptionsMajor Industrial Areas are Clear Exceptions

August

White areas indicate clouds or data below the GOME detection limit

Dependence of Ozone Production on NODependence of Ozone Production on NOxx and VOCs and VOCs

HOx family = OH + HO2 + RO + RO2

OH

RO2 RO

HO2

HNO3 H2O2O3

O3

O3

PHOx

1

2

34

56

“NOx- saturated” or“VOC-limited” regime

“NOx-limited” regime

VOC

NO

O2

NO

NO2

HCHO

]][[

][2)(

26

13 MNOk

VOCPkOP xHO ][2)(

5.0

543 NOk

PkOP HOx

Little sunlight or high NOx

Lots of sunlight or little NOx

Seasonal Seasonal Evolution from Evolution from NOx-Limited to NOx-Limited to NOx-Saturated NOx-Saturated

Conditions in FallConditions in Fall

GOME Observations Provide Confidence in a Recent Model PredictionGOME Observations Provide Confidence in a Recent Model Prediction NOx-Limited in the South and NOx-Saturated in the North in FallNOx-Limited in the South and NOx-Saturated in the North in Fall

Luo et al., JGR, 2000

GOME Model

Seasonal Maximum in Surface Ozone in Urban China Seasonal Maximum in Surface Ozone in Urban China Occurs in Fall (More High-Pressure Systems)Occurs in Fall (More High-Pressure Systems)

In-situ Surface Ozone Measurements

Luo et al., JGR, 2000

Fall NOx-saturated conditions noteworthy

Biomass Burning Emissions are Clearly NOBiomass Burning Emissions are Clearly NOxx-Limited, In -Limited, In

Contrast with NOContrast with NOxx-Saturated Conditions Over the -Saturated Conditions Over the

Industrial Highveld Industrial Highveld

August

Also observe plume evolution

Platform multiple ERS-2 Terra ENVISAT Aura CloudSat TBD

Sensor TOMS AVHRR/SeaWIFS

GOME MOPITT MODIS/MISR

SCIAMACHY

MIPAS TES OMI MLS CALIPSO OCO

Launch 1979 1995 1999 1999 2002 2002 2004 2004 2004 2004 2007

O3 N N/L L N/L N L

CO N N/L L N/L

CO2 N/L N

NO L

NO2 N N/L N

HNO3 L L

CH4 N/L N

HCHO N N/L N

SO2 N N/L N

BrO N N/L N

HCN L

aerosol N N N N N N

Present and Future Satellite Observations of Present and Future Satellite Observations of Tropospheric CompositionTropospheric Composition

Increasing spatial resolution

ConclusionsConclusions

Satellite remote-sensing of tropospheric NO2 and HCHO enables global characterization of ozone-NOx-VOC sensitivity

Most of the world is NOx-limited, especially during summer

NOx-saturated (VOC-limited) conditions occur under decreased sunlight or in major industrial centers