Sensitivity of Surface Ozone to Nitrogen Oxides and

Sensitivity of Surface Ozone to Nitrogen Oxides and Volatile Organic Compounds Randall Martin Aaron Van Donkelaar Arlene Fiore

Surface Ozone Remains a Major Issue Half of All Canadians and Half of All Americans Live In Regions that Fail to Achieve their Ozone Air Quality Standards (Ozone impairs respiration, reduces crop yields, oxidizes materials) 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 Change Ozone-Temperature Relationship Observed over 1980 -1998 # summer days with 8 -hour O 3 > 84 ppbv, average for northeast U. S. sites Probability of max 8 -h O 3 > 84 ppbv vs. daily max. T 1988, hottest on record! Lin et al. [Atm. Env. 2001]

Tropospheric Ozone • Primary constituent of smog • Major greenhouse gas • Largely controls atmospheric oxidation Global Budget of Tropospheric Ozone Global sources and sinks, Tg O 3 yr-1 (GEOS-CHEM model) Chem prod in troposphere 4900 Chem loss in troposphere 4200 Transport from stratosphere 500 Deposition 1200 ?

Simplified Tropospheric Ozone (O 3) Chemistry hv O 3 hv, H 2 O OH NO 2 NOx NO OH HOx HO 2 HNO 3 H 2 O 2 CO, VOCs, NOx VOCs + OH HCHO Role of Formaldehyde (HCHO) HCHO + h 2 HO 2 + CO HCHO + OH HO 2 + CO + H 2 O

Insignificant Trend (1980 -1995) in Observed Summer Afternoon Ozone Over Most of the United States despite 12% decrease in VOC emissions (no change in NOx emissions) Decreasing trend in major metropolitan centers Fiore et al. , JGR, 1998

Dependence of Ozone Production on NOx and VOCs O 3 HOx family = OH + HO 2 + RO 2 VOC O 3 PHOx OH NO 2 HCHO RO 1 3 4 NO 6 HNO 3 “NOx- saturated” or “VOC-limited” regime RO 2 HO 2 5 O 3 H 2 O 2 “NOx-limited” regime

Ozone Control Strategies Require Independent Information on Effectiveness of Reducing NOx or VOCs Sillman introduced the concept of NOx-VOC indicators, i. e. H 2 O 2/HNO 3 and HCHO/NOy (NOy = total reactive nitrogen) NOx-saturated NOx-limited HCHO strongly correlated with HOx source & VOC oxidation Predicted reduction in peak (afternoon) ozone for a 35% decrease in NOx and VOC emissions VOC Sillman, JGR, 1995 Would like to observe this transition from space Can observe tropospheric NO 2 and HCHO columns. . .

Diagnose Indicators with GEOS-CHEM Model • • Assimilated Meteorology (GEOS) 4 ox 5 o horizontal resolution, 20 layers in vertical O 3 -NOx-VOC chemistry Radiative and chemical effects of aerosols Anthropogenic and natural emissions Bey et al. , JGR, 1999 Cross-tropopause transport Deposition Martin et al. , JGR, 2002 a Calculated Mean Surface Ozone for August 1997

Conduct Three Simulations • Base Case • Reduce Anthropogenic NOx Emissions by 50% • Reduce Anthropogenic VOC Emissions by 50% Fiore et al. , JGR, 2002

Tropospheric HCHO/NO 2 Column Ratio Is an Indicator of the Sensitivity of Afternoon Surface Ozone to NOx and VOC Emissions GEOS-CHEM Model Calculation For Polluted Regions, Mar-Nov NOx Titration NOx Saturated NOx Limited

Tropospheric NO 2 and HCHO Columns Largely Confined Near the Surface Also Closely Related to NOx and VOC Emissions Tropospheric NO 2 column ~ ENOx Tropospheric HCHO column ~ EVOC Boundary Layer NO/ NO 2 NO W ALTITUDE hours Emission Nitrogen Oxides (NOx) CO hours HO 2 HCHO hours OH VOC HNO 3 Emission Volatile Organic Compounds (VOC)

Surface ozone concentrations are sensitive to the ratio of NOx emissions to VOC emissions (ppbv) Sillman and He, 2002

Retrieve Tropospheric NO 2 and HCHO From the GOME Satellite Instrument • Operational since 1995 • Nadir-viewing solar backscatter instrument (237 -794 nm) • Low-elevation polar sunsynchronous orbit, 10: 30 a. m. observation time • Spatial resolution 320 x 40 km 2, three cross-track scenes • Complete global coverage in 3 days

Perform a Spectral Fit of Solar Backscatter Observations absorption Solar Io Backscattered intensity IB l 1 l 2 wavelength Slant optical depth Scattering by Earth surface and by atmosphere “Slant column” EARTH SURFACE

Perform a Radiative Transfer Calculation to Account for Viewing Geometry and Scattering Remove Scenes with IB, c > IB, o IB, c q • LIDORT Radiative Transfer Model [Spurr et al. , 2002] • GOME Clouds Fields [Kurosu et al. , 1999] Ro • GOME Surface Reflectivity [Koelemeijer et al. , 2001] Rc Pc Rs t

HCHO Columns Retrieved from GOME (July 1996) 2. 5 x 1016 molecules cm-2 2 1. 5 1 South Atlantic Anomaly (disregard) 0. 5 detection limit 0 -0. 5 High HCHO regions reflect VOC emissions from fires, biosphere, human activity

Tropospheric NO 2 Columns Retrieved from GOME (July 1996) 6 x 1015 molecules cm-2 4 2 detection limit 0 Martin et al. , 2002 b

GOME Observations Generally Consistent With In Situ Measurements from Aircraft Houston Area Latitude (degrees) Tennessee In Situ NO 2 Measurements by Tom Ryerson In Situ HCHO Measurements by Alan Fried Latitude (degrees)

GOME Observations Show NOx-Limited Conditions Over Most Polluted Regions During August Major Industrial Areas are Clear Exceptions White areas indicate clouds or data below the GOME detection limit August

Dependence of Ozone Production on NOx and VOCs O 3 HOx family = OH + HO 2 + RO 2 VOC O 3 PHOx Little sunlight or high NOx “NOx- saturated” or “VOC-limited” regime OH NO 2 RO 2 NO 2 1 3 4 NO 6 HNO 3 HCHO RO O 2 HO 2 5 O 3 H 2 O 2 Lots of sunlight or little NOx “NOx-limited” regime

Seasonal Evolution from NOx-Limited to NOx-Saturated Conditions in Fall

GOME Observations Provide Confidence in a Recent Model Prediction NOx-Limited in the South and NOx-Saturated in the North in Fall GOME Model Luo et al. , JGR, 2000

Seasonal Maximum in Surface Ozone in Urban China Occurs in Fall (More High-Pressure Systems) In-situ Surface Ozone Measurements Fall NOxsaturated conditions noteworthy Luo et al. , JGR, 2000

Biomass Burning Emissions are Clearly NOx-Limited, In Contrast with NOx-Saturated Conditions Over the Industrial Highveld Also observe plume evolution August

Present and Future Satellite Observations of Tropospheric Composition multiple Platform ERS-2 Terra ENVISAT Aura Sensor TOMS AVHRR/ GOME Sea. WIFS MOPITT MODIS/ SCIAMA MISR CHY MIPAS TES Launch 1979 1999 2002 O 3 1995 1999 N CO 2 2002 OMI TBD MLS CALIPSO OCO 2004 N/L L N/L N 2004 N L NO 2 N N/L HNO 3 N L CH 4 N/L L N HCHO N N/L N SO 2 N N/L N Br. O N N/L N HCN L N N 2007 L N/L NO aerosol Cloud. Sat N Increasing spatial resolution N

Conclusions Satellite remote-sensing of tropospheric NO 2 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