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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 O3 > 84 ppbv, average for northeast U.S. sites Probability of max 8-h O3 > 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 O3 yr-1 (GEOS-CHEM model) Chem prod in troposphere 4900 Chem loss in troposphere 4200 Transport from stratosphere 500 Deposition 1200 ? Simplified Tropospheric Ozone (O3) Chemistry hv O3 hv, H2O OH NO2 NOx NO OH HOx HO2 HNO3 H2O2 CO, VOCs CO, VOCs, NOx VOCs + OH HCHO Role of Formaldehyde (HCHO) HCHO + h 2HO2 + CO HCHO + OH HO2 + CO + H2O 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 2k1[VOC ] OPE k6 [ NO2 ] O3 HOx family = OH + HO2 + RO + RO2 RO2 VOC NO 2 1 O3 PHOx 3 OH NO 6 HNO3 2k1PHO x [VOC ] k6 [ NO2 ][M ] “NOx- saturated” or “VOC-limited” regime O2 4 NO2 P(O3 ) HCHO RO HO2 5 O3 H2O2 PHOx P (O3 ) 2k 4 k5 0.5 [ NO ] “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. H2O2/HNO3 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 NO2 and HCHO columns . . . Diagnose 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 Bey et al., JGR, 1999 Cross-tropopause transport Deposition Martin et al., JGR, 2002a 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/NO2 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 NO2 and HCHO Columns Largely Confined Near the Surface Also Closely Related to NOx and VOC Emissions Tropospheric NO2 column ~ ENOx Tropospheric HCHO column ~ EVOC Boundary Layer NO/ NO2 NO NO2 W ALTITUDE hours CO hours HO2 HCHO hours OH VOC HNO3 Emission Nitrogen Oxides (NOx) 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 NO2 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 320x40 km2, three cross-track scenes • Complete global coverage in 3 days Perform a Spectral Fit of Solar Backscatter Observations absorption Solar Io Backscattered intensity IB Slant optical depth Scattering by Earth surface and by atmosphere “Slant column” l1 l2 wavelength I B (l ) S ln[ ] I o (l ) S eff S EARTH SURFACE Perform a Radiative Transfer Calculation to Account for Viewing Geometry and Scattering Remove Scenes with IB,c > IB,o 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 HCHO Columns Retrieved from GOME (July 1996) 2.5x1016 molecules cm-2 2 1.5 1 0.5 detection limit South Atlantic Anomaly (disregard) 0 -0.5 High HCHO regions reflect VOC emissions from fires, biosphere, human activity Tropospheric NO2 Columns Retrieved from GOME (July 1996) 6x1015 molecules cm-2 4 2 detection limit 0 Martin et al., 2002b GOME Observations Generally Consistent With In Situ Measurements from Aircraft Houston Area Houston Area Latitude (degrees) Tennessee In Situ NO2 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 O3 HOx family = OH + HO2 + RO + RO2 RO2 VOC NO 2 1 O3 PHOx P(O3 ) 3 NO2 NO 6 HNO3 2k1PHO x [VOC ] k6 [ NO2 ][M ] “NOx- saturated” or “VOC-limited” regime O2 4 OH Little sunlight or high NOx HCHO RO HO2 5 O3 H2O2 Lots of sunlight or little NOx PHOx P (O3 ) 2k 4 k5 0.5 [ NO ] “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 SeaWIFS MOPITT MODIS/ SCIAMA MISR CHY MIPAS TES Launch 1979 1999 2002 O3 1995 1999 N CO N CO2 2002 OMI TBD MLS CALIPSO OCO 2004 2004 2004 N/L L N/L N/L L N/L N 2004 N L NO2 N N/L HNO3 N L CH4 N/L L N HCHO N N/L N SO2 N N/L N BrO N N/L N HCN L N N N N 2007 L N/L NO aerosol CloudSat N Increasing spatial resolution N Conclusions Satellite remote-sensing of tropospheric NO2 and HCHO enables global characterization of ozoneNOx-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