Bryan Duncan 1 , Yasuko Yoshida 1 , Jennifer Olson 2 ,

1. The Sensitivity of U.S. Surface Ozone Formation to NOx and VOCs as Viewed from Space: the Ozone Monitoring Instrument (OMI) Bryan Duncan1, Yasuko Yoshida1, Jennifer Olson2, Sandy Sillman3, Christian Retscher1, Ken Pickering1, Randall Martin4, Ed Celarier1, Jim Crawford2 1NASA Goddard Space Flight Center 2NASA Langley Research Center 3University of Michigan 4Dalhousie University October 20, 2009, CMAS meeting, North Carolina

2. SO2 NO2 O3 CO HCHO OMI NO2 OMI HCHO Main Ingredient in Smog NOx + VOCs→Ozone h Which reactant is the limiting reagent that controls ozone production? Ozone has little vertical variation.

3. OMI HCHO/NO2: Air Quality Indicator* *Based on Sillman [1995] Martin et al. [2004] hv NOx + VOCs → Ozone • If HCHO/NO2 is low then one must reduce anthropogenic VOCs to lower ozone. •If HCHO/NO2 is highthen one must reduce NOx to lower ozone. NOTE: HCHO/NO2 gives info on the sensitivity of instantaneous ozone production, not the ozone concentration!

4. OMI HCHO/NO2 : August 2006 Lots of Isoprene = NOx controls Low VOCs = VOC controls VOC controls O3 prod. NOx controls O3 production VOC – limited regime NOx – limited regime Transition is “fuzzy”: ~1.2-2.2!

5. OMI HCHO/NO2 : August 2006 Southwest US Northeast US Toronto Las Vegas Boston Central Valley Phoenix NYC San Francisco Philly DC LA Richmond VOC controls O3 prod. NOx controls O3 production OMI captures gradient from downtown to suburbs to rural areas!

6. Minimum & Maximum Ratios of 9 Summer Months Min Ratio Max Ratio

7. Variability Associated with NOx Emissions The ratio is increasing as NOx emissions decrease. Therefore, ozone formation is becoming more NOx-limited.

8. June-August OMI NO2: 2007-2005 Wildfires in 2007 Point sources 10% lower in 2007 due to NOx Budget Trading Program of EPA. Automobile emissions decreased due to Tier 2 Vehicle and Gasoline Sulfur Program.

9. Variability Associated with Isoprene Isoprene emissions and, subsequently, HCHO increase with temperature. Therefore, HCHO/NO2 should increase with temperature. We know that high O3 events increase with temperature. Therefore, ozone formation should be more NOx-limited during high ozone events. But, NOx emissions decreasing!

11. Conclusions • The OMI ratio appears to be a credible air quality indicator and is consistent with in situ observations. • Ozone production became more NOx-limited over the U.S. from 2005-2007 because of substantial NOx emission reductions. • Ozone production should be more NOx-limited during heat waves in regions with high biogenic emissions. • The fine horizontal resolution allows us to see the gradient in the ratio from urban to suburban to rural areas. • Currently analyzing CMAQ output. Stay tuned!

12. Extra Slides

13. CMAQ Tropospheric Column : HCHO/NO2 4x4 km2 horizontal resolution July 1st – 4th mean in 2007 at 1-2 pm Provided by Yongtao Hu, Georgia Tech

14. Instantaneous Ozone Production Rate (x107 molec/cm3-s) vs HCHO/NO2 (for NO2 columns > 2.5x1015 molec/cm2) Transition: HCHO/NO2 ~1.2-2.2 Assume Transition= 1 CMAQ NASA Langley box model output. (Provided by Jennifer Olson) Transition: HCHO/NO2 1.4-2.6 CMAQ

15. How do tropospheric and PBL columns (x1015 molec/cm2) compare? 1:1 CMAQ 4 km2 horizontal resolution over Southern California. (Provided by Yongtao Hu, Georgia Tech)

16. How does the Instantaneous O3 Production Rate vary with the PBL column (x1015 molec/cm2), [HCHO], and [NO2]? CMAQ 4 km2 horizontal resolution over Southern California. (Provided by Yongtao Hu, Georgia Tech) NASA Langley box model output. (Provided by Jennifer Olson)

17. Above Normal Rainfall Serious Drought Historic Drought OMI HCHO as Proxy for Variability of Isoprene Emissions Major player in AQ! ~22% Variation