1. The Sensitivity of U.S. Surface Ozone Formation to NO x and VOCs as Viewed from Space: the Ozone Monitoring Instrument (OMI) Bryan Duncan 1, Yasuko Yoshida 1, Jennifer Olson 2, Sandy Sillman 3, Christian Retscher 1, Ken Pickering 1, Randall Martin 4, Ed Celarier 1, Jim Crawford 2 1 NASA Goddard Space Flight Center 2 NASA Langley Research Center 3 University of Michigan 4 Dalhousie University October 20, 2009, CMAS meeting, North Carolina

2. NO x + VOCs → Ozone Main Ingredient in Smog OMI NO 2 OMI HCHO h SO 2 NO 2 HCHO CO O3O3 Ozone has little vertical variation. Which reactant is the limiting reagent that controls ozone production?

3. NO x + VOCs → Ozone OMI HCHO/NO 2 : Air Quality Indicator* If HCHO/NO 2 is low then one must reduce anthropogenic VOCs to lower ozone. If HCHO/NO 2 is high then one must reduce NO x to lower ozone. hvhv NOTE: HCHO/NO 2 gives info on the sensitivity of instantaneous ozone production, not the ozone concentration! *Based on Sillman [1995] Martin et al. [2004]

4. OMI HCHO/NO 2 : August 2006 VOC controls O 3 prod.NO x controls O 3 production Lots of Isoprene = NO x controls Low VOCs = VOC controls Transition is “fuzzy”: ~1.2-2.2! NO x – limited regimeVOC – limited regime

5. VOC controls O 3 prod.NO x controls O 3 production OMI HCHO/NO 2 : August 2006 Southwest USNortheast US LA San Francisco Las Vegas Central Valley Toronto DC Philly NYC Richmond Boston Phoenix OMI captures gradient from downtown to suburbs to rural areas!

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

7. The ratio is increasing as NO x emissions decrease. Therefore, ozone formation is becoming more NO x -limited. Variability Associated with NO x Emissions

8. June-August OMI NO 2 : 2007-2005 Wildfires in 2007 Point sources 10% lower in 2007 due to NO x Budget Trading Program of EPA. Automobile emissions decreased due to Tier 2 Vehicle and Gasoline Sulfur Program.

9. Variability Associated with Isoprene Therefore, ozone formation should be more NO x -limited during high ozone events. But, NO x emissions decreasing! Isoprene emissions and, subsequently, HCHO increase with temperature. Therefore, HCHO/NO 2 should increase with temperature. We know that high O 3 events increase with temperature.

11. Conclusions  The OMI ratio appears to be a credible air quality indicator and is consistent with in situ observations.  Ozone production became more NO x -limited over the U.S. from 2005-2007 because of substantial NO x emission reductions.  Ozone production should be more NO x -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/NO 2 4x4 km 2 horizontal resolution July 1 st – 4 th mean in 2007 at 1-2 pm Provided by Yongtao Hu, Georgia Tech

14. Instantaneous Ozone Production Rate (x10 7 molec/cm 3 -s) vs HCHO/NO 2 Transition: HCHO/NO 2 ~1.2-2.2 Transition: HCHO/NO 2 1.4-2.6 (for NO 2 columns > 2.5x10 15 molec/cm 2 ) Assume Transition= 1 NASA Langley box model output. (Provided by Jennifer Olson) CMAQ

15. CMAQ 4 km 2 horizontal resolution over Southern California. (Provided by Yongtao Hu, Georgia Tech) How do tropospheric and PBL columns (x10 15 molec/cm 2 ) compare? 1:1

16. How does the Instantaneous O 3 Production Rate vary with the PBL column (x10 15 molec/cm 2 ), [HCHO], and [NO 2 ]? CMAQ 4 km 2 horizontal resolution over Southern California. (Provided by Yongtao Hu, Georgia Tech) NASA Langley box model output. (Provided by Jennifer Olson)

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