1. Use of OMI Data in Monitoring Air Quality Changes Resulting from NO x Emission Regulations over the United States K. Pickering 1, R. Pinder 2, A. Prados 3, D. Allen 4, J. Stehr 4, R. Dickerson 4, S. Ehrman 4, J. Szykman 2, E. Celarier 5, J. Gleason 1 1 NASA Goddard Space Flight Center 2 U. S. Environmental Protection Agency 3 JCET/Univ. of MD Baltimore County 4 University of Maryland, College Park 5 GEST/Univ. of MD Baltimore County

2. Outline US EPA emission regulatory programs for NO x Air quality improvements through 2005 Use of OMI tropospheric NO2 to examine air quality changes 2005 to 2008 Comparisons with Continuous Emissions Monitoring data Implications for ozone Plan for attributing satellite-derived NO2 changes to source emission changes (e.g., clusters of power plants) using US EPA Community Multiscale Air Quality (CMAQ) model Need for addition of lightning and aircraft NO emissions for CMAQ prior to any attribution or inverse modeling studies

3. S.-W. Kim et al. (2006) Summer 2004 model analysis SCIAMACHY Trop. NO2 Column WRF-Chem with NEI-99 emissions WRF-Chem with CEMS adjusted emissions Northeast OH Valley Region% Change 1999-2005 OH Valley – Emiss.-34% Satellite-38% Northeast – Emiss.-5% Satellite-11%

4. What has happened since 2005? OMI tropospheric NO2 data began in late 2004 – higher spatial resolution, complete global coverage. US EPA mandated power plant NO x emission reductions under the 1998 NO x State Implementation Plan Call have evolved into what is now called the “NO x Budget Trading Program”. Results in further summertime power plant emission reductions over the regulated region (19 eastern states) as a whole, but trading program allows flexibility concerning the magnitude of reduction at specific facilities. Over 2500 large combustion units affected. Clean Air Interstate Rule (CAIR) – rule thrown out by courts; recently reinstated. However, NO x emission caps (year-round) have stayed in place (28 states affected). Even more stringent emission rules in some states, as well as court orders, have led to further NO x reductions. Tier II Tailpipe NO x Emission Standards – 5% reduction in fleet emissions per year over 2002 to 2010. Increasing Vehicle Miles Traveled partially negated the reductions until 2008.

5. U. S. Monthly Vehicle Miles Traveled Source: US DOT, Bureau of Transportation Statistics Summer 08 ~5% decrease

6. Aura/OMI Ozone Monitoring Instrument Wavelength range: 270 – 500 nm Sun-synchronous polar orbit; Equator crossing at 1:30 PM LT 2600-km wide swath; horiz. res. 13 x 24 km at nadir Global coverage every day O 3, NO 2, SO 2, HCHO, aerosol, BrO, OClO Aura 13 km (~2 sec flight) ) 2600 km 13 km x 24 km (binned & co-added) flight direction » 7 km/sec viewing angle ± 57 deg 2-dimensional CCD wavelength ~ 580 pixels ~ 780 pixels

7. July 2005 July 2008 OMI Trop. NO2

8. July OMI NO2 Difference

9. Continuous Emission Monitoring System -- Absolute Changes OMI Trop. NO2 -- % change July 2008 vs. July 2005 PA: +11% KY: + 7% Based on EPA NOx Budget Trading Program Progress Reports

10. July 2005 NO2 Height of marker proportional to NEI-2002 NOx emissions

11. July 2008 NO2

12. OMI NO2 Regional Trends +9.2%

13. Interpretation and Implications We do not know for certain the reason for the 2008 PA NO2 increase. Some possible explanations: Under EPA’s NO x Budget Trading Program a region-wide cap on summertime NO x emissions is set. Sources that control NO x to a large degree can sell emission credits to companies that are not implementing controls. Some individual states have stringent emission regulations of their own. Pennsylvania (PA) does not, but some surrounding states do (such as Maryland (MD)). Therefore, PA power companies are free to purchase the emission credits and emit more NO x. PA, MD, and NJ are all linked on the same power grid. Therefore, MD can buy power from PA, which can result in increased PA emissions. One facility in particular is responsible for ~50% of 2008 increase over 2005. Possible Implication: Increased NO x emissions over PA could increase ozone production over East Coast Metropolitan Areas.

14. OMI NO2 Summer Trend -10.9% -14.6% -16.6% -15.6%

15. How does the change in the satellite observations correspond to changes in emissions? Example: Compute correlation between CEMS NOx emission changes and OMI tropospheric NO2 column changes Can the local trends seen in the satellite observations be attributed to emission changes resulting from specific clusters of sources through use of a regional model? (1) Develop method using CMAQ air quality model to relate emissions to NO2 column density (2) Compare trend in satellite NO2 data to trend in model column NO2 (3) Use CMAQ to define regions of influence near clusters of sources for satellite trend analysis

16. Missing NO 2 Aloft When paired with aloft measurements from NASA INTEX, CMAQ underpredicts NO 2 above the mixed layer Consistent on all flights during the summer of 2004 On average 1.07 x 10 15 molecules cm -2

17. Lightning NO x Source Being Added to CMAQ Lightning flash rates predicted for times and locations of convective precipitation in meteorological model. Flash rates scaled on a monthly basis to the NLDN + IC estimate from Boccippio IC/CG climatology Vertical distribution of LNOx production based on observed climatology and direct function of pressure. Production/flash = 500 moles NO Comparison of CMAQ with INTEX-A aircraft data is good up to ~7 km. Aircraft emissions still needed in CMAQ.

18. Summary OMI tropospheric NO2 observations show large decreases (-16% on average; as much as 40%) over the Central US between the Summers of 2005 and 2008. Decreases of 10 – 20% found in Northeast Corridor (Boston to Virginia) over same time period. Summer mean increases of 9% noted over state of Pennsylvania (as much as 60% increase in July 2008 compared with July 2005 in some grid cells). Changes noted in OMI NO2 are generally consistent with Continuous Emissions Monitoring System data and NOx Budget Trading Reports. Reduction in vehicle emissions may have contributed to reductions. Next steps: Examine impact of NOx emission changes on surface ozone in East Coast metro areas along with accompanying meteorology Use CMAQ model in source attribution studies – quantitatively determine if CEMS emission reductions agree with satellite observations Determine air quality changes associated with specific clusters of sources. Lightning and aircraft NO emissions being added to CMAQ.

19. Acknowledgements Support from NASA’s Applied Sciences Air Quality Program