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Use of OMI Data in Monitoring Air Quality Changes Resulting from NOx 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 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 1
Outline • US EPA emission regulatory programs for NOx • Air quality improvements through 2005 • Use of OMI tropospheric NO 2 to examine air quality changes 2005 to 2008 • Comparisons with Continuous Emissions Monitoring data • Implications for ozone • Plan for attributing satellite-derived NO 2 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
S. -W. Kim et al. (2006) Northeast Summer 2004 model analysis OH Valley WRF-Chem with CEMS adjusted emissions SCIAMACHY Trop. NO 2 Column WRF-Chem with NEI-99 emissions Region % Change 1999 -2005 OH Valley – Emiss. -34% Satellite -38% Northeast – Emiss. -5% Satellite -11%
What has happened since 2005? • OMI tropospheric NO 2 data began in late 2004 – higher spatial resolution, complete global coverage. • US EPA mandated power plant NOx emission reductions under the 1998 NOx State Implementation Plan Call have evolved into what is now called the “NOx 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, NOx 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 NOx reductions. • Tier II Tailpipe NOx Emission Standards – 5% reduction in fleet emissions per year over 2002 to 2010. Increasing Vehicle Miles Traveled partially negated the reductions until 2008.
U. S. Monthly Vehicle Miles Traveled Summer 08 ~5% decrease Source: US DOT, Bureau of Transportation Statistics
Aura/OMI Ozone Monitoring Instrument Aura 2 -dimensional CCD Wavelength range: 270 – 500 nm wavelength ~ 580 pixels Sun-synchronous polar orbit; Equator crossing at 1: 30 PM LT ~ 780 pixels viewing angle ± 57 deg flight direction 2600 -km wide swath; horiz. res. 13 x 24 km at nadir » 7 km/sec 13 km Global coverage every day 2600 km O 3, NO 2, SO 2, HCHO, aerosol, Br. O, OCl. O (~2 sec flight)) 13 km x 24 km (binned & co-added)
OMI Trop. NO 2 July 2005 July 2008
July OMI NO 2 Difference
July 2008 vs. July 2005 OMI Trop. NO 2 -- % change Continuous Emission Monitoring System -- Absolute Changes PA: +11% KY: + 7% Based on EPA NOx Budget Trading Program Progress Reports
July 2005 NO 2 Height of marker proportional to NEI-2002 NOx emissions
July 2008 NO 2
OMI NO 2 Regional Trends +9. 2%
Interpretation and Implications We do not know for certain the reason for the 2008 PA NO 2 increase. Some possible explanations: • Under EPA’s NOx Budget Trading Program a region-wide cap on summertime NOx emissions is set. Sources that control NOx 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 NOx. • 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 NOx emissions over PA could increase ozone production over East Coast Metropolitan Areas.
OMI NO 2 Summer Trend -10. 9% -16. 6% -15. 6% -14. 6%
How does the change in the satellite observations correspond to changes in emissions? Example: Compute correlation between CEMS NOx emission changes and OMI tropospheric NO 2 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 NO 2 column density (2) Compare trend in satellite NO 2 data to trend in model column NO 2 (3) Use CMAQ to define regions of influence near clusters of sources for satellite trend analysis
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 1015 molecules cm-2
Lightning NOx 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.
Summary • OMI tropospheric NO 2 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 NO 2 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.
Acknowledgements • Support from NASA’s Applied Sciences Air Quality Program