Use of OMI Data in Monitoring Air Quality Changes Resulting from NOx Emission

Regulations over the United States

K. Pickering1, R. Pinder2, A. Prados3, D. Allen4, J. Stehr4, R. Dickerson4, S. Ehrman4, J. Szykman2,

E. Celarier5, J. Gleason1

1 NASA Goddard Space Flight Center2 U. S. Environmental Protection Agency

3 JCET/Univ. of MD Baltimore County4 University of Maryland, College Park5 GEST/Univ. of MD Baltimore County

Outline

• US EPA emission regulatory programs for NOx

• 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

S.-W. Kim et al. (2006)

Summer 2004 model analysis

SCIAMACHYTrop. NO2Column

WRF-Chem withNEI-99 emissions

WRF-Chem withCEMS adjustedemissions

Northeast

OH Valley

Region % Change 1999-2005OH Valley – Emiss. -34%

Satellite -38%Northeast – Emiss.-5%

Satellite -11%

What has happened since 2005?• OMI tropospheric NO2 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

Source: US DOT, Bureau of Transportation Statistics

Summer 08~5% decrease

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

O3, NO2, SO2, 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

July 2005

July 2008

OMI Trop.NO2

July OMI NO2 Difference

Continuous Emission Monitoring System -- Absolute Changes

OMI Trop. NO2 -- % change

July 2008 vs. July 2005

PA: +11%KY: + 7%Based on EPA NOx Budget TradingProgram Progress Reports

July 2005 NO2 Height of marker proportionalto NEI-2002 NOx emissions

July 2008 NO2

OMI NO2RegionalTrends

+9.2%

Interpretation and Implications

We do not know for certain the reason for the 2008 PA NO2 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 NO2 Summer Trend

-10.9%

-14.6%

-16.6%

-15.6%

How does the change in the satellite observations correspond to changes in emissions?

Example: Compute correlation between CEMS NOx emission changes and OMI tropospheric NO2 column changes

Can the local trends seen in the satelliteobservations 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 clustersof sources for satellite trend analysis

Missing NO2 Aloft

• When paired with aloft measurements from NASA INTEX, CMAQ underpredicts NO2 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 predictedfor times and locations ofconvective precipitation inmeteorological model.

Flash rates scaled on a monthlybasis to the NLDN + IC estimate from Boccippio IC/CG climatology

Vertical distribution of LNOx production based on observedclimatology and direct function ofpressure. Production/flash = 500moles NO

Comparison of CMAQ with INTEX-Aaircraft data is good up to ~7 km.Aircraft emissions still needed inCMAQ.

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 metroareas along with accompanying meteorologyUse 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