Atmos. Chem. Phys. Discuss., 12, 15419-15452, 2012
www.atmos-chem-phys-discuss.net/12/15419/2012/
doi:10.5194/acpd-12-15419-2012
© Author(s) 2012. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Trends in OMI NO2 observations over the US: effects of emission control technology and the economic recession
A. R. Russell1, L. C. Valin1, and R. C. Cohen1,2
1Department of Chemistry, University of California Berkeley, Berkeley, CA, USA
2Department of Earth and Planetary Sciences, University of California Berkeley, Berkeley, CA, USA

Abstract. Observations of tropospheric NO2 vertical column densities over the United States (US) for 2005–2011 are evaluated using the OMI Berkeley High Resolution (BEHR) retrieval algorithm. We assess changes in NO2 on day-of-week and interannual timescales to assess the impact of changes in emissions from mobile and non-mobile sources on the observed trends. We observe consistent decreases in cities across the US, with an average total reduction of 32 ± 7%. Changes for large power plants have been more variable (−26 ± 12%) due to regionally-specific regulation policies. An increasing trend of 10–20% in background NO2 columns in the Northwestern US is observed. We examine the impact of the economic recession on emissions and find that decreases in NO2 column densities over cities were moderate prior to the recession (−6 ± 5 % yr−1), larger during the recession (−8 ± 5 % yr−1), and then smaller after the recession (−3 ± 4 % yr−1). Differences in the trends observed on weekdays and weekends indicate that prior to the economic recession, NO2 reductions were dominated by technological improvements to the light-duty vehicle fleet but that a decrease in diesel truck activity has dominated emission reductions since the recession. We use the satellite observations to estimate a 34% decrease in NO2 from mobile sources in cities for 2005–2011 and use that value to infer changes in non-mobile sources. We find that reductions in NO2 from non-mobile sources in cities have been more variable than NO2 reductions from mobile sources (−10 ± 13%).

Citation: Russell, A. R., Valin, L. C., and Cohen, R. C.: Trends in OMI NO2 observations over the US: effects of emission control technology and the economic recession, Atmos. Chem. Phys. Discuss., 12, 15419-15452, doi:10.5194/acpd-12-15419-2012, 2012.
 
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