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Observations of tropospheric NO2 vertical column densities over theUnited States (US) for 2005–2011 are evaluated using the OMI Berkeley HighResolution (BEHR) retrieval algorithm. We assess changes in NO2 onday-of-week and interannual timescales to assess the impact of changes inemissions from mobile and non-mobile sources on the observed trends. Weobserve consistent decreases in cities across the US, with an average totalreduction of 32 ± 7% across the 7 yr. Changes for large powerplants have been more variable (−26 ± 12%) due toregionally-specific regulation policies. An increasing trend of 10–20%in background NO2 columns in the northwestern US is observed. Weexamine the impact of the economic recession on emissions and find thatdecreases in NO2 column densities over cities were moderate prior tothe 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 weekdaysand weekends indicate that prior to the economic recession, NO2reductions were dominated by technological improvements to the light-dutyvehicle fleet but that a decrease in diesel truck activity has contributedto emission reductions since the recession. We use the satelliteobservations to estimate a 34% decrease in NO2 from mobile sourcesin cities for 2005–2011 and use that value to infer changes in non-mobilesources. We find that reductions in NO2 from non-mobile sources incities have been both more modest and more variable than NO2 reductionsfrom mobile sources (−10 ± 13%)

atmospheric chemistry and physics

Trends in OMI NO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; observations over the United States: effects of emission control technology and the economic recession