Abstract
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% across the 7 yr. 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 contributed to 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 both more modest and more variable than NO2 reductions from mobile sources (−10 ± 13%).
Highlights
Nitrogen oxides (NO + NO2 ≡ NOx) play an important role in tropospheric chemistry
These results indicate that improved emission control technology for on-road mobile sources has been successful in reducing NO2 concentrations in cities across the United States (US)
In order to explore the impact that the economic recession has had on NO2 concentrations, we examined trends in Ozone Monitoring Instrument (OMI) Berkeley High-Resolution retrieval (BEHR) NO2 prior to, during, and after the economic recession, or 2005–2007, 2007–2009, and 2009–2011, respectively
Summary
Nitrogen oxides (NO + NO2 ≡ NOx) play an important role in tropospheric chemistry. On a regional scale, NOx degrades local air quality due to its dual role in regulating the production of ozone and its contribution to particle formation. Efforts to reduce anthropogenic NOx emissions in North America and Europe have led to dramatic reductions in urban NOx concentrations (Richter et al, 2005; Kim et al, 2006, 2009; Stavrakou et al, 2008; van der A et al, 2008; Konovalov et al, 2010; Russell et al, 2010; Castellanos and Boersma., 2012; Zhou et al, 2012) These reductions are largely attributed to emission control measures; despite the improvements, concentrations in the United States (US) continue to reach levels that promote high ozone and that are detrimental to human health (US Environmental Protection Agency (EPA), 2010). Examples include the Clean Air Interstate Rule (CAIR), which requires reductions in the emissions of NOx produced from power generation in the eastern US, and the Tier II Tailpipe NOx Emissions Standard, which called
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
