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Preprints
https://doi.org/10.5194/acp-2020-342
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-342
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  26 Aug 2020

26 Aug 2020

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This preprint is currently under review for the journal ACP.

Long-term trends in air quality in major cities in the UK and India: A view from space

Karn Vohra1, Eloise A. Marais2,a, Shannen Suckra1,b, Louisa Kramer1,c, William J. Bloss1, Ravi Sahu3, Abhishek Gaur3, Sachchida N. Tripathi3, Martin Van Damme4, Lieven Clarisse4, and Pierre-F. Coheur4 Karn Vohra et al.
  • 1School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK
  • 2School of Physics and Astronomy, University of Leicester, Leicester, UK
  • 3Department of Civil Engineering, Indian Institute of Technology Kanpur, Kanpur, India
  • 4Université libre de Bruxelles (ULB), Spectroscopy, Quantum Chemistry and Atmospheric Remote Sensing (SQUARES), Brussels, Belgium
  • anow at: Department of Geography, University of College London, London, UK
  • bnow at: National Environment & Planning Agency, Kingston, Jamaica
  • cnow at: Ricardo Energy & Environment, Harwell, UK

Abstract. Air quality networks in cities are costly, inconsistent, and only monitor a few pollutants. Space-based instruments provide global coverage spanning more than a decade to determine trends in air quality and address deficiencies in surface networks. Here we target cities in the UK (London and Birmingham) and India (Delhi and Kanpur) and use observations of nitrogen dioxide (NO2) from the Ozone Monitoring Instrument (OMI), ammonia (NH3) from the Infrared Atmospheric Sounding Interferometer (IASI), formaldehyde (HCHO) from OMI as a proxy for non-methane volatile organic compounds (NMVOCs), and aerosol optical depth (AOD) from the Moderate Resolution Imaging Spectroradiometer (MODIS) for PM2.5. We assess the skill of these products at reproducing monthly variability in surface concentrations of air pollutants where available. We find temporal consistency between column and surface NO2 in cities in the UK and India (R = 0.5–0.7) and NH3 at two of three UK supersites (R = 0.5–0.7), but not between AOD and surface PM2.5 (R < 0.4). MODIS AOD is consistent with AERONET at sites in the UK and India (R > = 0.8) and reproduces significant decline in surface PM2.5 in London (2.7 % a−1) and Birmingham (3.7 % a−1) since 2009. We derive long-term trends in the four cities for 2005–2018 from OMI and MODIS and for 2008–2018 from IASI. Concentrations of all pollutants increase in Delhi, suggesting no air quality improvements there, despite rollout of controls on industrial and transport sectors. Kanpur experiences a significant and substantial (3.1 % a−1) increase in PM2.5. Concentrations of NO2, NH3 and PM2.5 decline in London and Birmingham likely due in large part to emissions controls on vehicles. Trends are significant only for NO2 and PM2.5. Reactive NMVOCs decline in Birmingham, but the trend is not significant, and there is a recent (2012–2018) steep (> 9 % a−1) increase in reactive NMVOCs in London. This may reflect increased contribution of oxygenated VOCs from household products, the food and beverage industry, and domestic wood burning, with implications for formation of ozone in a VOC-limited city.

Karn Vohra et al.

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Karn Vohra et al.

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Short summary
We find satellite observations of atmospheric composition generally reproduce variability in surface air pollution, so we use their long record to estimate air quality trends in major UK and Indian cities. Our trend analysis shows that pollutants targeted with air quality policies have not declined in Delhi and Kanpur, but have in London and Birmingham, with the exception of a recent and dramatic increase in reactive volatile organics in London. Unregulated ammonia has increased only in Delhi.
We find satellite observations of atmospheric composition generally reproduce variability in...
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