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Shah, Viral

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Shah

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Viral

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Shah, Viral

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2017 - 20192

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Author's Publications: search.filters.isAuthorOfPublication.e6b87b01-c993-4c04-a01e-676ccd72cd05

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    Formaldehyde (HCHO) As a Hazardous Air Pollutant: Mapping Surface Air Concentrations from Satellite and Inferring Cancer Risks in the United States
    (American Chemical Society (ACS), 2017-05-05) Zhu, Lei; Jacob, Daniel; Keutsch, Frank; Mickley, Loretta; Scheffe, Richard; Strum, Madeleine; González Abad, Gonzalo; Chance, Kelly; Yang, Kai; Rappenglück, Bernhard; Millet, Dylan; Baasandorj, Munkhbayar; Jaeglé, Lyatt; Shah, Viral
    Formaldehyde (HCHO) is the most important carcinogen in outdoor air among the 187 hazardous air pollutants (HAPs) identified by the U.S. Environmental Protection Agency (EPA), not including ozone and particulate matter. However, surface observations of HCHO are sparse and the EPA monitoring network could be prone to positive interferences. Here we use 2005–2016 summertime HCHO column data from the OMI satellite instrument, validated with high-quality aircraft data and oversampled on a 5 × 5 km2 grid, to map surface air HCHO concentrations across the contiguous U.S. OMI-derived summertime HCHO values are converted to annual averages using the GEOS-Chem chemical transport model. Results are in good agreement with high-quality summertime observations from urban sites (−2% bias, r = 0.95) but a factor of 1.9 lower than annual means from the EPA network. We thus estimate that up to 6600–12 500 people in the U.S. will develop cancer over their lifetimes by exposure to outdoor HCHO. The main HCHO source in the U.S. is atmospheric oxidation of biogenic isoprene, but the corresponding HCHO yield decreases as the concentration of nitrogen oxides (NOx ≡ NO + NO2) decreases. A GEOS-Chem sensitivity simulation indicates that HCHO levels would decrease by 20–30% in the absence of U.S. anthropogenic NOx emissions. Thus, NOx emission controls to improve ozone air quality have a significant cobenefit in reducing HCHO-related cancer risks.
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    A Two-Pollutant Strategy for Improving Ozone and Particulate Air Quality in China
    (Springer Science and Business Media LLC, 2019-10-14) Li, Ke; Jacob, Daniel; Liao, Hong; Zhu, Jia; Shah, Viral; Shen, Lu; Bates, Kelvin; Zhang, Qiang; Zhai, Shixian
    Fine particulate matter (PM2.5) decreased by 30–40% across China over the 2013–2017 period in response to the governmental Clean Air Action. However, surface ozone pollution worsened over the same period. Model simulations have suggested that the increase of ozone could be driven by the decrease in PM2.5, because PM2.5 scavenges hydroperoxy (HO2) and nitrogen oxide (NOx) radicals that otherwise produce ozone. Here we show observational evidence for this effect with 2013–2018 summer data of hourly ozone and PM2.5 concentrations from 106 sites in the North China Plain. The observations show suppression of ozone pollution at high PM2.5 concentrations, consistent with a model simulation in which PM2.5 scavenging of HO2 and NOx depresses ozone concentrations by 25 ppb relative to PM2.5-free conditions. PM2.5 chemistry makes ozone pollution less sensitive to NOx emission controls, emphasizing the need for controlling emissions of volatile organic compounds (VOCs) which so far have not decreased in China. The new 2018–2020 Clean Air Action calls for a 10% decrease in VOC emissions that should begin to reverse the long-term ozone increase even as PM2.5 continues to decrease. Aggressive reduction of NOx and aromatic VOC emissions should be particularly effective for decreasing both PM2.5 and ozone.