Effect of changing NO x lifetime on the seasonality and long-term trends of satellite-observed tropospheric NO 2 columns over China

Shah, Viral; Jacob, Daniel J.; Li, Ke; Silvern, Rachel F.; Zhai, Shixian; Liu, Mengyao; Lin, Jintai; Zhang, Qiang

Satellite observations of tropospheric inline-formulaNO2 columns are extensively used to infer trends in anthropogenic emissions of nitrogen oxides (inline-formula M5inlinescrollmathml chem normal NO x normal NO + normal NO normal 2 85pt13ptsvg-formulamathimg43e113c44345338daf739742feec27cd acp-20-1483-2020-ie00001.svg85pt13ptacp-20-1483-2020-ie00001.png ), but this may be complicated by trends in inline-formulaNOx lifetime. Here we use 2004–2018 observations from the Ozone Monitoring Instrument (OMI) satellite-based instrument (QA4ECV and POMINO v2 retrievals) to examine the seasonality and trends of tropospheric inline-formulaNO2 columns over central–eastern China, and we interpret the results with the GEOS-Chem chemical transport model. The observations show a factor of 3 increase in inline-formulaNO2 columns from summer to winter, which we explain in GEOS-Chem as reflecting a longer inline-formulaNOx lifetime in winter than in summer (21 h versus 5.9 h in 2017). The 2005–2018 summer trends of OMI inline-formulaNO2 closely follow the trends in the Multi-resolution Emission Inventory for China (MEIC), with a rise over the 2005–2011 period and a 25 % decrease since. We find in GEOS-Chem no significant trend of the inline-formulaNOx lifetime in summer, supporting the emission trend reported by the MEIC. The winter trend of OMI inline-formulaNO2 is steeper than in summer over the entire period, which we attribute to a decrease in inline-formulaNOx lifetime at lower inline-formulaNOx emissions. Half of the inline-formulaNOx sink in winter is from inline-formulaN2O5 hydrolysis, which counterintuitively becomes more efficient as inline-formulaNOx emissions decrease due to less titration of ozone at night. The formation of organic nitrates also becomes an increasing sink of inline-formulaNOx as inline-formulaNOx emissions decrease but emissions of volatile organic compounds (VOCs) do not.

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Shah, Viral / Jacob, Daniel J. / Li, Ke / et al: Effect of changing NOx lifetime on the seasonality and long-term trends of satellite-observed tropospheric NO2 columns over China. 2020. Copernicus Publications.

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