NO_x lifetimes and emissions of cities and power plants in polluted background estimated by satellite observations

Abstract. We present a new method to quantify NO_x emissions and corresponding atmospheric lifetimes from OMI NO₂ observations together with ECMWF wind fields without further model input for sources located in a polluted background. NO₂ patterns under calm wind conditions are used as proxy for the spatial patterns of NO_x emissions, and the effective atmospheric NO_x lifetime is determined from the change of spatial patterns measured at larger wind speeds. Emissions are subsequently derived from the NO₂ mass above the background, integrated around the source of interest.

Lifetimes and emissions are estimated for 17 power plants and 53 cities located in non-mountainous regions across China and the USA. The derived lifetimes for the ozone season (May–September) are 3.8 ± 1.0 h (mean ± standard deviation) with a range of 1.8 to 7.5 h. The derived NO_x emissions show generally good agreement with bottom-up inventories for power plants and cities. Regional inventory shows better agreement with top-down estimates for Chinese cities compared to global inventory, most likely due to different downscaling approaches adopted in the two inventories.