Considerable Unaccounted Local Sources of NO(x)Emissions in China Revealed from Satellite

High-resolution (e.g., 5 km) emission data of nitrogenoxides (NOx=NO+NO2) provide localized knowledge of pollutionsources for targeted regulations, yet such data are lacking or inaccurate overmost regions at present. Here we improve our PHLET-based inversionmethod to derive NOxemissions in China at a 5-km resolution in summer2019, based on the TROPOMI-POMINO satellite product of nitrogendioxide (NO2) columns. With low computational costs, our inversionexplicitly accounts for the effects of horizontal transport and nonlinearchemistry. Wefind numerous small-to-medium sources related to minorroads and small human settlements at relatively low affluence levels, inaddition to clear emission signals along major transportation lines,consistent with road line density and Tencent location data. Many small-to-medium sources and transportation emissions are unclear or missing inthe spatial distributions of four widely used emission inventories. Our emissions offer a unique reference for targeted emissioncontrol.