Inferring the anthropogenic NO x emission trend over the United States during 2003-2017 from satellite observations: Was there a flattening of the emission trend after the Great Recession?

Abstract

We illustrate the nonlinear relationships among anthropogenic NOx emissions, NO2 tropospheric vertical column densities (TVCDs), and NO2 surface concentrations using model simulations for July 2011 over the contiguous United States (CONUS). The variations in NO2 surface concentrations and TVCDs are generally consistent and reflect anthropogenic NOx emission variations for high anthropogenic NOx emission regions well. For low anthropogenic NOx emission regions, however, nonlinearity in the anthropogenic-emission-TVCD relationship due to emissions from lightning and soils, chemistry, and physical processes makes it difficult to use satellite observations to infer anthropogenic NOx emission changes. The analysis is extended to 2003-2017. Similar variations in NO2 surface measurements and coincident satellite NO2 TVCDs over urban regions are in sharp contrast to the large variation differences between surface and satellite observations over rural regions. We find a continuous decrease in anthropogenic NOx emissions after 2011 by examining surface and satellite measurements in CONUS urban regions, but the decreasing rate is lower by 9 %-46% than the pre-2011 period.