Deep Learning to Evaluate US NO_x Emissions Using Surface Ozone Predictions

Abstract

Abstract Emissions of nitrogen oxides (NO x = NO + NO 2 ) in the United States have declined significantly during the past three decades. However, satellite observations since 2009 indicate total column NO 2 is no longer declining even as bottom‐up inventories suggest continued decline in emissions. Multiple explanations have been proposed for this discrepancy including (a) the increasing relative importance of nonurban NO x to total column NO 2 , (b) differences between background and urban NO x lifetimes, and (c) that the actual NO x emissions are declining more slowly after 2009. Here, we use a deep learning model trained by NO x emissions and surface observations of ozone to assess consistency between the reported NO x trends between 2005 and 2014 and observations of surface ozone. We find that the satellite‐derived trends best reproduce ozone in low NO x emission (background) regions. The 2010–2014 trend from older satellite‐derived emission estimates produced at low spatial resolution results in the largest bias in surface ozone in regions with high NO x emissions, reflecting the blending of urban and background NO x in these low‐resolution top‐down analyses. In contrast, the trend from higher resolution satellite‐based estimates, which are more capable of capturing the urban emission signature, is in better agreement with ozone in high NO x emission regions, and is consistent with the trend based on surface observations of NO 2 . Our results confirm that the satellite‐derived trends reflect anthropogenic and background influences.