Non-linear inter-annual variations explain 6.6% of the variance of total NO x emissions. Multivariate trend analysis reveals that soil and lightning NO x combined emissions trends change from −3.95% a −1 during 2005–2009 to 0.60% a −1 from 2009 to 2019, thereby rendering the abrupt slowdown of total NO x emissions reduction. We improve soil NO x emissions estimates using a new observation-based temperature response, which increases the linear correlation coefficient between GEOS-Chem simulated and OMI NO 2 VCDs by 0.05–0.2 over the Central US. To better understand the contributing factors to a flattening of the OMI NO 2 trends, we investigate the role of soil and lightning NO x emissions on this apparent disagreement. EPA reports a steady decline of US anthropogenic NO x emissions in 2005–2019 summers, while NO 2 vertical column densities (VCDs) from the OMI satellite over large spatial domains have flattened since 2009.
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