Improved modelling of soil NO x emissions in a high temperature agricultural region: role of background emissions on NO 2 trend over the US

• Published in: Environmental research letters 2021-08, Vol.16 (8), p.84061
• Main Authors: Wang, Yi, Ge, Cui, Castro Garcia, Lorena, Jenerette, G Darrel, Oikawa, Patty Y, Wang, Jun
• Format: Article
• Language: English
• ISSN: 1748-9326; 1748-9326
• DOI: 10.1088/1748-9326/ac16a3

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. 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. 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. 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. Non-linear inter-annual variations explain 6.6% of the variance of total NO x emissions. As background emissions become relatively larger with uncertain inter-annual variations, the NO 2 VCDs alone at the national scale, especially in the regions with vast rural areas, will be insufficient to discern the trend of anthropogenic emissions.