1.?Introduction . NO x (NO + NO 2 ) emitted mainly from anthropogenic sources, wild fires, lightning, and soil plays a significant role in catalysing tropospheric ozone production and destruction and forming nitrate aerosols (Schindlbacher et al 2004 , Seinfeld and Pandis 2016 ). National Emissions Inventory (NEI) reports a steady decrease of anthropogenic NO x emissions during 2005–2019 summers at a mean rate of ?4.12% a ?1 over the contiguous US. Ozone Monitoring Instrument...