Space and Ground-Based Decadal Trends of Nitrogen Oxides in Texas

Nitrogen dioxide can have deleterious effects on both human health and on environmental safety. Over the past decade, nitrogen oxides emissions are reported to have decreased by up to 40% over major cities in Texas, primarily due to the advancement of technologies and tightening of emission standards. However, the latest shale oil and natural gas boom in West Texas are reversing the decreasing trends of NO₂ levels. This study presents a quantitative analysis of NO₂ levels over Texas, including the main shale regions and the major cities. We analyzed remotely sensed NO₂ column observations from the Ozone Measuring Instrument (OMI) aboard the NASA Aura Satellite as well as in situ surface NO₂ measurements from the EPA Quality System (AQS) network. Both OMI and AQS datasets display distinct emission reduction rates, while OMI demonstrates unique spatial variation in the trends. Our analysis includes the regions of major oil and natural gas activities where NOx emissions are high and AQS monitors are not abundant. We explore how the changes in NOx impact the trends in O₃ and particulate matter using both observations and model study. This study also found dramatic drop of nitrogen dioxide emissions during stay-at-home orders issued across Texas in the middle of March 2020.