This RAPID project will investigate the atmospheric impacts of the large changes in pollutant emissions due to the massive social and economic slowdown of activity related to the Covid-19 pandemic in the U.S. The research includes the conduct of systematic light aircraft flights to survey urban and industrial emissions sources in the atmospheres of Denver CO and Houston TX to assess the effects of the emissions changes on the production of ozone. Quantifying the impact of such a large emissions change on urban ozone formation rates and yields provides a rigorous and nearly unprecedented check on the models used for U.S. regulatory and research purposes.<br/><br/>The researchers will conduct twenty 5-hour research flights surveying concentrations of ozone (O3), nitrogen oxides (NOx), carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), and water vapor (H2O) in the atmosphere over the cities of Houston TX and Denver CO. The scientists will collaborate with both academic and government modelers to infuse the unique data from this study into a 3-D WRF-Chem research chemical transport model (CTM) to challenge and improve the representation of ozone chemistry, both for this acute situation and under routine emissions scenarios. Historical, highly detailed, research-quality atmospheric data are available for both cities, including data from recent field campaigns in Denver and in Houston. Both cities represent tractable area sources appropriate for study using light aircraft. Houston and the surrounding areas are home to the majority of the U.S. gasoline refining capacity, as well as significant petrochemical industrial capacity. Denver has a substantial number of mobile sources and the region hosts a high level of oil and natural gas activity. This research will provide a benchmark for chemical rates and yields in models. The project takes advantage of this unique opportunity to assess the effects of dramatically changed emissions on ozone production and will gather the data needed to challenge and improve regulatory and research models in the U.S.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.