Simulations of wintertime ozone in the Upper Green River Basin, Wyoming, using WRF-Chem

Abstract:

Elevated ozone concentrations have been observed in the western basins of the United States due to increased oil and natural gas production. While several modeling and observational studies have been carried out to study the high wintertime ozone in the Western United States, photochemical models using available emissions data remain unable to model ozone formation. As of the US-EIA 2018 report, Wyoming is the 8th largest producer of natural gas in the US, with 60% of natural gas production in the state being from the Upper Green River Basin (UGRB).

The winter of 2016-2017 (December 2016 - March 2017) recorded several events of ozone concentration exceeding National Ambient Air Quality Standard (NAAQS) of 70 ppb in the UGRB. We used the Weather Research Forecasting (WRF) model with chemistry (WRF-Chem) to simulate a high ozone event observed in the UGRB during a four-day period from 03 to 07 March 2017 and compared the results to seven weather and air quality monitoring stations in the UGRB. The simulations were carried out using the EPA-NEI 2014v2 emission inventory. We compare performance of two chemical mechanisms in WRF-Chem: the Model for Ozone and Related Chemical Tracers (MOZART) and the Regional Atmospheric Chemistry Mechanism (RACM), and compare both mechanisms with observations from the Wyoming Department of Environmental Quality (WYDEQ). MOZART chemistry produces more ozone in the basin compared to RACM, producing ozone concentrations that are similar to observations. However, while the EPA-NEI 2014v2 emission inventory does a reasonable job of simulating NOx concentrations in the basin, it severely underestimates volatile organic compound (VOC) concentrations. The simulations show a good correlation with observed temperature and calm wind conditions that occur during inversion periods that cause ozone episodes.