Simulations of winter ozone in the Upper Green River basin, Wyoming, using WRF-Chem
<p>In the Upper Green River basin (UGRB) of Wyoming and the Uintah Basin of Utah, strong wintertime ozone (O<span class="inline-formula"><sub>3</sub></span>) formation episodes leading to O<span class="inline-formula"><sub>3</sub>&l...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-08-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/23/9413/2023/acp-23-9413-2023.pdf |
| Summary: | <p>In the Upper Green River basin (UGRB) of Wyoming and the Uintah Basin of Utah, strong wintertime ozone (O<span class="inline-formula"><sub>3</sub></span>) formation episodes leading to O<span class="inline-formula"><sub>3</sub></span> mixing ratios occasionally exceeding 70 parts per billion (ppb) have been observed over the last 2 decades. Wintertime O<span class="inline-formula"><sub>3</sub></span> events in the UGRB were first observed in 2005 and since then have continued to be observed intermittently when meteorological conditions are favorable, despite significant efforts to reduce emissions from oil and natural gas extraction and production. While O<span class="inline-formula"><sub>3</sub></span> formation has been successfully simulated using observed volatile organic compound (VOC) and nitrogen oxide (NO<span class="inline-formula"><sub><i>x</i></sub></span>) mixing ratios, successful simulation of these wintertime episodes using emission inventories in a 3-D photochemical model has remained elusive. An accurate 3-D photochemical model driven by an emission inventory is critical to understanding the spatial extent of high-O<span class="inline-formula"><sub>3</sub></span> events and which emission sources have the most impact on O<span class="inline-formula"><sub>3</sub></span> formation. In the winter of 2016/17 (December 2016–March 2017) several high-O<span class="inline-formula"><sub>3</sub></span> events were observed with 1 h mixing ratios exceeding 70 ppb. This study uses the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) to simulate one of the high-O<span class="inline-formula"><sub>3</sub></span> events observed in the UGRB during March 2017. The WRF-Chem simulations were carried out using the 2014 edition of the Environmental Protection Agency National Emissions Inventory (EPA NEI2014v2), which, unlike previous versions, includes estimates of emissions from non-point oil and gas production sources. Simulations were carried out with two different chemical mechanisms: the Model for Ozone and Related Chemical Tracers (MOZART) and the Regional Atmospheric Chemistry Mechanism (RACM), and the results were compared with data from seven weather and air quality monitoring stations in the UGRB operated by the Wyoming Department of Environmental Quality (WYDEQ). The simulated meteorology compared favorably to observations with regard to temperature inversions, surface temperature, and wind speeds. Notably, because of snow cover present in the basin, the photolysis surface albedo had to be modified to predict O<span class="inline-formula"><sub>3</sub></span> in excess of 70 ppb, although the models were relatively insensitive to the exact photolysis albedo if it was over 0.65. O<span class="inline-formula"><sub>3</sub></span> precursors, i.e., NO<span class="inline-formula"><sub><i>x</i></sub></span> and VOCs, are predicted similarly in simulations with both chemical mechanisms, but simulated VOC mixing ratios are a factor of 6 or more lower than the observations, while NO<span class="inline-formula"><sub><i>x</i></sub></span> is also underpredicted but to a lesser degree. Sensitivity simulations revealed that increasing NO<span class="inline-formula"><sub><i>x</i></sub></span> and VOC emissions to match observations produced slightly more O<span class="inline-formula"><sub>3</sub></span> compared to baseline simulations, but an additional sensitivity simulation with doubled NO<span class="inline-formula"><sub><i>x</i></sub></span> emissions resulted in a considerable increase in O<span class="inline-formula"><sub>3</sub></span> formation. These results suggest that O<span class="inline-formula"><sub>3</sub></span> formation in the basin is most sensitive to NO<span class="inline-formula"><sub><i>x</i></sub></span> emissions.</p> |
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| ISSN: | 1680-7316 1680-7324 |