2023-09-11 ヒューストン大学(UH)
◆彼らの研究結果は、今後のオゾン汚染を緩和する戦略についての示唆を提供しています。彼らの分析によれば、2021年9月に2つのオゾン発生事象があり、その約63％は国の中部および北部から運ばれたオゾンに起因し、約37％は地元の光化学反応に帰因されました。
◆この研究は、ヒューストンの空気汚染が非常に複雑で、高オゾンの原因には地元と地域の両方の理由があることを示しており、地元の排出物の制御が重要であることを強調しています。
＜関連情報＞
- https://uh.edu/news-events/stories/2023/september-2023/09112023-houston-ozone-exceedance.php
- https://www.sciencedirect.com/science/article/abs/pii/S0048969723045060
テキサス州ヒューストンのTRACER-AQキャンペーンにおけるオゾンエピソードの理解： 輸送と前駆物質に対するオゾン生成感受性の役割 Understanding ozone episodes during the TRACER-AQ campaign in Houston, Texas: The role of transport and ozone production sensitivity to precursors
Ehsan Soleimanian, Yuxuan Wang, Wei Li, Xueying Liu, Travis Griggs, James Flynn, Paul J. Walter, Mark J. Estes
Science of the Total Environment Available online: 28 July 2023
DOI:https://doi.org/10.1016/j.scitotenv.2023.165881
Highlights
•Pollutants were transported to Houston from central/northern US in ozone episodes.
•Local circulation patterns interacted with synoptic flows exacerbating ozone events.
•CAMx modeled enhanced ozone production particularly in urban/industrial districts.
•Transported VOC-rich air masses caused NOx-limited conditions over Houston.
•Increased ozone production was found along the transported plume in ozone episodes.
Abstract
This study investigated transport pathways and photochemical formation responsible for ozone exceedances during the September 2021 deployment of the Tracking Aerosol Convection Interactions ExpeRiment/Air Quality (TRACER-AQ) campaign in Houston, Texas. We focused on two ozone episodes, September 6th–September 11th (“Episode 1”) and September 23rd–September 26th (“Episode 2”), when the maximum daily eight-hour average (MDA8) ozone at surface monitors exceeded 70 ppbv. Long-range transport patterns of air masses during these episodes were from the central/northern US. High-resolution (4 km resolution) trajectory analysis with FLEXible PARTicle (FLEXPART) dispersion model revealed local recirculation of air masses and the accumulation of pollutants across Houston contribute to the ozone exceedances. Comprehensive Air Quality Model with extensions (CAMx) driven by 1.33-km resolution meteorology from the Weather Research and Forecast (WRF) tool simulated elevated ozone production rates during ozone episodes across the Houston metropolitan area, with ozone production hotspots mostly over Houston city and industrial districts of the Houston Ship Channel (HSC). The regional increase in ozone production rates was due to the transport of VOC-rich air masses (via northerly flows) that brought ozone precursors to the region, which ultimately caused a transition in the ozone formation tendency from generally VOC-limited to NOx-limited conditions. However, the city of Houston and the HSC remained in a VOC-limited regime because of local NOx emissions that, to some extent, preponderated the impact of transported VOCs. While approximately 37 % of the elevated ozone production was attributed to local photochemistry, the remaining ∼63 % increase in ozone production was due to the transported ozone to the region during episodes, bringing ozone to the Houston region and contributing to ozone exceedances. The outcomes of this study illustrated the synergy between transport and ozone production, both long-range and local scale, which resulted in ozone exceedances in Houston.
