Impact of a subtropical high and a typhoon on a severe ozone pollution episode in the Pearl River Delta, China
<p>A record-breaking severe ozone (<span class="inline-formula">O<sub>3</sub></span>) pollution episode occurred in the Pearl River Delta (PRD) in early autumn 2019 when the PRD was under the influence of a Pacific subtropical high followed by Typhoon Mitag. I...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-08-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/22/10751/2022/acp-22-10751-2022.pdf |
| Summary: | <p>A record-breaking severe ozone (<span class="inline-formula">O<sub>3</sub></span>) pollution episode occurred in the Pearl River Delta (PRD) in early autumn 2019 when the PRD was under the influence of a Pacific subtropical high followed by Typhoon Mitag. In this study, we analyzed the effects of meteorological and photochemical processes on the <span class="inline-formula">O<sub>3</sub></span> concentration in the PRD during this episode by carrying out the Weather Research Forecast–Community Multiscale Air Quality (WRF-CMAQ) model simulations. Results showed that low relative humidity, high boundary layer height, weak northerly surface wind, and strong downdrafts were the main meteorological factors contributing to <span class="inline-formula">O<sub>3</sub></span> pollution. Moreover, delayed sea breezes that lasted into the night would transport <span class="inline-formula">O<sub>3</sub></span> from the sea back to the land and resulted in secondary <span class="inline-formula">O<sub>3</sub></span> maxima at night. In addition, <span class="inline-formula">O<sub>3</sub></span> and its precursors stored in the residual layer above the surface layer at night can be mixed down to the surface in the next morning, further enhancing the daytime ground-level <span class="inline-formula">O<sub>3</sub></span> concentration on the following day. Photochemical production of <span class="inline-formula">O<sub>3</sub></span>, with a daytime average production rate of about 7.2 <span class="inline-formula">ppb h<sup>−1</sup></span> (parts per billion), is found to be the predominate positive contributor to the <span class="inline-formula">O<sub>3</sub></span> budget of the boundary layer (0–1260 m) during the entire <span class="inline-formula">O<sub>3</sub></span> episode, while the
horizontal and vertical transport fluxes are the dominant negative contributors. This <span class="inline-formula">O<sub>3</sub></span> episode accounted for 10 out of the yearly total of 51 d when the maximum daily 8 h average (MDA8) <span class="inline-formula">O<sub>3</sub></span> concentration exceeded the national standard of 75 ppb in the PRD in 2019. Based on these results, we propose that the enhanced photochemical production of <span class="inline-formula">O<sub>3</sub></span> during the episode is a major cause of the most severe <span class="inline-formula">O<sub>3</sub></span> pollution year since the official <span class="inline-formula">O<sub>3</sub></span> observation started in the PRD in 2006. Moreover, since this <span class="inline-formula">O<sub>3</sub></span> episode is a synoptic-scale phenomenon covering the entire eastern China, we also suggest that the enhanced photochemical production of <span class="inline-formula">O<sub>3</sub></span> in this <span class="inline-formula">O<sub>3</sub></span> episode is a major cause of the extraordinarily high <span class="inline-formula">O<sub>3</sub></span> concentrations observed in eastern China in 2019.</p> |
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| ISSN: | 1680-7316 1680-7324 |