Ozone affected by a succession of four landfall typhoons in the Yangtze River Delta, China: major processes and health impacts

Abstract

Abstract. Landfall typhoon can significantly affect O3 in the Yangtze River Delta (YRD) region. In this study, we investigate a unique case characterized by two multiday regional O3 pollution episodes related to four successive landfall typhoons in the summer of 2018 in the YRD. The results show that O3 pollution episodes mainly occurred during the period from the end of typhoon and the arrival of the next typhoon. The moment that typhoon reached the 24-h warning line and the last moment of typhoon activity in the mainland China can be roughly regarded as time nodes. Meanwhile, the variations of O3 was related to the track, duration and landing intensity of the typhoons. The impact of typhoon on O3 was like a wave superimposed on the background of high O3 concentration in the YRD in summer. When typhoon was near the 24-h warning line before it landed the coast line of the YRD, the prevailing wind originally from the ocean changed to from the inland, and transported lots of precursors from the polluted areas to the YRD. With typhoon, the low temperature, strong upward airflows, more precipitation and wild wind prevented high O3 episodes. After typhoon, the air below the 700 hPa atmospheric layer was warm and dry, which was conductive to the formation of O3 from the abundance of precursors. It is note-worthy that O3 is mainly generated in the middle of boundary layer (~ 1000 m), and then transported to the surface by downward airflows or turbulences. Moreover, O3 can be accumulated and trapped on the ground due to the poor diffusion conditions because the vertical diffusion and horizontal diffusion were suppressed by downward airflows and light wind, respectively. The premature mortalities attributed to O3 exposure in the YRD during the study period is 194.0, more than the casualties caused directly by the typhoons. This work enhances our understanding of how landfall typhoons affect O3 in the YRD, which can be helpful to forecast the O3 pollution synthetically impacted by the subtropical high and typhoon.

Impact of a subtropical high and a typhoon on a severe ozone pollution episode in the Pearl River Delta, China

“…The WRF (v3.9.1)-CMAQ (v4.7.1) model, which has been extensively shown to perform well simulating pollution processes in China (Wang et al, 2015;Zhan et al, 2020;Qu et al, 2021;Zhao et al, 2021), was used to simulate the O3 pollution episode. The WRF model was set with two one-way nested domains with horizontal resolutions of 27 km and 9 km, respectively (Figure 1a).…”

“…However, in recent years the summer and autumn O3 concentration in eastern China, particularly in Beijing-Tianjin-Hebei (Gong and Liao, 2019;Mao et al, 2020), Yangtze River Delta (Shu et al, 2016;Zhan et al, 2020), and Pearl River Delta (PRD) (Deng et al, 2019;He G et al, 2021) actually increasingly exceeded China's national ambient air quality standards (hourly O3 of 200 μg/m 3 , and the maximum daily 8-h average (MDA8) O3 concentrations of 160 μg/m 3 ).…”

“…Furthermore, by comparing the meteorological conditions and the O3 sources in summer and autumn with and without typhoons, Qu et al (2021) revealed that the approach of typhoons accompanied by higher wind speeds and strengthened downdraughts would reduce cloud cover and thus led to higher solar radiation, which was favorable to the O3 production. Zhan et al (2020) analyzed O3 production processes caused by four consecutive typhoons in the summer of 2018 based on model simulations. They found that O3 pollution events in the YRD region mainly occurred between the end of a typhoon and the arrival of the next typhoon.…”