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

Abstract

Abstract. Landfall typhoons 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 a typhoon to the arrival of the next typhoon. The time when a typhoon reached the 24 h warning line and the time when the typhoon dies away in mainland China can be roughly regarded as time nodes. Meanwhile, the variations of O3 were related to the track, duration and landing intensity of the typhoons. The impact of typhoons on O3 was like a wave superimposed on the background of high O3 concentration in the YRD in summer. When a typhoon was near the 24 h warning line before it landed on the coastline of the YRD, the prevailing wind originally from the ocean changed to be from inland, and it transported lots of precursors from the polluted areas to the YRD. Under influences of the typhoon, the low temperature, strong upward airflows, more precipitation and wild wind hindered occurrences of high O3 episodes. After the passing of the typhoon, the air below the 700 hPa atmospheric layer was warm and dry, and the downward airflows resumed. The low troposphere was filed with high concentration of O3 due to O3-rich air transported from the low stratosphere and strong photochemical reactions. It is noteworthy that O3 was mainly generated in the middle of the boundary layer (∼ 1000 m) instead of at the surface. High O3 levels remained in the residual layer at night, and would be transported to the surface by downward airflows or turbulence by the second day. 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 deaths attributed to O3 exposure in the YRD during the study period were 194.0, more than the casualties caused directly by the typhoons. This work has enhanced our understanding of how landfall typhoons affect O3 in the YRD and thus can be useful in forecasting O3 pollution in regions strongly influenced by typhoon activities.

Surface Ozone in the Yangtze River Delta, China: A Synthesis of Basic Features, Meteorological Driving Factors, and Health Impacts

“…Figure 3 further shows monthly MDA8 O 3 in the 26 cities in the YRD from 2015 to 2019, the monthly MDA8 O 3 in most cities over the YRD reaches its maximum in May or June, and then O 3 concentration slowly decreases due to Asian summer monsoon (He et al., 2008; Hou et al., 2014; Zhou et al., 2013). Around early autumn, MDA8 O 3 in some cities can reach a second peak, which may be related to typhoon activities (Shu et al., 2016; Zhan et al., 2020). In general, high O 3 concentration in the YRD tends to appear in warm seasons (April‐September), which is consistent with the result of TCO (Figure ).…”

“…Zhan et al. (2020) found that synoptic systems, such as typhoons, can largely impact O 3 pollution episodes. However, these studies only focused on individual stations or a couple of representative cases.…”

Positive and negative influences of landfalling typhoons on tropospheric ozone over southern China

“…Previous studies show that surface ozone concentrations in PRD and YRD are enhanced when typhoons are 700-1000 km away and when typhoons cross the 24-h warning line (thick black dashed line in Fig. 1) (e.g., Huang et al, 2006;Zhan et al, 2020). In addition to these valuable findings of ozone enhancement over the developed regions, this paper examines the overall surface ozone behaviours associated with landfalling typhoons over southern China, and comprehensively addresses both positive and negative impacts of typhoons on surface ozone concentrations in the following part.…”

“…It is also documented that surface ozone concentrations increase over southwestern Taiwan 2 to 4 days before the passage of typhoons (Hung and Lo, 2015). Recently, Zhan et al (2020) found that in YRD ozone pollution episodes mainly occurred when a typhoon reaches the 24-h warning line (thick dashed line in Fig. 1) and the previous typhoon dies away in mainland China.…”

“…Previous studies suggested that TCs often modulate meteorological conditions and hence alter photochemical production, accumulation, transport and dispersion of ozone. For example, when TCs approach, the fine and hot weather are associated with strong solar radiation and high temperature, and the overwhelming downward air motions are conducive to low wind speed and stable atmospheric boundary layer (ABL), all of which are responsible for high ozone episodes in the developed and populated Pearl River Delta (PRD) and Yangtze River Delta (YRD) regions (e.g., Shu et al, 2016;Zhan et al, 2020). Still, it is not clear whether these findings of TCs' impacts based on individual cases, are applicable over large domains, e.g., both coastal regions and neighbouring inland provinces in southern China.…”