Abstract

Abstract. The Pearl River Delta (PRD) region in South China is faced with severe ambient tropospheric ozone (O3) pollution in autumn and summer, which mostly coincides with the occurrence of typhoons above the Northwest Pacific. With increasingly severe O3 pollution in the PRD under the influence of typhoons, it is necessary to gain a comprehensive understanding of the impact of typhoons on O3 transport, production and accumulation for efficient O3 reduction. In this study, we analysed the general influence of typhoons on O3 pollution in the PRD via systematic comparisons of meteorological conditions, O3 processes and sources on O3 pollution days with and without typhoon occurrence (denoted as the typhoon-induced and no-typhoon scenarios, respectively) and also examined the differences in these influences in autumn and summer. The results show that the approach of typhoons was accompanied by higher wind speeds and strengthened downdraughts in autumn, as well as the inflows of more polluted air masses in summer, suggesting favourable O3 transport conditions in the typhoon-induced scenario in both seasons. However, the effect of typhoons on the production and accumulation of O3 were distinct. Typhoons led to reduced cloud cover, and thus stronger solar radiation in autumn, which accelerated O3 production, but the shorter residence time of local air masses was unfavourable for the accumulation of O3 within the PRD. In contrast, in summer, typhoons increased cloud cover, and weakened solar radiation, thus restraining O3 formation, but the growing residence time of local air masses favoured O3 accumulation. The modelling results using the Community Multiscale Air Quality (CMAQ) model for the typical O3 pollution days suggest increasing contributions from the transport processes and sources outside the PRD for O3 pollution, confirming enhanced O3 transport under typhoon influence in both seasons. The results of the process analysis in CMAQ suggest that the chemical process contributed more in autumn but less in summer in the PRD. Since O3 production and accumulation cannot be enhanced at the same time, the proportion of O3 contributed by emissions within the PRD was likely to decrease in both seasons. The difference in the typhoon influence on O3 processes in autumn and summer can be attributed to the seasonal variation of the East Asian monsoon. From the meteorology–process–source perspective, this study revealed the complex influence of typhoons on O3 pollution in the PRD and their seasonal differences. To alleviate O3 pollution under typhoon influence, emission control is needed on a larger scale, rather than only within the PRD.

Highlights

  • Tropospheric ozone (O3) serves as a secondary pollutant in ambient air and is detrimental for human health and crop production (Wang et al, 2017; Liu et al, 2018; Mills et al, 2018)

  • The significance of typhoons for O3 pollution in the Pearl River Delta (PRD) calls for thorough evaluations of the different causes of O3 pollution with the appearance of typhoons in the Northwest Pacific

  • We revealed the different impacts of typhoons on O3 transport, production and accumulation in the PRD through systematic comparisons of meteorological conditions and the contributions of various O3 processes and sources in the typhoon-induced and no-typhoon scenarios

Read more

Summary

Introduction

Tropospheric ozone (O3) serves as a secondary pollutant in ambient air and is detrimental for human health and crop production (Wang et al, 2017; Liu et al, 2018; Mills et al, 2018). Under unfavourable meteorological conditions, enhanced transport, production and/or accumulation of O3 can all contribute to the O3 pollution within a region (National Research Council, 1991). Based on reports by Huang et al (2005), Lam et al (2005), Jiang et al (2008), Wang et al (2010), Li (2013), Wang et al (2015), Wei et al (2016) and Chen et al (2018), horizontal/vertical transport and chemical production may both be the main contributing process for typhoon-induced O3 pollution in different parts of the PRD. The SA results revealed that emissions within the PRD contributed 40 %–80 % of O3 during typhoon-related O3 episodes (Li et al, 2012; Li, 2013; Chen et al, 2015), suggesting the potentially important role of O3 accumulation for O3 pollution here.

Data sets
Definition and classification of O3 pollution days
Calculation of the trajectories and air parcel residence time
CMAQ modelling: basic setup and modelling methods
Overview: comparison of meteorological parameters in the PRD
O3 production conditions: comparison of clouds
O3 accumulation conditions: comparison of APRTs
Meteorological conditions on the close typhoon-induced days
Comparisons of O3 processes and sources
Findings
Discussion and conclusions
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call