Ozone pollution around a coastal region of South China Sea: interaction between marine and continental air

Hao Wang,Hai Guo,Shichun Zou,Wenzhuo Pan,Xiaobo Huang,Zhenhao Ling,Xinming Wang,Yangzong Zeren,Xiaopu Lyu,Yu Wang,Jin Shen,Fei Jiang

doi:10.5194/acp-18-4277-2018

Abstract

Abstract. Marine atmosphere is usually considered to be a clean environment, but this study indicates that the near-coast waters of the South China Sea (SCS) suffer from even worse air quality than coastal cities. The analyses were based on concurrent field measurements of target air pollutants and meteorological parameters conducted at a suburban site (Tung Chung, TC) and a nearby marine site (Wan Shan, WS) from August to November 2013. The observations showed that the levels of primary air pollutants were significantly lower at WS than those at TC, while the ozone (O3) value was greater at WS. Higher O3 levels at WS were attributed to the weaker NO titration and higher O3 production rate because of stronger oxidative capacity of the atmosphere. However, O3 episodes were concurrently observed at both sites under certain meteorological conditions, such as tropical cyclones, continental anticyclones and sea–land breezes (SLBs). Driven by these synoptic systems and mesoscale recirculations, the interaction between continental and marine air masses profoundly changed the atmospheric composition and subsequently influenced the formation and redistribution of O3 in the coastal areas. When continental air intruded into marine atmosphere, the O3 pollution was magnified over the SCS, and the elevated O3 ( > 100 ppbv) could overspread the sea boundary layer ∼ 8 times the area of Hong Kong. In some cases, the exaggerated O3 pollution over the SCS was recirculated to the coastal inshore by sea breeze, leading to aggravated O3 pollution in coastal cities. The findings are applicable to similar mesoscale environments around the world where the maritime atmosphere is potentially influenced by severe continental air pollution.

Highlights

Ozone (O3) plays a central role in photochemical oxidation processes in the troposphere via direct reaction, photolysis and the subsequent reactions to produce the hydroxyl radical (Monks et al, 2015; Seinfeld and Pandis, 2016)
This study provided an overview of O3 pollution in warm seasons around a coastal region of the South China Sea (SCS), focusing on the influences of interactions between marine and continental atmospheres on air quality in this subtropical region
The concurrent measurements of primary and secondary air pollutants at Tung Chung (TC) and Wan Shan island (WS) from August to November 2013 indicated that O3 was much higher at WS than that at TC, contrary to the more abundant primary air pollutants at TC

Summary

Introduction

Ozone (O3) plays a central role in photochemical oxidation processes in the troposphere via direct reaction, photolysis and the subsequent reactions to produce the hydroxyl radical (Monks et al, 2015; Seinfeld and Pandis, 2016). O3 at surface level is recognized to be a threat to human health (WHO, 2003; Bell et al, 2007) and has a detrimental impact on vegetation (Fowler et al, 2009) and infrastructure (Kumar and Imam, 2013). Tropospheric O3 is the third most important greenhouse gas (IPCC, 2014) and is referred to a short-lived climate pollutant (Shindell et al, 2012). H. Wang et al.: Ozone pollution around a coastal region of South China Sea

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