Articles | Volume 18, issue 6
Research article
28 Mar 2018
Research article |  | 28 Mar 2018

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

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

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.

Short summary
While oceanic air is generally thought to be clean, the air pollution over waters in proximity to the coasts is not well recognized. This research indicated that ozone was higher over South China Sea (SCS) than that in the adjacent continental area, while continental anticyclone, tropical cyclone and land breeze favored O3 formation over SCS. In addition, weaker NO titration and stronger atmospheric oxidative capacity led to higher O3 production efficiency over SCS.
Final-revised paper