Articles | Volume 15, issue 21
Research article
12 Nov 2015
Research article |  | 12 Nov 2015

Variations of surface ozone at Ieodo Ocean Research Station in the East China Sea and the influence of Asian outflows

J. Han, B. Shin, M. Lee, G. Hwang, J. Kim, J. Shim, G. Lee, and C. Shim

Abstract. Ieodo Ocean Research Station (IORS), a research tower (~ 40 m a.s.l.) for atmospheric and oceanographic observations, is located in the East China Sea (32.07° N, 125.10° E). The IORS is almost equidistant from South Korea, China, and Japan and, therefore, it is an ideal place to observe Asian outflows without local emission effects. The seasonal variation of ozone was distinct, with a minimum in August (37 ppbv) and two peaks in April and October (62 ppbv), and was largely affected by the seasonal wind pattern over east Asia. At IORS, six types of air masses were distinguished with different levels of O3 concentrations by the cluster analysis of backward trajectories. Marine air masses from the Pacific Ocean represent a relatively clean background air with a lowest ozone level of 32 ppbv, which was most frequently observed in summer (July–August). In spring (March–April) and winter (December–February), the influence of Chinese outflows was dominant with higher ozone concentrations of 62 and 49 ppbv, respectively. This study confirms that the influence of Chinese outflows was the main factor determining O3 levels at IORS and its extent was dependent on meteorological state, particularly at a long-term scale.

Short summary
In east Asia, emissions of O3 precursors have gradually increased and O3 concentrations are expected to increase in the near future. Ieodo Ocean Research Station (IORS), located in the East China Sea, is a unique research tower suitable for observing continental outflows from east Asia. In this study, we present long-term measurements of O3 at IORS, describe their characteristic variations, and evaluate their continental influence on the regional background concentrations of O3.
Final-revised paper