Abstract
The influences of meteorological conditions and complex topography on ozone (O3) concentrations were evaluated at two different sites [Jung Ang (JA): a semi-closed topography and Seo Chang (SC): a closed topography] within a valley city neighboring coastal metropolitan cities (Busan and Ulsan) during days exhibiting high O3 episodes (8 and 10 August 2006), using the MM5-CMAQ modeling system. The contributions of physical and chemical processes to the O3 concentrations were also assessed within the mixed layers of the two sites (JA and SC) during the study period. High O3 concentrations at site JA on 8 August were the result of combined effects of the horizontal transport (in a north-south direction) of O3 and its precursors and their subsequent reaction with southerly (from Busan) and easterly sea breezes (from Ulsan) and their accumulation due to the convergence of these sea breezes. Such O3 enhancements on 10 August were caused mainly by the vertical transport of O3 and its precursors and partly by their accumulation (from local emission sources) due to weak winds. Unlike site JA, the O3 enhancement at site SC on 8 August was mainly ascribable to horizontal transport (in an east-west direction) from the source regions of Ulsan. On 10 August, vertical transport of downslope flows from the top of mountains largely contributed to O3 concentrations. In addition, the heights of maximum O3 inflow due to horizontal or vertical transport between the two sites during the episodes were different depending on the differences in the heights of mountains and/or the movement directions and intensities of sea breezes.
Highlights
It is well known that the air quality around urban areas can be greatly affected by emission sources, geographical/ topographical features and meteorological conditions within and surrounding these areas
The CMAQ model was run on two nested grid domains because this study focused on the increase or decrease of O3 concentration due to the transport and photochemistry of its precursors emitted from regional- or urbanscale environments
A high O3 concentration at the Jung Ang (JA) site on 8 August was predicted at 1600 LST
Summary
It is well known that the air quality around urban areas can be greatly affected by emission sources, geographical/ topographical features (e.g., coastal and valley areas) and meteorological conditions (e.g., local circulation, transport, and stagnation) within and surrounding these areas. The target area in this study, is located approximately 35 km from the southeastern coast of the Korean Peninsula (Fig. 1) This city includes complex terrain with a valley area surrounded by a number of mountains, public buildings, and residential areas (Song et al 2009; Song et al 2010a). Based on the two dominant wind patterns, the air quality in Yangsan can be affected by the transport of pollutant gases (e.g., NOx and VOCs) due to its location downwind of coastal metropolitan cities, such as Busan (about 15 km south of Yangsan) and Ulsan (30 km northeast of Yangsan), which have large emission sources (e.g., intensive traffic activities, industrial facilities, and shipping). The different wind patterns between the two sites and between the two episodic days will be different
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