Impact of regional trans-boundary ozone associated with complex terrain on urban air quality

In order to clarify the contribution of the trans-boundaries ozone produced in the vicinity of the Daegu metropolitan area in the southeastern part of the Korean Peninsula, several numerical experiments were performed. A fifth-generation Mesoscale Model (MM5) and a Model-3/Community Multiscale Air Quality (CMAQ) model were used to estimate the meteorological wind field and urban air quality, respectively. The topography around the Daegu metropolis is very complicated, with the wind originated within the metropolitan often coupled with that generated over the closely located Busan and Ulsan metropolis. Therefore, the mesoscale wind and ozone distribution patterns in Daegu metropolis are complicated. The contribution of the ozone produced over Busan to the ozone concentration in Daegu increases rapidly at 18 LST, with its maximum contribution reaching 58.1% of the maximum values of the ozone concentration over Daegu. Ozone originating from the Ulsan metropolis is also transported through the east gate of Daegu, with a contribution of 48.1% when measured at Yulha at 18 LST. The trans-boundary ozone from the outside also contributes to the ozone concentration; therefore, the exact concentration of ozone over Daegu cannot be explained from internally produced ozone only. Therefore, trans-boundaries winds and their impact on the ozone concentration should be considered and evaluated to precisely estimate the ozone concentration.