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Mobile monitoring and computational fluid dynamics (CFD) modeling are complementary methods to examine spatio-temporal variations of air pollutant concentrations at high resolutions in urban areas. We measured nitrogen oxides (NO x), black carbon (BC), particle-bound polycyclic aromatic hydrocarbons (pPAH), and particle number (PN) concentrations in a central business district using a mobile laboratory. The analysis of correlations between the measured concentrations and traffic volumes demonstrate that high emitting vehicles (HEVs) are deterministically responsible for poor air quality in the street canyon. The determination coefficient (R 2) with the HEV traffic volume is the largest for the pPAH concentration (0.79). The measured NO x and pPAH concentrations at a signalized intersection are higher than those on a road between two intersections by 24% and 25%, respectively. The CFD modeling results reveal that the signalized intersection plays a role in increasing on-road concentrations due to accelerating and idling vehicles (i.e., emission process), but also plays a countervailing role in decreasing on-road concentrations due to lateral ventilation of emitted pollutants (i.e., dispersion process). It is suggested that the number of HEVs and street-canyon ventilation, especially near a signalized intersection, need to be controlled to mitigate poor air quality in a central business district of a megacity.

Impact estimation of biogenic VOCs (Volatile Organic Compounds) to control ambient ozone is needed. For this, BVOCs emission is calculated by using BEIS, and the impact of ozone is estimated with UAM in the research area, Daegu metropolitan city. It is estimated that 59 ppb and 50 ppb of ozone concentration is caused by BVOCs emissions and anthropogenic emissions, respectively. As for tree type, deciduous trees have greater influence than conifers on the daily maximum 1-hr ozone concentration though the former's distribution area is smaller than the latter's. In addition, variation of ozone concentration by BVOCs emission is more sensitive in city areas compared to rural areas. If we change the landscape from woody plants (urban trees) to lower ozone-forming potential (OFP) species, it should lead to a reduction in grids that exceed the national ambient ozone standard.

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