Spatial and temporal analysis of ambient carbonyls in a densely populated basin area of central Taiwan

The spatial and temporal distributions of ambient carbonyls during the southwest and northeast monsoon seasons in a densely populated basin area were analyzed. The results show that the major carbonyls in ambient were ketones during the both monsoon seasons. The concentrations of carbonyls at daytime and nighttime were in the order: urban > rural > suburban and urban > suburban > rural areas, respectively. The higher carbonyl concentrations occurred in urban area all day, but maximum variation of carbonyl concentrations occurred in rural area. The orders of carbonyl concentrations at daytime and nighttime were irregular during the northeast monsoon season; the variations of carbonyl concentrations in the area were all low. The effects of urban heat island phenomena on the area were negligible, especially during the northeast monsoon season. The ranges of average ratio (northeast to southwest monsoon seasons) of total carbonyl concentrations in urban, suburban, rural areas were 1.0-1.6, 1.5-3.5, and 1.8-2.4, respectively. Because the clear results were obtained during the both monsoons that ambient carbonyls increased with increasing volatile organic compound (VOC) concentrations, the simulation results of VOCs by CMB8.2 model were used to understand the contribution of carbonyls from the primary sources. The order of VOCs and carbonyls source contributions were vehicle exhaust > hi-tech industry > traditional industry > ship and gasoline stations during the both monsoon seasons. Therefore, in order to effectively reduce the carbonyls in ambient air, pollution from vehicle and hi-tech industry must be managed and controlled.