Impact of biogenic emissions on early summer ozone and fine particulate matter exposure in the Seoul Metropolitan Area of Korea

Understanding how ozone (O-3) and fine particulate matter (PM) formation respond to the precursor concentrations in the presence of biogenic emissions (BEs) and thereby changes in health effects can be a key step to design effective air quality management plans. This is particularly true in the Seoul Metropolitan Area (SMA), where future significant controls of anthropogenic sources of O-3 and PM2.5 precursors are expected. In this paper, we investigate the effects of BEs on O-3 and fine PM (PM2.5) concentrations during a strong photochemical air pollution season in the SMA in Korea. O-3 and PM2.5 levels are modeled with and without BEs in June 2008. Further, we perform the health impact assessments (HIA) of O-3 and PM2.5 concentration changes due to BEs to seek useful implications for air quality management by utilizing the adjusted exposure concentration fields for O-3 and PM2.5 with an observation fusing (OBF) method. With BEs, daily maximum 8-h average O-3 (maximum 8-h O-3) and secondary organic aerosol (SOA) concentrations in the SMA increase by 17 and 474%, respectively. These increments are associated with significant consumption of photochemical oxidants (O-x), such as a similar to 60% reduction in OH. radicals. The reduction in O-x, conversely, lowers the production of secondary inorganic aerosols (SIOAs) by 2.7%. Adjusted O-3 and PM2.5 exposure metrics and the subsequent HIA reveal that large mean increments of O-3, about 8.43ppb, due to BEs are responsible for approximately 62 all-cause premature mortalities in the SMA in June. However, mean increment of PM2.5 due to BEs is approximately 0.3gm(-3) and results in negligible impacts on the all-cause mortality. Significant correlations of O-3 and mortality rates (MR) with the VOC/NOx ratios across the SMA suggest that controlling volatile organic compounds (VOCs) from anthropogenic sources can be a priority to reduce O-3 levels and population health risks in the SMA. Specifically, linear relationships of log [O-3] and log [MR] to log [VOC/NOx] ensure that a 10% decrease in the VOC/NOx ratios through the VOC abatements would lead to a 1.5% decrease in the O-3 levels and a 4.3% decrease in the MR on average across the SMA.