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 PM 2.5 precursors are expected. In this paper, we investigate the effects of BEs on O 3 and fine PM (PM 2.5 ) concentrations during a strong photochemical air pollution season in the SMA in Korea. O 3 and PM 2.5 levels are modeled with and without BEs in June 2008. Further, we perform the health impact assessments (HIA) of O 3 and PM 2.5 concentration changes due to BEs to seek useful implications for air quality management by utilizing the adjusted exposure concentration fields for O 3 and PM 2.5 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 ~ 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 PM 2.5 exposure metrics and the subsequent HIA reveal that large mean increments of O 3 , about 8.43 ppb, due to BEs are responsible for approximately 62 all-cause premature mortalities in the SMA in June. However, mean increment of PM 2.5 due to BEs is approximately 0.3 μg m −3 and results in negligible impacts on the all-cause mortality. Significant correlations of O 3 and mortality rates (MR) with the VOC/NO x 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/NO x ] ensure that a 10% decrease in the VOC/NO x 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.