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The importance of biogenic volatile organic compounds (BVOCs) in understanding of air-quality and climate on regional to global scales has been highlighted in a number of modeling and observational studies. At the same time, another important emerging research topic in atmospheric chemistry is the regional and global impacts of fast growing East Asian megacities. These two research topics must be integrated in order to adequately understand and address air quality challenges emerging from Eastern Asian megacities surrounded by planted or natural forest areas. We present initial measurement results for May, June and September 2011 from the Taehwa Research Forest (TRF) which has been developed to serve as a long term observatory for investigating biosphere-atmosphere interactions at the edge of the Seoul Metropolitan Area (population of ∼23.5 million). The comprehensive measurement datasets of ozone and its precursors such as CO, NOx, SO2 and VOCs shows that high ozone episodes in the suburban site could not be explained by just anthropogenic pollutants alone. In addition, isoprene (C5H8) and monoterpenes (C10H16) were observed as two of the most important OH chemical sinks inside of the forest canopy. In order to understand the impacts of these BVOCs on ozone and related photochemistry, we conducted model sensitivity simulations using a coupled meteorology-chemistry model (WRF-Chem) for conditions including with and without BVOC emissions. The modeling results suggest that BVOC emissions could enhance regional daytime ozone production from 5 to 20 ppbv. The observed temporal variations in ozone correspond well with the variations in BVOCs, which likely reflects the influence of BVOCs on ozone formation. These findings strongly suggest that interactions between anthropogenic pollutants and BVOCs must be understood and quantified in order to assess photochemical ozone formation in the regions surrounding East Asian megacities. © 2012 Elsevier Ltd.

Abstract: The washout effect of summertime rain on surface air pollutants (O3, CO, NO2, SO2, and PM10) has been investigated over South Korea during 2002–2012 using routinely available air-monitored and meteorological data. Three new washout indices for PM10, SO2, NO2, and CO are developed to express the effect of precipitation scavenging on these pollutants. All of these pollutants show statistically significant negative correlations between their concentrations and rain intensity due to washout or convection. The washout effect is estimated for precipitation episodes classified by rain intensity (one set included all episodes and another included a subset of moderate intensity episodes that exclude Changma and typhoons), based on the log-transformed hourly data. The most sensitive air pollutant to the rain onset among these five air pollutants is PM10. The relative effect of the rainfall washout on the air pollutant concentrations is estimated to be: PM10 > SO2 > NO2 > CO > O3, indicating that PM10 is most effectively scavenged by rainfall. The analysis suggests that the O3 concentrations may increase due to vertical mixing leading to its downward transport from the lower stratosphere/upper troposphere. The concentrations of CO are reduced, probably due to both the washout and convection. The concentrations of NO2 are affected by the opposing influences of lightning-generation and washout and this are discussed as well. [Copyright &y& Elsevier]