Abstract
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.
Highlights
Over the past three decades, the importance of biogenic volatile organic compounds (BVOCs) for tropospheric photochemistry hasS.-Y
The observed CO levels at Taehwa Research Forest (TRF) varied from relatively clean (w200 ppbv) to polluted regimes. This shows that TRF is an ideal observational location to explore the roles BVOCs in regional photochemistry for a wide range of anthropogenic influences
Model simulations suggest that BVOC can enhance daytime ozone concentrations in this region by 5e30 ppbv
Summary
Over the past three decades, the importance of biogenic volatile organic compounds (BVOCs) for tropospheric photochemistry hasS.-Y. Photochemistry of BVOCs in urban environments should be thoroughly studied to address photochemical ozone and secondary organic aerosol (SOA) formation. This consideration is especially critical to study air quality of Asian megacities where urban areas are often near forested regions. In the absence of urban air pollution, BVOCs and natural sources of NOx maintain a level of oxidation capacity that effectively removes reactive toxic gas species and greenhouse gases in the atmosphere (e.g. methane). The elevated level of ozone is harmful to human respiratory systems (Patz et al, 2005). It can cause significant reduction of crop yields Tropospheric ozone along with SOA from tropospheric photochemistry interacts with solar radiation to affect regional and global climate (IPCC, 2007)
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