Evaluation of the Relative Importance of Radical Sources in Determining the Regional Tropospheric Oxidation Capacity in the Seoul Metropolitan Area

Abstract:

We will discuss oxidation capacity in the boundary layer of the Seoul Metropolitan Area (SMA) by analyzing a comprehensive field observational datasets of trace gases, radicals, and radical precursors. Two intensive field observations will be discussed. From mid-May to mid-June of 2015, we conducted a field observation in the middle of Seoul, representing a region with high anthropogenic emissions and photochemistry near the source region. We deployed an identical suite of instrumentation (i.e., CO, NO_X, O₃, SO₂, VOCs, ClNO₂, HONO, and PANs) at Taehwa Research Forest (TRF), ~ 50 km from the center of Seoul in early September of 2015. The site has been characterized as an ideal region in probing roles of biogenic VOCs (BVOCs) in a moderately polluted regional background. Therefore, the comparisons between two datasets will allow us to assess regional oxidation capacity of a megacity surrounded by forests, which is a typical set-up in the East Asian region. The main focus of the discussion was to investigate the following: (i) relative impact of nighttime radical reservoirs (i.e., HONO and ClNO₂) in the morning radical budget in the urban and suburban environments and (ii) relative importance of unconstrained primary and recycling (e.g., BVOC oxidation) OH production at the isoprene dominated TRF region. An observationally constrained box model with detailed VOC chemical oxidation schemes (e.g., MCM) will be used for the comprehensive evaluations.