An observation-based analysis of atmospheric oxidation capacity in Guangdong, China

Abstract

In this study, an observation-based method (OBM) for evaluating the atmospheric oxidation capacity (AOC) in Guangdong province, China has been developed. We employ the OBM to calculate hydroxyl radical (OH), and in turn to evaluate AOC in seven representative districts/cities in Guangdong province. Three types of AOC are investigated in this study: the commonly defined AOC_ODT which is the rate atmospheric reductants being oxidized; our newly defined AOC_TOX which is the rate atmospheric oxidants being reduced; and the originally suggested AOC_CON which defines the oxidant concentration directly as the AOC index. Key characteristics of these three AOCs are analyzed and compared with each other as well as OH, O3 and NO2 under various atmospheric environments. We found that AOC contributed by OH radicals accounted for the largest portion of total AOC in all three definitions of AOC. In addition, all AOCs were higher during high O3 episodes relative to those of non-episode conditions. More importantly, we found that anthropogenic emissions had enhanced the AOC_CON_OH, or the OH concentration, in the atmosphere surface layer in Guangdong province by a factor of 5.7 over the OH concentration of pre-industrial environment. The corresponding enhancement factor for AOC_TOX_OH was even greater at about 570 because NO2 has increased by about 100 times. The enhancement factor for AOC_ODT_OH was about 30 because constant natural VOC emissions were assumed. This is a highly significant point in terms of the impact of the AOC on human health as well as the ecosystem.