Explicit modeling of isoprene chemical processing in polluted air masses in suburban areas of the Yangtze River Delta region: radical cycling and formation of ozone and formaldehyde

摘要

In recent years, ozone pollution has become one of the most severe environmental problems in China. Evidence from observations have showed increased frequency of high O 3 levels in suburban areas of the Yangtze River Delta (YRD) region. To better understand the formation mechanism of local O 3 pollution and investigate the potential role of isoprene chemistry in the budgets of RO x ( OH + HO 2 + RO 2 ) radicals, synchronous observations of volatile organic compounds (VOCs), formaldehyde (HCHO), and meteorological parameters were conducted at a suburban site of the YRD region in 2018. Five episodes with elevated O 3 concentrations under stagnant meteorological conditions were identified; an observation-based model (OBM) with the Master Chemical Mechanism was applied to analyze the photochemical processes during these high O 3 episodes. The high levels of O 3 , nitrogen oxides (NO x ), and VOCs facilitated strong production and recycling of RO x radicals with the photolysis of oxygenated VOCs (OVOCs) being the primary source. Our results suggest that local biogenic isoprene is important in suburban photochemical processes. Removing isoprene could drastically slow down the efficiency of RO x recycling and reduce the concentrations of RO x . In addition, the absence of isoprene chemistry could further lead to a decrease in the daily average concentrations of O 3 and HCHO by 34?% and 36?%, respectively. Therefore, this study emphasizes the importance of isoprene chemistry in the suburban atmosphere, particularly with the participation of anthropogenic NO x . Moreover, our results provide insights into the radical chemistry that essentially drives the formation of secondary pollutants (e.g., O 3 and HCHO) in suburban areas of the YRD region.