A Numerical Analysis of the Changes in O3 Concentration in a Wildfire Plume

Abstract

This study analyzed the characteristics of changes in O3 concentration in a plume induced by a wildfire in Andong, South Korea, from 24 to 26 April 2020, using the Community Multi-scale Air Quality (CMAQ) model. Fire INventory from National Center for Atmospheric Research (FINN) emissions data were used for the wildfire emissions. The increases in the concentrations of primary pollutants (CO, NOx, and volatile organic compounds (VOCs)) due to the wildfire peaked near the source at 09 LST and, as the plume was transported, the reduction in the supply of pollutants from wildfire, as well as chemical reactions, advection and diffusion, and deposition, caused the concentrations to continuously decrease. In contrast, O3 concentration showed a sustained increase during transport due to photochemical reactions caused by precursors (e.g., NOx, VOCs) emitted during the wildfire, peaking (1.40 ppb) at approximately 1 km at 13 LST over 60 km from the source. To analyze these results, a process analysis was conducted. Integrated process rate (IPR) analysis results showed that the production rate of O3 and loss rates of NOx and VOCs peaked at 09 LST due to the photochemical reactions of NOx and VOCs emitted due to wildfire. Then, as the plume was transported, the loss rates of NOx and VOCs that contributed to O3 production continued to decrease at 11 LST. The O3 production rate also decreased at 11 LST but increased at 13 LST due to increasing solar radiation. This indicates that the O3 concentration is complexly determined by O3 precursors and solar radiation. Additionally, IRR analysis revealed that NO and NO2 emitted during wildfire and solar radiation contributed to the production and loss processes of O3; the production reactions of O3 were predominant, and O3 was accumulated and transported in the plume, leading to the peak O3 concentration at 13 LST.