Presentation Information
[AAS08-P49]Mechanisms of Secondary Organic Aerosol Formation Driven by Enhanced Emissions of Biogenic VOCs during a Typhoon
*Nikita Komuta1,2,3, Mizuo Kajino2,1, Yoshiteru Iinuma4, Takemitsu Arakaki3 (1.University of Tsukuba, 2.Meteorological Research Institute, 3.University of the Ryukyus, 4.Okinawa Institute of Science and Technology)
Keywords:
Atmospheric Chemistry,Aerosols,Typhoon,Air Pollution,BVOCs,Climate Change
Introduction. Biogenic volatile organic compounds (BVOCs) emitted from plants generate biogenic secondary organic aerosols (BSOA) through atmospheric oxidation, affecting health and climate1). BVOC emission rates are high in Okinawa Island, which has high forest coverage, solar radiation, and temperature. On the other hand, BSOA concentrations are relatively low due to low concentrations of oxidants such as O3 2). In contrast, a previous study3) showed that typhoon passage enhanced oxidant transport from East Asia and BVOC emissions due to tree damage, increasing BSOA concentration and oxidation state by using field measurements and the Japan Meteorological Agency's regional meteorology - chemistry model (NHM-Chem)4). However, NHM-Chem did not include SOA chemistry, and so the model analysis focused mainly on O3. Therefore, discussions on BSOA were limited based on observational results, and the BSOA formation mechanism during typhoon events remains unclear. Thus, this study aimed to elucidate BSOA formation processes during typhoon events by constructing a box model that includes BSOA chemistry.
Methods. We employed a box model incorporating the SOA chemistry scheme that includes gas-phase photochemistry, heterogeneous reactions, and gas-particle equilibrium partitioning processes implemented in CMAQ v5.55). Hourly simulation results of gas and aerosol components except SOA obtained from NHM-Chem at OIST (26.47°N, 127.83°E) 3) were used as initial conditions for the box model simulation, and hourly BSOA production rates were obtained after 1 h time integration of the model. The NHM-Chem model domain covers Northeast Asia with 30 km horizontal grid resolution and a 6 km nested grid over Okinawa region, and the simulation period was from June 26 to September 1, 2023. Additionally, sensitivity experiments were conducted by increasing BVOC initial concentrations by constant factors after typhoon passage to evaluate the impact of emission enhancements caused by tree damage.
Results and Discussion. NHM-Chem simulations showed increased concentrations of oxidants such as O3 and NO3 during typhoon passage, and the box model simulations indicated that BSOA production rates increased from an average of 1.79×10-2 µg m-3 h-1 before passage to 7.01×10-2 µg m-3 h-1 after passage (Figure 1). In the BVOC sensitivity experiments, BSOA production increased nonlinearly with BVOC emissions (for example, 15 times BVOC concentrations led to approximately 50 times increase in BSOA production rates). This was because particle-phase fractions of high-volatility BSOA became larger as the particle-phase OA concentrations increased, which resulted in nonlinear enhancement of BSOA formation rates. (Production rates of low-volatility BSOA were insensitive to OA mass, and they were consistently partitioned into the particle phase.) Additionally, before passage, nighttime BSOA formation was negligible, and daytime formation was dominated by low oxidation state monoterpene-derived BSOA. In contrast, after passage, the contribution of high oxidation state isoprene-derived BSOA production increased during daytime, and with increasing NO3 concentrations, formation of monoterpene-derived organic nitrates progressed at night. As a result, the average oxidation state of the BSOA produced increased. These results reproduce observational trends reported previously3) and suggest BSOA formation mechanisms during the typhoon event. This study provides a basis for quantitatively assessing atmospheric pollution risks during typhoons that are expected to intensify and occur more frequently under global warming.
References. 1) Zhao, B., et al. (2025) Chem. Res. Toxicol. 38, 1585-1594. 2) Chatani, S., et al. (2015) Atmos. Environ. 120, 38-50. 3) Iinuma, Y. and Kajino, M. (2025) Earth Space Chem. 9, 699-714. 4) Kajino, M., et al. (2019) J. Meteor. Soc. Jpn. 97(2), 337-374. 5) U.S. EPA. (2024). Community Multiscale Air Quality (CMAQ) model, version 5.5.
Methods. We employed a box model incorporating the SOA chemistry scheme that includes gas-phase photochemistry, heterogeneous reactions, and gas-particle equilibrium partitioning processes implemented in CMAQ v5.55). Hourly simulation results of gas and aerosol components except SOA obtained from NHM-Chem at OIST (26.47°N, 127.83°E) 3) were used as initial conditions for the box model simulation, and hourly BSOA production rates were obtained after 1 h time integration of the model. The NHM-Chem model domain covers Northeast Asia with 30 km horizontal grid resolution and a 6 km nested grid over Okinawa region, and the simulation period was from June 26 to September 1, 2023. Additionally, sensitivity experiments were conducted by increasing BVOC initial concentrations by constant factors after typhoon passage to evaluate the impact of emission enhancements caused by tree damage.
Results and Discussion. NHM-Chem simulations showed increased concentrations of oxidants such as O3 and NO3 during typhoon passage, and the box model simulations indicated that BSOA production rates increased from an average of 1.79×10-2 µg m-3 h-1 before passage to 7.01×10-2 µg m-3 h-1 after passage (Figure 1). In the BVOC sensitivity experiments, BSOA production increased nonlinearly with BVOC emissions (for example, 15 times BVOC concentrations led to approximately 50 times increase in BSOA production rates). This was because particle-phase fractions of high-volatility BSOA became larger as the particle-phase OA concentrations increased, which resulted in nonlinear enhancement of BSOA formation rates. (Production rates of low-volatility BSOA were insensitive to OA mass, and they were consistently partitioned into the particle phase.) Additionally, before passage, nighttime BSOA formation was negligible, and daytime formation was dominated by low oxidation state monoterpene-derived BSOA. In contrast, after passage, the contribution of high oxidation state isoprene-derived BSOA production increased during daytime, and with increasing NO3 concentrations, formation of monoterpene-derived organic nitrates progressed at night. As a result, the average oxidation state of the BSOA produced increased. These results reproduce observational trends reported previously3) and suggest BSOA formation mechanisms during the typhoon event. This study provides a basis for quantitatively assessing atmospheric pollution risks during typhoons that are expected to intensify and occur more frequently under global warming.
References. 1) Zhao, B., et al. (2025) Chem. Res. Toxicol. 38, 1585-1594. 2) Chatani, S., et al. (2015) Atmos. Environ. 120, 38-50. 3) Iinuma, Y. and Kajino, M. (2025) Earth Space Chem. 9, 699-714. 4) Kajino, M., et al. (2019) J. Meteor. Soc. Jpn. 97(2), 337-374. 5) U.S. EPA. (2024). Community Multiscale Air Quality (CMAQ) model, version 5.5.