Abstract
Secondary organic aerosol (SOA) is a significant component of atmospheric particulate matter, influencing both air quality and climate. However, SOA simulation in atmospheric models remains highly uncertain due to incomplete knowledge of its formation pathways. Recent research highlights the role of reactive halogens, particularly chlorine, in oxidizing volatile organic compounds (VOCs), triggering SOA formation, and altering other oxidants, thus having a potentially significant effect on SOA, yet their global impact remains underexplored. Isoprene, the most abundant biogenic VOC, is increasingly recognized for its contribution to aqueous-phase SOA via cloud processing, but its global significance is not fully quantified. This thesis addresses these gaps by investigating the impacts of halogen chemistry and isoprene cloud chemistry on global SOA formation using newly developed model schemes within the GEOS-Chem chemical transport model.In chapter 2, we developed a chlorine-SOA simulation within GEOS-Chem model, along with updated anthropogenic continental chlorine emissions. Simulations indicate that chlorine chemistry increases boundary layer SOA by 5–12% over northern hemispheric continents while decreasing SOA by 5–11% over northern Atlantic and Pacific oceans, helping to reduce discrepancies between model results and observations. Notably, the alteration of hydroxyl radicals (OH) and competition between chlorine radicals (Cl) and OH for VOCs dominate the effect of chlorine on SOA, and suppress SOA directly produced from Cl-VOC oxidations. Sensitivity simulations indicate that elevated chlorine can increase SOA by over 100% in polluted regions, with up to 20% of SOA mass consisting of potentially toxic chlorinated organics.
Chapter 3 expands the analysis to the full halogen chemistry by incorporating the bromine-SOA model scheme and bromine and iodine emissions. Results show halogen chemistry amplifies the impact of chlorine chemistry, enhancing SOA by 5–14% over polluted regions but reducing it by 5–20% over marine areas. Anthropogenic halogen emissions contribute about half of this enhancement. High-resolution regional simulations reveal that halogen chemistry can increase wintertime SOA by ~200% in the North China Plain.
Chapter 4 built a new model scheme that represents oxidations and acid-catalyzed chemistry in both aerosol and cloud water. Results demonstrate that in-cloud isoprene SOA formation accounts for ~10% of global SOA, and incorporating salting-out effects improves the vertical simulation of isoprene epoxydiols (IEPOX)-derived SOA by up to 30%.
| Date of Award | 24 Nov 2025 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Xuan WANG (Supervisor) |