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Secondary Organic Aerosols (SOAs) are fine airborne particles formed from the atmospheric oxidation of VOCs. Gaseous VOCs react with oxidants like [latex]O_3[/latex], [latex]\bullet OH[/latex], or [latex]NO_3\bullet[/latex] to produce low-volatility products. These products can then undergo gas-to-particle conversion, either by forming new particles (nucleation) or condensing onto pre-existing aerosols. SOAs are a major component of PM2.5, impacting climate and human health.
The formation of SOA is a critical but highly complex atmospheric process. It begins with the gas-phase oxidation of a parent VOC, which can be either biogenic (e.g., alpha-pinene) or anthropogenic (e.g., toluene). This initial oxidation step adds functional groups, such as hydroxyl (-OH), carbonyl (=O), and carboxyl (-COOH), to the carbon backbone. These additions decrease the molecule’s volatility (its tendency to remain in the gas phase).
经过一个或多个氧化步骤后，所得产品可能具有足够低的 蒸汽压 to partition into the particle phase. This partitioning is governed by absorptive partitioning theory, where the semi-volatile gas dissolves into an existing organic aerosol phase. Alternatively, if concentrations of very low volatility products are high enough, they can nucleate to form entirely new particles. The chemistry can continue within the aerosol particle itself (aqueous-phase or multiphase chemistry), leading to the formation of even larger, more complex molecules and further increasing the particle’s mass. Because SOAs can scatter and absorb solar radiation and act as cloud condensation nuclei, they play a significant, yet uncertain, role in the Earth’s climate system.
二次有机气溶胶（SOA）
（如果日期未知或不相关，例如“流体力学”，则提供其显著出现的近似估计）
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