气溶胶水相反应生成二次有机气溶胶研究进展

液态水(云滴、雾滴和气溶胶水)在大气中无处不在,为大气水相化学反应提供了重要的场所.气态前体物(主要是VOCs)或它的气相初级氧化产物(包括中/半挥发性有机物,I/SVOCs)在大气凝聚相(水相)中发生反应,形成低挥发性高氧化性有机物(如有机硫和有机氮等),水分蒸发后留在颗粒相,即为水相二次有机气溶胶(aqueous-phase secondary organic aerosol,aq SOA).因其对OA具有重要的贡献和显著的环境、气候和人体健康影响,近年来成为大气化学研究的热点.尽管aq SOA的研究已取得了一些进展,但由于aq SOA形成机制复杂,对aq SOA的认知还比较匮乏.本文重点关注气溶胶水中反应生成的二次有机气溶胶(aqueous aerosol SOA,aa SOA)相关的研究进展,包括气态前体物、形成机制、实验室模拟、外场观测及有关aa SOA产率及贡献的相关研究成果.同时,对aa SOA的来源、生成机制等研究的发展方向进行了展望,包括:未知aa SOA前体物及示踪物鉴别、有机光敏剂诱发的自由基化学、有机硫和有机氮的形成机制、实际气溶胶水溶性组分和外场观测研究、模式模型研究等.

Secondary Organic Aerosols from Aqueous Reaction of Aerosol Water

Liquid water (cloud/fog droplets and aerosols) is ubiquitous in the atmosphere and can provide an important reaction media for aqueous-phase chemical reactions. Gaseous precursors (mainly VOCs) or their gas-phase initial or first-generation oxidation products (including intermediate-volatility and semi-volatile organic compounds; I/SVOCs) can undergo chemical reactions in the atmospheric condensed phase (aqueous phase) to form low-volatility, highly oxidized organic matter[e.g., some key tracer species such as organosulfates (OSs) and organonitrogens (ONs)]. These products largely remain in the particle phase upon water evaporation and are referred to as aqueous secondary organic aerosols (aqSOAs). aqSOAs have been emerging as a research hot topic in atmospheric chemistry, as they can contribute significantly to OAs and thus have important impacts on the environment, climate, and human health. Despite considerable progress, so far, aqSOAs remain poorly understood owing to their complex formation mechanisms. In this review, we focus mainly on the relevant research results on the SOAs formed in aerosol water-aqueous aerosol SOAs (aaSOAs)-including gas-phase precursors, formation mechanisms, laboratory simulations, and field observations, as well as SOA yield and contribution to OAs. Meanwhile, we propose future directions regarding studies of sources and formation mechanisms of aaSOAs, including identification of unknown aaSOA precursors and tracer products, photosensitizer-triggered radical chemistry, formation pathways of OS and ON compounds, field observations and model simulations of aaSOAs.