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Sci Total Environ ; 685: 976-985, 2019 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-31390715


Secondary organic aerosol (SOA) species formed in atmospheric aqueous phases is recently recognized as an important contributor to fine aerosols, which is known to be a prominent human health risk factor internationally. This work, for the first time, systematically investigated aqueous-phase photochemical oxidation of 4-ethylphenol (4-EP) - a model compound from biomass burning and a surrogate of intermediate volatility organic compounds, under both ultraviolet (UV) (Hg lamp) and simulated sunlight (Xe lamp). We found that 4-EP could degrade upon hydroxal radical (OH) oxidation under UV light nearly 15 times faster than that under simulated sunlight, but large aqueous SOA (aqSOA) yields (108%-122%) were observed under both situations. AqSOA masses and oxidation states continuously increased under simulated sunlight, yet they increased first then decreased quickly under UV light. We proposed a reaction scheme based on identified products, showing that oligomerization, functionalization and fragmentation all can occur during 4-EP oxidation. Our results demonstrate that OH radical may suppress oligomerization and functionalization, but is favorable for fragmentation. Under UV light with H2O2 (high OH), fragmentation was dominant, producing more volatile and smaller molecules, and less aqSOA in later oxidation; Under simulated sunlight with H2O2 (moderate OH), functionalization that can form hydroxylated monomer was more important. Moreover, 4-EP oxidation by the organic triplet excited state (3C*) could form species with stronger visible light absorptivity than those from OH-mediated oxidation, and the absorptivity showed positive link with contents of humic-like substances.

Huan Jing Ke Xue ; 39(8): 3954-3964, 2018 Aug 08.
Artigo em Chinês | MEDLINE | ID: mdl-29998706


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.