Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, The University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States.
Environ Sci Technol. 2014 Oct 21;48(20):12012-21. doi: 10.1021/es503142b. Epub 2014 Oct 6.
Secondary organic aerosol (SOA) produced from reactive uptake and multiphase chemistry of isoprene epoxydiols (IEPOX) has been found to contribute substantially (upward of 33%) to the fine organic aerosol mass over the Southeastern U.S. Brown carbon (BrC) in rural areas of this region has been linked to secondary sources in the summer when the influence of biomass burning is low. We demonstrate the formation of light-absorbing (290 < λ < 700 nm) SOA constituents from reactive uptake of trans-β-IEPOX onto preexisting sulfate aerosols as a potential source of secondary BrC. IEPOX-derived BrC generated in controlled chamber experiments under dry, acidic conditions has an average mass absorption coefficient of ∼ 300 cm(2) g(-1). Chemical analyses of SOA constituents using UV-visible spectroscopy and high-resolution mass spectrometry indicate the presence of highly unsaturated oligomeric species with molecular weights separated by mass units of 100 (C5H8O2) and 82 (C5H6O) coincident with the observations of enhanced light absorption, suggesting such oligomers as chromophores, and potentially explaining one source of humic-like substances (HULIS) ubiquitously present in atmospheric aerosol. Similar light-absorbing oligomers were identified in fine aerosol collected in the rural Southeastern U.S., supporting their atmospheric relevance and revealing a previously unrecognized source of oligomers derived from isoprene that contributes to ambient fine aerosol mass.
次生有机气溶胶 (SOA) 是由异戊二烯环氧化合物 (IEPOX) 的反应性吸收和多相化学产生的，已被发现对美国东南部的细有机气溶胶质量有很大贡献（超过 33%）。该地区农村地区的棕色碳 (BrC) 与夏季生物质燃烧影响较低时的二次源有关。我们证明了反式-β-IEPOX 对预先存在的硫酸盐气溶胶的反应性吸收形成光吸收（290 < λ < 700 nm）SOA 成分，这是次生 BrC 的潜在来源。在干燥、酸性条件下进行的受控室实验中生成的 IEPOX 衍生 BrC 的平均质量吸收系数约为 300 cm(2) g(-1)。使用紫外可见光谱和高分辨率质谱对 SOA 成分进行的化学分析表明，存在高度不饱和的低聚物物种，分子量相差 100（C5H8O2）和 82（C5H6O）质量单位，与增强的光吸收观察结果一致，表明这些低聚物是发色团，并可能解释了普遍存在于大气气溶胶中的腐殖质样物质 (HULIS) 的一个来源。在美国东南部农村地区收集的细颗粒气溶胶中也鉴定出了类似的光吸收低聚物，这支持了它们在大气中的相关性，并揭示了一种以前未被认识到的异戊二烯衍生低聚物来源，这些低聚物对环境细颗粒质量有贡献。
