Brown Carbon Formation from Nighttime Chemistry of Unsaturated Heterocyclic Volatile Organic Compounds,Environmental Science & Technology Letters

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Brown Carbon Formation from Nighttime Chemistry of Unsaturated Heterocyclic Volatile Organic Compounds
Environmental Science & Technology Letters ( IF 8.9 ) Pub Date : 2019-02-05 , DOI: 10.1021/acs.estlett.9b00017
Huanhuan Jiang ₁ , Alexander L. Frie ₁ , Avi Lavi ₂ , Jin Y. Chen ₃ , Haofei Zhang _{2,

3} , Roya Bahreini _{1,

2,

3} , Ying-Hsuan Lin _{1,

3}

Affiliation

Nighttime atmospheric processing enhances the formation of brown carbon aerosol (BrC) in biomass burning plumes. Heterocyclic compounds, a group of volatile organic compounds (VOCs) abundant in biomass burning smoke, are possible BrC sources. Here, we investigated the nitrate radical (NO₃)-initiated oxidation of three unsaturated heterocyclic compounds (pyrrole, furan, and thiophene) as a source of BrC. The imaginary component of the refractive index at 375 nm (k₃₇₅), the single scattering albedo at 375 nm (SSA₃₇₅), and average mass absorption coefficients (⟨MAC⟩_{290–700 nm}) of the resulting secondary organic aerosol (SOA) are reported. Compared to furan and thiophene, NO₃ oxidation of pyrrole has the highest SOA yield. Pyrrole SOA (k₃₇₅ = 0.015 ± 0.003, SSA = 0.86 ± 0.01, ⟨MAC⟩_{290–700 nm} = 3400 ± 700 cm² g^–1) is also more absorbing than furan SOA (⟨MAC⟩_{290–700 nm} = 1100 ± 200 cm² g^–1) and thiophene SOA (k₃₇₅ = 0.003 ± 0.002, SSA₃₇₅ = 0.98 ± 0.01, ⟨MAC⟩_{290–700 nm} = 3000 ± 500 cm² g^–1). Compared to other SOA systems, MACs reported in this study are higher than those from biogenic precursors and similar to high-NO_x anthropogenic SOA. Characterization of SOA molecular composition using high-resolution mass spectrometric measurements revealed unsaturated heterocyclic nitro products or organonitrates as possible chromophores in BrC from all three precursors. These findings reveal nighttime oxidation of fire-sourced heterocyclic compounds, particularly pyrrole, as a plausible source of BrC.

中文翻译：

不饱和杂环挥发性有机化合物夜间化学过程中形成的褐碳

夜间大气处理会增强生物质燃烧烟羽中棕色碳气溶胶（BrC）的形成。杂环化合物可能是BrC的来源，杂环化合物是在燃烧生物质的烟雾中丰富的一组挥发性有机化合物（VOC）。在这里，我们研究了作为BrC来源的三种不饱和杂环化合物（吡咯，呋喃和噻吩）的硝酸根（NO ₃）引发的氧化。所产生的二次有机气溶胶（SOA）在375 nm（k ₃₇₅）处的折射率的虚部，在375 nm（SSA ₃₇₅）处的单散射反照率和平均质量吸收系数（_{⟨MAC⟩290–700 nm}）被报道。与呋喃和噻吩相比，NO ₃吡咯的氧化具有最高的SOA产量。吡咯SOA（k ₃₇₅ = 0.015±0.003，SSA = 0.86±0.01，⟨MAC⟩290–700 _nm = 3400±700 cm ² g ^–1）也比呋喃SOA（_{⟨MAC⟩290–700 nm} = 1100 ）更具吸收性±200 cm ² g ^–1）和噻吩SOA（k ₃₇₅ = 0.003±0.002，SSA ₃₇₅ = 0.98±0.01，_{⟨MAC⟩290–700 nm} = 3000±500 cm ² g ^–1）。相比于其他的SOA系统，MAC的报道在这项研究比那些从生物前体高和类似的高NO _X人为的SOA。使用高分辨率质谱测量法对SOA分子组成进行表征，发现来自所有这三种前体的BrC中的不饱和杂环硝基产物或有机硝酸盐可能是发色团。这些发现揭示了火源杂环化合物（特别是吡咯）在夜间的氧化作用，认为这可能是BrC的来源。

更新日期：2019-02-07

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