Bulk and molecular-level characterization of laboratory-aged biomass burning organic aerosol from oak leaf and heartwood fuels
Bulk and molecular-level characterization of laboratory-aged biomass burning organic aerosol from oak leaf and heartwood fuels
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DOI：
10.5194/acp-18-2199-2018
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发表时间：
2018-02-15
影响因子：
6.3
通讯作者：
Williams, Brent J.
中科院分区：
文献类型：
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作者：
Fortenberry, Claire F.;Walker, Michael J.;Williams, Brent J.
生物质燃烧有机气溶胶（BBOA）的化学复杂性大大增加了在大气中的光化学老化，有必要控制实验室研究，以告知现场观测。在这些实验中，BBOA从美国白色橡树（栎alba）叶和心材样品中产生的定制的排放和燃烧室和光化学老化的潜在的气溶胶质量（PAM）流反应器。热解吸气溶胶气相色谱仪（TAG）与高分辨率飞行时间气溶胶质谱仪（AMS）并行使用，以分析BBOA在不同水平的光化学老化的化学组成。个别化合物进行了鉴定和整合，以获得关键分子的相对衰变率。一个最近开发的色谱分箱正矩阵因子分解（PMF）技术被用来获得的TAG BBOA色谱图中的因素，提高分析效率，并提供了一个更完整的测定未解决的复杂混合物（UCM）成分的质谱图。此外，最近表征的TAG分解窗口用于跟踪样品解吸期间热不稳定BBOA分解产生的分子片段。我们证明，虽然大多数主要（新鲜排放）BBOA化合物耗尽与光化学老化，某些组件内的TAG热分解窗口洗脱，而不是增强。具体地，分解m/z 44信号（CO2+）的增加趋势表明在PAM反应器中形成二次有机气溶胶（SOA）。源m/z 60（C2 H4 O2+），通常归因于新鲜排放的BBOA在AMS现场测量，也进行了调查。从TAG化学形态和分解窗口数据，我们观察到由于脱水糖（包括左旋葡聚糖）和其他化合物的衰变，随着光化学老化，m/z 60降低，以及由于PAM反应器内热不稳定有机酸的形成，其在TAG样品解吸期间分解，m/z 60增加。当老化两种类型的BBOA（叶和心材），AMS数据表现出这两个贡献的影响，导致有限的变化，以整体m/z 60信号的组合。我们的观测结果表明，在充分了解大量的气溶胶测量AMS在实验室和现场研究中提供的化学形态的数据的重要性。
The chemical complexity of biomass burning organic aerosol (BBOA) greatly increases with photochemical aging in the atmosphere, necessitating controlled laboratory studies to inform field observations. In these experiments, BBOA from American white oak (Quercus alba) leaf and heartwood samples was generated in a custom-built emissions and combustion chamber and photochemically aged in a potential aerosol mass (PAM) flow reactor. A thermal desorption aerosol gas chromatograph (TAG) was used in parallel with a high-resolution time-of-flight aerosol mass spectrometer (AMS) to analyze BBOA chemical composition at different levels of photochemical aging. Individual compounds were identified and integrated to obtain relative decay rates for key molecules. A recently developed chromatogram binning positive matrix factorization (PMF) technique was used to obtain mass spectral profiles for factors in TAG BBOA chromatograms, improving analysis efficiency and providing a more complete determination of unresolved complex mixture (UCM) components. Additionally, the recently characterized TAG decomposition window was used to track molecular fragments created by the decomposition of thermally labile BBOA during sample desorption. We demonstrate that although most primary (freshly emitted) BBOA compounds deplete with photochemical aging, certain components eluting within the TAG thermal decomposition window are instead enhanced. Specifically, the increasing trend in the decomposition m/z 44 signal (CO2+) indicates formation of secondary organic aerosol (SOA) in the PAM reactor. Sources of m/z 60 (C2H4O2+), typically attributed to freshly emitted BBOA in AMS field measurements , were also investigated. From the TAG chemical speciation and decomposition window data, we observed a decrease in m/z 60 with photochemical aging due to the decay of anhydrosugars (including levoglucosan) and other compounds , as well as an increase in m/z 60 due to the formation of thermally labile organic acids within the PAM reactor, which decompose during TAG sample desorption. When aging both types of BBOA (leaf and heartwood), the AMS data exhibit a combination of these two contributing effects, causing limited change to the overall m/z 60 signal. Our observations demonstrate the importance of chemically speciated data in fully understanding bulk aerosol measurements provided by the AMS in both laboratory and field studies.