Real Refractive Indices and Formation Yields of Secondary Organic Aerosol Generated from Photooxidation of Limonene and α-Pinene: The Effect of the HC/NOx Ratio
Real Refractive Indices and Formation Yields of Secondary Organic Aerosol Generated from Photooxidation of Limonene and α-Pinene: The Effect of the HC/NOx Ratio
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DOI：
10.1021/jp301302z
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发表时间：
2012-06-21
影响因子：
2.9
通讯作者：
Paulson, Suzanne E.
中科院分区：
文献类型：
--
作者：
Kim, Hwajin;Barkey, Brian;Paulson, Suzanne E.
气溶胶折射率是影响气溶胶光学特性的重要参数，它直接影响气溶胶的直接效应和卫星反演结果。在这里，我们调查的真实的折射率（m（r））的二次有机气溶胶（SOA）从柠檬烯和α-蒎烯的光氧化与不同的HC/NOx的比例。使用平行和垂直偏振的532 nm光结合测得的粒径分布，从极性浊度计数据获得折射率，并使用遗传算法和Mie-Lorenz散射理论进行检索。与磁共振反演相关的绝对误差为+/- 0.03，根据颗粒大小，对于质量浓度高于5-20 μ g/m3的情况，可靠的反演是可能的。柠檬烯SOA的数据表明，最重要的因素控制的折射率是HC/NOx的比例，折射率是不太敏感的气溶胶年龄或质量浓度。对于柠檬烯，折射率的范围为约1.34至1.56，对于α-蒎烯，折射率的范围为1.36至1.52，并且通常随着HC/NOx比的增加而降低。特别是对于柠檬烯，颗粒直径也与HC/NOx比负相关;最终尺寸模式随着HC/NOx比从33降低到6而从220增加到330 nm。在努力探索的能力，从文献中的模型来解释所观察到的折射率，最近的柠檬烯氧化机制相结合的SOA分区和结构性质的关系，用于估计冷凝物种的折射率。所得的折射率下降在一个更窄的范围内（1.475 +/- 0.02）比实验观察到的mr。我们假设实验观察到的高mr值是由于低聚和低值的水吸收，小的可溶性分子，如乙二醛和其他因素，其中每一个都不包括在氧化机制。在质量浓度从6到150 μ g/m3的范围内测量了气溶胶形成量，在此范围内，气溶胶形成量稳定增加，并且在高HC/NOx比实验中更高。
The refractive index is an important property affecting aerosol optical properties, which in turn help determine the aerosol direct effect and satellite retrieval results. Here, we investigate the real refractive indices (m(r)) of secondary organic aerosols (SOA) generated from the photooxidation of limonene and a-pinene with different HC/NOx ratios. Refractive indices were obtained from polar nephelometer data using parallel and perpendicular polarized 532 nm light combined with measured size distributions, and retrievals were performed using a genetic algorithm and Mie-Lorenz scattering theory. The absolute error associated with the mr retrieval is +/- 0.03, and reliable retrievals are possible for mass concentrations above 5-20 mu g/m(3) depending on particle size. The limonene SOA data suggest the most important factor controlling the refractive index is the HC/NOx ratio; the refractive index is much less sensitive to the aerosol age or mass concentration. The refractive index ranges from about 1.34 to 1.56 for limonene and from 1.36 to 1.52, for alpha-pinene, and generally decreases as the HC/NOx ratio increases. Especially for limonene, the particle diameter is also inversely related to the HC/NOx ratio; the final size mode increases from 220 to 330 nm as the HC/NOx ratio decreases from 33 to 6. In an effort to explore the ability of models from the literature to explain the observed refractive indices, a recent limonene oxidation mechanism was combined with SOA partitioning and a structure property relationship for estimating refractive indices of condensing species. The resulting refractive indices fell in a much narrower range (1.475 +/- 0.02) of mr than observed experimentally. We hypothesize the experimentally observed high mr values are due to oligomerization and the low values to water uptake, small soluble molecules such as glyoxal and other factors, each of which is not included in the oxidation mechanism. Aerosol formation yields were measured over the mass concentration range from 6 to similar to 150 mu g/m(3), over which they increased steadily, and were higher for high HC/NOx ratio experiments.