CCN activity and droplet growth kinetics of fresh and aged monoterpene secondary organic aerosol
CCN activity and droplet growth kinetics of fresh and aged monoterpene secondary organic aerosol
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DOI：
10.5194/acp-8-3937-2008
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发表时间：
2008-01-01
影响因子：
6.3
通讯作者：
Pandis, S. N.
中科院分区：
文献类型：
--
作者：
Engelhart, G. J.;Asa-Awuku, A.;Pandis, S. N.
研究了由α -蒎烯和单萜烯（α -蒎烯、β -蒎烯、柠檬烯和3-蒈烯）的混合物臭氧分解产生的二次有机气溶胶（SOA）成为云滴的能力。静态CCN计数器和扫描迁移率CCN分析仪（扫描迁移率粒度仪与连续流量计数器耦合）用于CCN测量。与先前的研究一致，单萜SOA相当活跃，可能是大气中云凝结核（CCN）的良好来源。随着气溶胶继续与氧化剂发生反应，观察到α -蒎烯SOA的CCN活化直径减少了约3纳米小时（-1）。羟基自由基进一步氧化SOA颗粒，从而随着时间的推移增强颗粒的CCN活性。臭氧和单萜烯前体的初始浓度（浓度低于40 ppb）似乎不会影响产生的SOA的活性。科勒理论分析（KTA）用于从雾化过滤器样品中推断出在线和离线采样的SOA的摩尔质量。假设完全溶解度，在线SOA的估计平均摩尔质量为180 +/- 55 g mol(-1)（与现有的SOA形态研究一致）。KTA表明，老化的气溶胶（来自α -蒎烯和混合的单萜烯氧化）主要是水溶性的（约65%）。与（NH4）(2)SO4混合的SOA的CCN活度测量表明，有机可以降低高达10 N m（-1）的表面张力（相对于纯水）。SOA样品的液滴生长动力学与（NH4）(2)SO4相似，除了低过饱和时，SOA往往生长得更慢。假设α -蒎烯和混合单萜SOA的颗粒完全溶解，没有解离成离子，分子量为180 g mol(-1)，密度为1.5 g cm(-3)，水的表面张力，通过简单的Kohler理论，可以模拟出10-15%的α -蒎烯和混合单萜SOA的CCN活化直径。
The ability of secondary organic aerosol (SOA) produced from the ozonolysis of alpha-pinene and monoterpene mixtures (alpha-pinene, beta-pinene, limonene and 3-carene) to become cloud droplets was investigated. A static CCN counter and a Scanning Mobility CCN Analyser (a Scanning Mobility Particle Sizer coupled with a Continuous Flow counter) were used for the CCN measurements. Consistent with previous studies monoterpene SOA is quite active and would likely be a good source of cloud condensation nuclei (CCN) in the atmosphere. A decrease in CCN activation diameter for alpha-pinene SOA of approximately 3 nm hr(-1) was observed as the aerosol continued to react with oxidants. Hydroxyl radicals further oxidize the SOA particles thereby enhancing the particle CCN activity with time. The initial concentrations of ozone and monoterpene precursor (for concentrations lower than 40 ppb) do not appear to affect the activity of the resulting SOA. Kohler Theory Analysis (KTA) is used to infer the molar mass of the SOA sampled online and offline from atomized filter samples. The estimated average molar mass of online SOA was determined to be 180 +/- 55 g mol(-1) (consistent with existing SOA speciation studies) assuming complete solubility. KTA suggests that the aged aerosol (both from alpha-pinene and the mixed monoterpene oxidation) is primarily water-soluble (around 65%). CCN activity measurements of the SOA mixed with (NH4)(2)SO4 suggest that the organic can depress surface tension by as much as 10 N m(-1) (with respect to pure water). The droplet growth kinetics of SOA samples are similar to (NH4)(2)SO4, except at low supersaturation, where SOA tends to grow more slowly. The CCN activation diameter of alpha-pinene and mixed monoterpene SOA can be modelled to within 10-15% of experiments by a simple implementation of Kohler theory, assuming complete dissolution of the particles, no dissociation into ions, a molecular weight of 180 g mol(-1), a density of 1.5 g cm(-3), and the surface tension of water.