On the roles of sulphuric acid and low-volatility organic vapours in the initial steps of atmospheric new particle formation
On the roles of sulphuric acid and low-volatility organic vapours in the initial steps of atmospheric new particle formation
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DOI：
10.5194/acp-10-11223-2010
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发表时间：
2010-01-01
影响因子：
6.3
通讯作者：
Kulmala, M.
中科院分区：
文献类型：
--
作者：
Paasonen, P.;Nieminen, T.;Kulmala, M.
硫酸和有机蒸气已被确定为大气中普遍存在的二次新颗粒形成的关键成分。为了评估它们的相对贡献和空间变异性，我们分析了2007-2009年EUCAARI活动期间在欧洲四个测量点观测到的总共36个新的粒子形成事件。我们测试了几种不同成核机制的模型，这些模型将中性粒子(J)的形成速度与凝结在4 nm以下粒子上的硫酸([H_2SO_4])或低挥发性有机蒸气([org])的浓度或两者的组合结合在一起。此外，我们还确定了中性成核速率J与每个机理中的蒸汽浓度之间的相关成核系数。这项研究的主要目的是确定新颗粒形成和随后生长的机制，使模型成核率和测量成核率之间的差异最小化。在四个测量点中的三个--Hyytiala(芬兰)、Melbitz(德国)和San Pietro Capofiume(意大利)--成核率与硫酸浓度的平方密切相关，而在Hohenpeissenberg(德国)，观察到低挥发性有机蒸气占主导地位。然而，硫酸优势中心的成核速率不能用硫酸浓度和成核系数的单一值来描述，如K in J=K[H_2SO_4](2)，但不同中心的中值系数在一个数量级上存在差异。当假设除单独的H_2SO_4均相成核外，还发生了H_2SO_4和有机蒸气之间的异分子均相成核，即J=K-SA1[H_2SO_4](2)+K-SA_2[H_2SO_4][org]时，这种位置间的差异要小得多。通过在这个方程式中加入一个描述大分子有机蒸气成核的术语K-S3[org](2)，得到了同样好的结果。总体而言，我们的结果表明，有机蒸气确实发挥了作用，不仅在颗粒的凝聚生长中，而且在成核过程中也起到了作用，而且作用的程度因地点而异。
Sulphuric acid and organic vapours have been identified as the key components in the ubiquitous secondary new particle formation in the atmosphere. In order to assess their relative contribution and spatial variability, we analysed altogether 36 new particle formation events observed at four European measurement sites during EUCAARI campaigns in 2007-2009. We tested models of several different nucleation mechanisms coupling the formation rate of neutral particles (J) with the concentration of sulphuric acid ([H2SO4]) or low-volatility organic vapours ([org]) condensing on sub-4 nm particles, or with a combination of both concentrations. Furthermore, we determined the related nucleation coefficients connecting the neutral nucleation rate J with the vapour concentrations in each mechanism. The main goal of the study was to identify the mechanism of new particle formation and subsequent growth that minimizes the difference between the modelled and measured nucleation rates. At three out of four measurement sites - Hyytiala (Finland), Melpitz (Germany) and San Pietro Capofiume (Italy) - the nucleation rate was closely connected to squared sulphuric acid concentration, whereas in Hohenpeissenberg (Germany) the low-volatility organic vapours were observed to be dominant. However, the nucleation rate at the sulphuric acid dominant sites could not be described with sulphuric acid concentration and a single value of the nucleation coefficient, as K in J=K [H2SO4](2), but the median coefficients for different sites varied over an order of magnitude. This inter-site variation was substantially smaller when the heteromolecular homogenous nucleation between H2SO4 and organic vapours was assumed to take place in addition to homogenous nucleation of H2SO4 alone, i.e., J=K-SA1[H2SO4](2)+K-SA2[H2SO4][org]. By adding in this equation a term describing homomolecular organic vapour nucleation, K-s3[org](2), equally good results were achieved. In general, our results suggest that organic vapours do play a role, not only in the condensational growth of the particles, but also in the nucleation process, with a site-specific degree.