ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-9113-2012 On the formation of sulphuric acid – amine clusters in varying atmospheric conditions and its influence on atmospheric new particle formation Paasonen P. 1 2 Olenius T. 1 Kupiainen O. 1 Kurtén T. 3 Petäjä T. 1 Birmili W. 4 Hamed A. 5 Hu M. 6 Huey L. G. 7 Plass-Duelmer C. 8 Smith J. N. 5 9 Wiedensohler A. 4 Loukonen V. 1 McGrath M. J. 1 10 Ortega I. K. 1 Laaksonen A. 5 11 Vehkamäki H. 1 Kerminen V.-M. 1 Kulmala M. 1 Department of Physics, University of Helsinki, Helsinki, Finland International Institute for Applied Systems Analysis, Laxenburg, Austria Department of Chemistry, University of Helsinki, Helsinki, Finland Leibniz Institute for Tropospheric Research, Leipzig, Germany Department of Applied Physics, University of Eastern Finland, Kuopio, Finland State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing, China School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, USA Hohenpeissenberg Meteorological Observatory, German Meteorological Service, Germany National Center for Atmospheric Research, Boulder, Colorado, USA Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto, Japan Finnish Meteorological Institute, Helsinki, Finland 05 10 2012 12 19 9113 9133 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/9113/2012/acp-12-9113-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/9113/2012/acp-12-9113-2012.pdf

Sulphuric acid is a key component in atmospheric new particle formation. However, sulphuric acid alone does not form stable enough clusters to initiate particle formation in atmospheric conditions. Strong bases, such as amines, have been suggested to stabilize sulphuric acid clusters and thus participate in particle formation. We modelled the formation rate of clusters with two sulphuric acid and two amine molecules (<i>J</i><sub>A2B2</sub>) at varying atmospherically relevant conditions with respect to concentrations of sulphuric acid ([H<sub>2</sub>SO<sub>4</sub>]), dimethylamine ([DMA]) and trimethylamine ([TMA]), temperature and relative humidity (RH). We also tested how the model results change if we assume that the clusters with two sulphuric acid and two amine molecules would act as seeds for heterogeneous nucleation of organic vapours (other than amines) with higher atmospheric concentrations than sulphuric acid. The modelled formation rates <i>J</i><sub>A2B2</sub> were functions of sulphuric acid concentration with close to quadratic dependence, which is in good agreement with atmospheric observations of the connection between the particle formation rate and sulphuric acid concentration. The coefficients <i>K</i><sub>A2B2</sub> connecting the cluster formation rate and sulphuric acid concentrations as <i>J</i><sub>A2B2</sub>=<i>K</i><sub>A2B2</sub>[H<sub>2</sub>SO<sub>4</sub>]<sup>2</sup> turned out to depend also on amine concentrations, temperature and relative humidity. We compared the modelled coefficients <i>K</i><sub>A2B2</sub> with the corresponding coefficients calculated from the atmospheric observations (<i>K</i><sub>obs</sub>) from environments with varying temperatures and levels of anthropogenic influence. By taking into account the modelled behaviour of <i>J</i><sub>A2B2</sub> as a function of [H<sub>2</sub>SO<sub>4</sub>], temperature and RH, the atmospheric particle formation rate was reproduced more closely than with the traditional semi-empirical formulae based on sulphuric acid concentration only. The formation rates of clusters with two sulphuric acid and two amine molecules with different amine compositions (DMA or TMA or one of both) had different responses to varying meteorological conditions and concentrations of vapours participating in particle formation. The observed inverse proportionality of the coefficient <i>K</i><sub>obs</sub> with RH and temperature agreed best with the modelled coefficient <i>K</i><sub>A2B2</sub> related to formation of a cluster with two H<sub>2</sub>SO<sub>4</sub> and one or two TMA molecules, assuming that these clusters can grow in collisions with abundant organic vapour molecules. In case this assumption is valid, our results suggest that the formation rate of clusters with at least two of both sulphuric acid and amine molecules might be the rate-limiting step for atmospheric particle formation. More generally, our analysis elucidates the sensitivity of the atmospheric particle formation rate to meteorological variables and concentrations of vapours participating in particle formation (also other than H<sub>2</sub>SO<sub>4</sub>).

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