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Published May 26, 2016 | Published + Supplemental Material
Journal Article Open

The role of low-volatility organic compounds in initial particle growth in the atmosphere

Abstract

About half of present-day cloud condensation nuclei originate from atmospheric nucleation, frequently appearing as a burst of new particles near midday. Atmospheric observations show that the growth rate of new particles often accelerates when the diameter of the particles is between one and ten nanometres. In this critical size range, new particles are most likely to be lost by coagulation with pre-existing particles, thereby failing to form new cloud condensation nuclei that are typically 50 to 100 nanometres across. Sulfuric acid vapour is often involved in nucleation but is too scarce to explain most subsequent growth, leaving organic vapours as the most plausible alternative, at least in the planetary boundary layer. Although recent studies predict that low-volatility organic vapours contribute during initial growth, direct evidence has been lacking. The accelerating growth may result from increased photolytic production of condensable organic species in the afternoon, and the presence of a possible Kelvin (curvature) effect, which inhibits organic vapour condensation on the smallest particles (the nano-Köhler theory), has so far remained ambiguous. Here we present experiments performed in a large chamber under atmospheric conditions that investigate the role of organic vapours in the initial growth of nucleated organic particles in the absence of inorganic acids and bases such as sulfuric acid or ammonia and amines, respectively. Using data from the same set of experiments, it has been shown that organic vapours alone can drive nucleation. We focus on the growth of nucleated particles and find that the organic vapours that drive initial growth have extremely low volatilities (saturation concentration less than 10^(−4.5) micrograms per cubic metre). As the particles increase in size and the Kelvin barrier falls, subsequent growth is primarily due to more abundant organic vapours of slightly higher volatility (saturation concentrations of 10^(−4.5) to 10^(−0.5) micrograms per cubic metre). We present a particle growth model that quantitatively reproduces our measurements. Furthermore, we implement a parameterization of the first steps of growth in a global aerosol model and find that concentrations of atmospheric cloud concentration nuclei can change substantially in response, that is, by up to 50 per cent in comparison with previously assumed growth rate parameterizations.

Additional Information

© 2016 Macmillan Publishers Limited. This work is licensed under a Creative Commons Attribution 4.0 International (CC BY 4.0) licence. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons licence, users will need to obtain permission from the licence holder to reproduce the material. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. Received 01 September 2015; Accepted 22 April 2016; Published online 25 May 2016. We thank CERN for supporting CLOUD with technical and financial resources, and for providing a particle beam from the CERN Proton Synchrotron. This research has received funding from the EC Seventh Framework Programme (Marie Curie Initial Training Network 'CLOUD-ITN' no. 215072, MC-ITN 'CLOUD-TRAIN', no. 316662, and ERC-StG-ATMOGAIN (278277) and ERC-Advanced 'ATMNUCLE' grant no. 227463), the German Federal Ministry of Education and Research (project nos 01LK0902A and 01LK1222A), the Swiss National Science Foundation (project nos 200020_135307, 200020_152907, 20FI20_149002 and 200021_140663), the Academy of Finland Center of Excellence programme (project no. 1118615), the Academy of Finland (CoE project no. 1118615, LASTU project no. 135054), the Nessling Foundation, the Austrian Science Fund (FWF; project no. J3198-N21), the EU's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie (no. 656994), the Swedish Research Council, Vetenskapsrådet (grant no. 2011-5120), the Portuguese Foundation for Science and Technology (project no. CERN/FP/116387/2010), the Presidium of the Russian Academy of Sciences and Russian Foundation for Basic Research (grants 08-02-91006-CERN and 12-02-91522-CERN), Dreyfus Award EP-11-117, the Davidow Foundation, the US National Science Foundation (grants AGS1136479, AGS1447056, AGS1439551 and CHE1012293), US Department of Energy (grant DE-SC00014469) and the FP7 project BACCHUS (grant agreement 603445). Author Contributions: A.A., J.A., U.B., A.-K.B., M.B., F.B., K.S.C., J.S.C., J.C., A.D., J.Do., N.M.D., J.Du., S.E., R.C.F., A.F., C.Fr., C.Fu., R.G., M.G., M.H., T.J., H.K., J.Kir., M.Kr., M.Ku., A.K., A.L., K.L., P.M., U.M., T.N., T.P., F.M.P., M.P.R., S.S., M.Sim., M.Sip., J.N.S., G.S., A.T., J.T., A.V., A.C.W., R.W., E.W., D.W., P.M.W., D.W. and C.Y. designed the experiment or prepared the CLOUD facility or instruments. A.A., J.A., A.-K.B., M.B., F.B., S.B., J.S.C., J.C., A.D., J.Du., S.E., A.F., C.Fr., C.Fu., H.G., M.H., C.R.H., T.J., J.Ka., H.K., J. Kim, J.Kir., M.Kr., A.K., M.L., K.L., P.M., U.M., T.N., F.M.P., I.R., M.P.R., N.S., S.S., K.S., M.Sim., M.Sip., J.N.S., G.S., A.T., J.T., A.V., A.C.W., R.W., C.W., D.W., C.Y. and P.Y. collected data. L.A., A.K.B., F.B., S.B., J.S.C., N.M.D., R.C.F., A.F., C.F., M.H., C.R.H., T.J., K.L., U.M., T.N., N.S., S.S., M.Sim., M.Sip., G.S., J.T., R.W., C.W., D.W. and C.Y. performed data analysis. J.Do. and U.M. contributed HOM structures. W.K.C., N.M.D., L.A., I.R. and J.T. performed aerosol growth modelling. H.G. performed GLOMAP modelling. J.T., L.A., U.B., F.B., K.S.C., J.C., J.Do., N.M.D., J.Du., R.C.F., C.Fr., H.G., M.G., M.H., C.R.H., T.J., J.Kir., M.Ku., K.L., U.M., T.P., I.R., M.P.R., N.S., S.S., M.Sim., C.W., D.W. and C.Y. were involved in the scientific interpretation and discussion. J.T., U.B., J.Do., N.M.D. and H.G. wrote the manuscript. All commented on the paper. The authors declare no competing financial interests.

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