The role of low-volatility organic compounds in initial particle growth in the atmosphere
Authors: Tröstl Jasmin , Chuang Wayne K. , Gordon Hamish , Heinritzi Martin , Yan Chao , Molteni Ugo , Ahlm Lars , Frege Carla , Bianchi Federico , Wagner Robert , Simon Mario , Lehtipalo Katrianne , Williamson Christina , Craven Jill S. , Duplissy Jonathan , Adamov Alexey , Almeida Joao , Bernhammer Anne-Kathrin , Breitenlechner Martin , Brilke Sophia , Dias Antònio , Ehrhart Sebastian , Flagan Richard C. , Franchin Alessandro , Fuchs Claudia , Guida Roberto , Gysel Martin , Hansel Armin , Hoyle Christopher R. , Jokinen Tuija , Junninen Heikki , Kangasluoma Juha , Keskinen Helmi , Kim Jaeseok , Krapf Manuel , Kürten Andreas , Laaksonen Ari , Lawler Michael , Leiminger Markus , Mathot Serge , Möhler Ottmar , Nieminen Tuomo , Onnela Antti , Petäjä Tuukka , Piel Felix M. , Miettinen Pasi , Rissanen Matti P. , Rondo Linda , Sarnela Nina , Schobesberger Siegfried , Sengupta Kamalika , Sipilä Mikko , Smith James N. , Steiner Gerhard , Tomè Antònio , Virtanen Annele , Wagner Andrea C. , Weingartner Ernest , Wimmer Daniela , Winkler Paul M. , Ye Penglin , Carslaw Kenneth S. , Curtius Joachim , Dommen Josef , Kirkby Jasper , Kulmala Markku , Riipinen Ilona , Worsnop Douglas R. , Donahue Neil M. , Baltensperger Urs 
Published: May 2016

About half of present-day cloud condensation nuclei originate from atmospheric nucleation, frequently appearing as a burst of new particles near midday1. Atmospheric observations show that the growth rate of new particles often accelerates when the diameter of the particles is between one and ten nanometres2,3. In this critical size range, new particles are most likely to be lost by coagulation with pre-existing particles4, 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 growth5,6, leaving organic vapours as the most plausible alternative, at least in the planetary boundary layer7,8,9,10. Although recent studies11,12,13 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 afternoon2, and the presence of a possible Kelvin (curvature) effect, which inhibits organic vapour condensation on the smallest particles (the nano-Köhler theory)2,14, 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 shown15 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.