10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Biogenic New Particle Formation: From Pristine to Polluted Environments
LUBNA DADA, Martin Heinritzi, Mario Simon, Chao Yan, Dominik Stolzenburg, Katrianne Lehtipalo, Markku Kulmala, Jasper Kirkby, CLOUD Collaboration, University of Helsinki
Abstract Number: 1192 Working Group: Aerosol Chemistry
Abstract Atmospheric aerosols affect Earth’s radiative energy balance. New particle formation (NPF) by gas-to-particle conversion is estimated to contribute to more than half of global cloud condensation nuclei. Previously, it was thought that NPF can only occur in the presence of sulfuric acid vapour and that ions play only a minor role in the process. However, the CLOUD (Cosmics Leaving OUtdoor Droplets) experiment at CERN has shown that pure biogenic particles can form from organic precursors in the absence of any other vapor, including sulfuric acid (Kirkby et al., Nature 533, 2016), and, moreover, that ions are important to stabilise the embryonic particles. Formation of pure organic particles has also been observed in the real atmosphere, making the phenomenon important for further investigation (Bianchi et al., Science 352, 2016).
Here we present results from CLOUD experiments on pure biogenic NPF and early growth under realistic atmospheric conditions. Our aim is to understand the interactions between the environment and different precursor volatile organic vapours by introducing an individual monoterpene, a sesquiterpene and isoprene, and then combining them to form what we call a biogenic “soup”. Using different concentrations of the biogenic soup at temperatures of -25, 5, 25 oC, we measured the formation and growth rates of pure biogenic particles. We investigated the influence of NOx on the production of the highly oxygenated biogenic molecules (HOMs) responsible for NPF and growth. We also studied the effect of various ionisation rates from zero to natural cosmic rays to the CERN pion beam to demonstrate the different layers of the atmosphere. Finally, in order to understand the boundary between pristine and polluted environments, we added sulfur dioxide and ammonia to the chamber and measured where the transition occurs between pure biogenic- and sulfuric acid-driven nucleation.
Our measurements of pure biogenic nucleation under realistic environmental conditions will help to understand nocturnal NPF in the absence of sulfuric acid, and also of NPF in pristine environments such as during the pre-industrial period or in the Amazon at low and high altitudes.