Anthropogenic organic aerosol in Europe produced mainly through second-generation oxidation
Mao Xiao, Mingyi Wang, Bernhard Mentler, Olga Garmаsh, Houssni Lamkaddam, Ugo Molteni, Mario Simon, Lauri Ahonen, A. Amorim, Andrea Baccarini, Paulus S. Bauer, Dexian Chen, Randall Chiu, Lubna Dada, Jonathan Duplissy, Henning Finkenzeller, Lukas Fischer, Xu‐Cheng He, Martin Heinritzi, Victoria Hofbauer, Changhyuk Kim, Andreas Kürten, А. Н. Квашнин, Katrianne Lehtipalo, Yuliang Liu, Huajun Mai, В. С. Махмутов, Serge Mathot, Roy L. Mauldin, Antti Onnela, Tuukka Petäjä, Lauriane L. J. Quéléver, Matti Rissanen, Simone Schuchmann, Mikko Sipilä, Dominik Stolzenburg, Yuri Stozhkov, Christian Tauber, António Tomé, Robert Wagner, Chao Yan, Boxing Yang, Penglin Ye, Qiaozhi Zha, Joachim Curtius, Armin Hansel, J. Kirkby, Markku Kulmala, Rainer Volkamer, Paul M. Winkler, Douglas R. Worsnop, Wei Nie, Neil M. Donahue, C. R. Hoyle, Jianhui Jiang, Urs Baltensperger, Josef Dommen, Imad El Haddad
Abstract
Exposure to anthropogenic atmospheric aerosol is a major health issue, causing several million deaths per year worldwide. The oxidation of aromatic hydrocarbons from traffic and wood combustion is an important anthropogenic source of low-volatility species in secondary organic aerosol, especially in heavily polluted environments. It is not yet established whether the formation of anthropogenic secondary organic aerosol involves mainly rapid autoxidation, slower sequential oxidation steps or a combination of the two. Here we reproduced a typical urban haze in the 'Cosmics Leaving Outdoor Droplets' chamber at the European Organization for Nuclear Research and observed the dynamics of aromatic oxidation products during secondary organic aerosol growth on a molecular level to determine mechanisms underlying their production and removal. We demonstrate that sequential oxidation is required for substantial secondary organic aerosol formation. Second-generation oxidation decreases the products' saturation vapour pressure by several orders of magnitude and increases the aromatic secondary organic aerosol yields from a few percent to a few tens of percent at typical atmospheric concentrations. Through regional modelling, we show that more than 70% of the exposure to anthropogenic organic aerosol in Europe arises from second-generation oxidation.