Microphysical explanation of the RH-dependent water affinity of biogenic organic aerosol and its importance for climate

N. Rastak, A. Pajunoja, J. C. Acosta Navarro, J. Ma, M. Song, Daniel G. Partridge, A. Kirkevåg, Y. Leong, W. W. Hu, N. F. Taylor, A T Lambe, K. Cerully, A Bougiatioti, P. Liu, R. Krejci, T Petäjä, C. Percival, P. Davidovits, D. R. Worsnop, A. M.L. EkmanA Nenes, S. Martin, J. L. Jimenez, D. R. Collins, D. O. Topping, A. K. Bertram, A. Zuend, A. Virtanen, I. Riipinen

    Research output: Contribution to journalArticlepeer-review

    Abstract

    A large fraction of atmospheric organic aerosol (OA) originates from natural emissions that are oxidized in the atmosphere to form secondary organic aerosol (SOA). Isoprene (IP) and monoterpenes (MT) are the most important precursors of SOA originating from forests. The climate impacts from OA are currently estimated through parameterizations of water uptake that drastically simplify the complexity of OA. We combine laboratory experiments, thermodynamic modeling, field observations, and climate modeling to (1) explain the molecular mechanisms behind RH-dependent SOA water-uptake with solubility and phase separation; (2) show that laboratory data on IP- and MT-SOA hygroscopicity are representative of ambient data with corresponding OA source profiles; and (3) demonstrate the sensitivity of the modeled aerosol climate effect to assumed OA water affinity. We conclude that the commonly used single-parameter hygroscopicity framework can introduce significant error when quantifying the climate effects of organic aerosol. The results highlight the need for better constraints on the overall global OA mass loadings and its molecular composition, including currently underexplored anthropogenic and marine OA sources.

    Original languageEnglish
    Pages (from-to)5167-5177
    JournalGeophysical Research Letters
    Volume44
    Issue number10
    Early online date28 Apr 2017
    DOIs
    Publication statusPublished - 28 Apr 2017

    Keywords

    • Aerosol-climate interactions
    • Aerosol-water interactions
    • Atmospheric aerosol
    • Hygroscopicity
    • Secondary organic aerosol

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