Condensed-phase biogenic–anthropogenic interactions with implications for cold cloud formation

Joseph C. Charnawskas; Peter A. Alpert; Andrew T. Lambe; Thomas Berkemeier; Rachel E. O’Brien; Paola Massoli; Timothy B. Onasch; Manabu Shiraiwa; Ryan C. Moffet; Mary K. Gilles; Paul Davidovits; Douglas R. Worsnop; Daniel A. Knopf

doi:10.1039/C7FD00010C

Condensed-phase biogenic–anthropogenic interactions with implications for cold cloud formation

Joseph C. Charnawskas,^a Peter A. Alpert,†^a Andrew T. Lambe,^bc Thomas Berkemeier,^d Rachel E. O’Brien,‡^ef Paola Massoli,^c Timothy B. Onasch,

^bc Manabu Shiraiwa,^g Ryan C. Moffet,^f Mary K. Gilles,^e Paul Davidovits,^b Douglas R. Worsnop^c and Daniel A. Knopf

*^a

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* Corresponding authors

^a Institute for Terrestrial and Planetary Atmospheres, School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, New York, USA
E-mail: Daniel.Knopf@stonybrook.edu

^b Chemistry Department, Boston College, Chestnut Hill, Massachusetts, USA

^c Aerodyne Research Inc., Billerica, Massachusetts, USA

^d School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA

^e Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, USA

^f Department of Chemistry, University of the Pacific, Stockton, California, USA

^g Department of Chemistry, University of California, Irvine, California, USA

Abstract

Anthropogenic and biogenic gas emissions contribute to the formation of secondary organic aerosol (SOA). When present, soot particles from fossil fuel combustion can acquire a coating of SOA. We investigate SOA–soot biogenic–anthropogenic interactions and their impact on ice nucleation in relation to the particles’ organic phase state. SOA particles were generated from the OH oxidation of naphthalene, α-pinene, longifolene, or isoprene, with or without the presence of sulfate or soot particles. Corresponding particle glass transition (T_g) and full deliquescence relative humidity (FDRH) were estimated using a numerical diffusion model. Longifolene SOA particles are solid-like and all biogenic SOA sulfate mixtures exhibit a core–shell configuration (i.e. a sulfate-rich core coated with SOA). Biogenic SOA with or without sulfate formed ice at conditions expected for homogeneous ice nucleation, in agreement with respective T_g and FDRH. α-pinene SOA coated soot particles nucleated ice above the homogeneous freezing temperature with soot acting as ice nuclei (IN). At lower temperatures the α-pinene SOA coating can be semisolid, inducing ice nucleation. Naphthalene SOA coated soot particles acted as ice nuclei above and below the homogeneous freezing limit, which can be explained by the presence of a highly viscous SOA phase. Our results suggest that biogenic SOA does not play a significant role in mixed-phase cloud formation and the presence of sulfate renders this even less likely. However, anthropogenic SOA may have an enhancing effect on cloud glaciation under mixed-phase and cirrus cloud conditions compared to biogenic SOA that dominate during pre-industrial times or in pristine areas.

This article is part of the themed collection: Atmospheric chemistry in the Anthropocene

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Condensed-phase biogenic–anthropogenic interactions with implications for cold cloud formation

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