Impact of Aerosol-Cloud Cycling on Aqueous Secondary Organic Aerosol Formation

Chemical processing of organic material in aqueous atmospheric aerosols and cloudwater is known to form secondary organic aerosols (SOA), although the extent to which each of these processes contributes to total aerosol mass is unclear. In this study, we use GAMMA 5.0, a photochemical box model with...

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Bibliographic Details
Published in:Atmosphere 2019-11, Vol.10 (11), p.666
Main Authors: Tsui, William G., Woo, Joseph L., McNeill, V. Faye
Format: Article
Language:English
Subjects:
Aerosol effects
Aerosol formation
Aerosol particles
Aerosols
aqueous aerosol
Atmospheric aerosols
Atmospheric chemistry
Atmospheric models
Chemical reactions
Clouds
cloudwater
Cycles
Humidity
Isoprene
isoprene epoxydiol
Laboratories
Mass transfer
Moisture content
Morphology
Organic acids
Organic coatings
pH effects
Photochemicals
Photochemistry
Secondary aerosols
secondary organic aerosol
Simulation
Time of use
Uptake
Viscosity
Water content
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Summary:Chemical processing of organic material in aqueous atmospheric aerosols and cloudwater is known to form secondary organic aerosols (SOA), although the extent to which each of these processes contributes to total aerosol mass is unclear. In this study, we use GAMMA 5.0, a photochemical box model with coupled gas and aqueous-phase chemistry, to consider the impact of aqueous organic reactions in both aqueous aerosols and clouds on isoprene epoxydiol (IEPOX) SOA over a range of pH for both aqueous phases, including cycling between cloud and aerosol within a single simulation. Low pH aqueous aerosol, in the absence of organic coatings or other morphology which may limit uptake of IEPOX, is found to be an efficient source of IEPOX SOA, consistent with previous work. Cloudwater at pH 4 or lower is also found to be a potentially significant source of IEPOX SOA. This phenomenon is primarily attributed to the relatively high uptake of IEPOX to clouds as a result of higher water content in clouds as compared with aerosol. For more acidic cloudwater, the aqueous organic material is comprised primarily of IEPOX SOA and lower-volatility organic acids. Both cloudwater pH and the time of day or sequence of aerosol-to-cloud or cloud-to-aerosol transitions impacted final aqueous SOA mass and composition in the simulations. The potential significance of cloud processing as a contributor to IEPOX SOA production could account for discrepancies between predicted IEPOX SOA mass from atmospheric models and measured ambient IEPOX SOA mass, or observations of IEPOX SOA in locations where mass transfer limitations are expected in aerosol particles.
ISSN:2073-4433
2073-4433
DOI:10.3390/atmos10110666