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Measurement report: Closure Analysis of Aerosol–cloud Composition in Tropical Maritime Warm ConvectionCloud droplet chemical composition is a key observable property that can aid understanding of how aerosols and clouds interact. As part of the Clouds, Aerosols and Monsoon Processes – Philippines Experiment (CAMP2Ex), three case studies were analyzed involving collocated airborne sampling of relevant clear and cloudy air masses associated with maritime warm convection. Two of the cases represented a polluted marine background, with signatures of transported East Asian regional pollution, aged over water for several days, while the third case comprised a major smoke transport event from Kalimantan fires.

Sea salt was a dominant component of cloud droplet composition, in spite of fine particulate enhancement from regional anthropogenic sources. Furthermore, the proportion of sea salt was enhanced relative to sulfate in rainwater and may indicate both a propensity for sea salt to aid warm rain production and an increased collection
efficiency of large sea salt particles by rain in subsaturated environments. Amongst cases, as precipitation became more significant, so too did the variability in the sea salt to (non-sea salt) sulfate ratio. Across cases, nitrate and ammonium were fractionally greater in cloud water than fine-mode aerosol particles; however, a strong
covariability in cloud water nitrate and sea salt was suggestive of prior uptake of nitrate on large salt particles.

A mass-based closure analysis of non-sea salt sulfate compared the cloud water air-equivalent mass concentration to the concentration of aerosol particles serving as cloud condensation nuclei for droplet activation. While sulfate found in cloud was generally constrained by the sub-cloud aerosol concentration, there was significant
intra-cloud variability that was attributed to entrainment – causing evaporation of sulfate-containing droplets –and losses due to precipitation. In addition, precipitation tended to promote mesoscale variability in the sub-cloud aerosol through a combination of removal, convective downdrafts, and dynamically driven convergence. Physical
mechanisms exerted such strong control over the cloud water compositional budget that it was not possible to isolate any signature of chemical production/loss using in-cloud observations. The cloud-free environment surrounding the non-precipitating smoke case indicated sulfate enhancement compared to convective mixing quantified by a stable gas tracer; however, this was not observed in the cloud water (either through use of ratios
or the mass closure), perhaps implying that the warm convective cloud timescale was too short for chemical production to be a leading-order budgetary term and because precursors had already been predominantly exhausted.
Closure of other species was truncated by incomplete characterization of coarse aerosol (e.g., it was found that only 10 %–50% of sea salt mass found in cloud was captured during clear-air sampling) and unmeasured gasphase abundances affecting closure of semi-volatile aerosol species (e.g., ammonium, nitrate and organic) and soluble volatile organic compound contributions to total organic carbon in cloud water.
Document ID
20220015631
Acquisition Source
Langley Research Center
Document Type
Accepted Manuscript (Version with final changes)
Authors
Ewan Crosbie
(Science Systems and Applications (United States) Lanham, Maryland, United States)
Luke D Ziemba
(Langley Research Center Hampton, Virginia, United States)
Michael A Shook ORCID
(Langley Research Center Hampton, Virginia, United States)
Claire E Robinson
(Science Systems and Applications (United States) Lanham, Maryland, United States)
Edward L Winstead
(Science Systems and Applications (United States) Lanham, Maryland, United States)
Kenneth L Thornhill
(Science Systems and Applications (United States) Lanham, Maryland, United States)
Rachael Braun
(University of Arizona Tucson, Arizona, United States)
Alexander B MacDonald ORCID
(University of California, Riverside Riverside, California, United States)
Connor Stahl
(University of Arizona Tucson, Arizona, United States)
Armin Sorooshian ORCID
(University of Arizona Tucson, Arizona, United States)
Susan van den Heever ORCID
(Colorado State University Fort Collins, Colorado, United States)
Joshua P DiGangi ORCID
(Langley Research Center Hampton, Virginia, United States)
Glenn S Diskin ORCID
(Langley Research Center Hampton, Virginia, United States)
Sarah Woods ORCID
(Stratton Park Engineering Company (United States) Boulder, Colorado, United States)
Paola Banaga ORCID
(Manila Observatory Quezon City, Philippines)
Matthew D Brown ORCID
(Science Systems and Applications (United States) Lanham, Maryland, United States)
Francesca Gallo ORCID
(Universities Space Research Association Columbia, Maryland, United States)
Miguel Ricardo A Hilario ORCID
(University of Arizona Tucson, Arizona, United States)
Carolyn E Jordan ORCID
(National Institute of Aerospace Hampton, Virginia, United States)
Gabrielle R Leung
(Colorado State University Fort Collins, Colorado, United States)
Richard H Moore ORCID
(Langley Research Center Hampton, Virginia, United States)
Kevin J Sanchez ORCID
(Universities Space Research Association Columbia, Maryland, United States)
Taylor J Shingler
(Langley Research Center Hampton, Virginia, United States)
Elizabeth B Wiggins
(Universities Space Research Association Columbia, Maryland, United States)
Date Acquired
October 18, 2022
Publication Date
October 17, 2022
Publication Information
Publication: Atmospheric Chemistry and Physics
Publisher: Copernicus
Volume: 22
Issue: 20
Issue Publication Date: October 17, 2022
ISSN: 1680-7316
e-ISSN: 1680-7324
Subject Category
Meteorology And Climatology
Funding Number(s)
WBS: 281945.02.80.01.45
CONTRACT_GRANT: 80NSSC18K0149
CONTRACT_GRANT: 80NSSC18K0148
Distribution Limits
Public
Copyright
Portions of document may include copyright protected material.
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