Slower CCN growth kinetics of anthropogenic aerosol compared to biogenic aerosol observed at a rural site

Growth rates of water droplets were measured with a static diffusion cloud condensation chamber in May–June 2007 at a rural field site in Southern Ontario, Canada, 70 km north of Toronto. The observations include periods when the winds were from the south and the site was impacted by anthropogenic a...

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Main Authors: N. C. Shantz, R. Y.-W. Chang, J. G. Slowik, A. Vlasenko, J. P. D. Abbatt, W. R. Leaitch
Format: Article
Language:English
Published: Copernicus Publications 2010-01-01
Series:Atmospheric Chemistry and Physics
Online Access:http://www.atmos-chem-phys.net/10/299/2010/acp-10-299-2010.pdf
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spelling doaj-dd98cf90db134471bb572e4ba93e65ea2020-11-25T01:07:36ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242010-01-01101299312Slower CCN growth kinetics of anthropogenic aerosol compared to biogenic aerosol observed at a rural siteN. C. ShantzR. Y.-W. ChangJ. G. SlowikA. VlasenkoJ. P. D. AbbattW. R. LeaitchGrowth rates of water droplets were measured with a static diffusion cloud condensation chamber in May–June 2007 at a rural field site in Southern Ontario, Canada, 70 km north of Toronto. The observations include periods when the winds were from the south and the site was impacted by anthropogenic air from the U.S. and Southern Ontario as well as during a 5-day period of northerly wind flow when the aerosol was dominated by biogenic sources. The growth of droplets on anthropogenic size-selected particles centred at 0.1 μm diameter and composed of approximately 40% organic and 60% ammonium sulphate (AS) by mass, was delayed by on the order of 1 s compared to a pure AS aerosol. Simulations of the growth rate on monodisperse particles indicate that a lowering of the water mass accommodation coefficient from α<sub><i>c</i></sub>=1 to an average of α<sub><i>c</i></sub>=0.04 is needed (assuming an insoluble organic with hygroscopicity parameter, κ<sub>org</sub>, of zero). Simulations of the initial growth rate on polydisperse anthropogenic particles agree best with observations for α<sub><i>c</i></sub>=0.07. In contrast, the growth rate of droplets on size-selected aerosol of biogenic character, consisting of >80% organic, was similar to that of pure AS. Simulations of the predominantly biogenic polydisperse aerosol show agreement between the observations and simulations when κ<sub>org</sub>=0.2 (with upper and lower limits of 0.5 and 0.07, respectively) and α<sub><i>c</i></sub>=1. Inhibition of water uptake by the anthropogenic organic applied to an adiabatic cloud parcel model in the form of a constant low α<sub><i>c</i></sub> increases the number of droplets in a cloud compared to pure AS. If the α<sub><i>c</i></sub> is assumed to increase with increasing liquid water on the droplets, then the number of droplets decreases which could diminish the indirect climate forcing effect. The slightly lower κ<sub>org</sub> in the biogenic case decreases the number of droplets in a cloud compared to pure AS. http://www.atmos-chem-phys.net/10/299/2010/acp-10-299-2010.pdf
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language English
format Article
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author N. C. Shantz
R. Y.-W. Chang
J. G. Slowik
A. Vlasenko
J. P. D. Abbatt
W. R. Leaitch
spellingShingle N. C. Shantz
R. Y.-W. Chang
J. G. Slowik
A. Vlasenko
J. P. D. Abbatt
W. R. Leaitch
Slower CCN growth kinetics of anthropogenic aerosol compared to biogenic aerosol observed at a rural site
Atmospheric Chemistry and Physics
author_facet N. C. Shantz
R. Y.-W. Chang
J. G. Slowik
A. Vlasenko
J. P. D. Abbatt
W. R. Leaitch
author_sort N. C. Shantz
title Slower CCN growth kinetics of anthropogenic aerosol compared to biogenic aerosol observed at a rural site
title_short Slower CCN growth kinetics of anthropogenic aerosol compared to biogenic aerosol observed at a rural site
title_full Slower CCN growth kinetics of anthropogenic aerosol compared to biogenic aerosol observed at a rural site
title_fullStr Slower CCN growth kinetics of anthropogenic aerosol compared to biogenic aerosol observed at a rural site
title_full_unstemmed Slower CCN growth kinetics of anthropogenic aerosol compared to biogenic aerosol observed at a rural site
title_sort slower ccn growth kinetics of anthropogenic aerosol compared to biogenic aerosol observed at a rural site
publisher Copernicus Publications
series Atmospheric Chemistry and Physics
issn 1680-7316
1680-7324
publishDate 2010-01-01
description Growth rates of water droplets were measured with a static diffusion cloud condensation chamber in May–June 2007 at a rural field site in Southern Ontario, Canada, 70 km north of Toronto. The observations include periods when the winds were from the south and the site was impacted by anthropogenic air from the U.S. and Southern Ontario as well as during a 5-day period of northerly wind flow when the aerosol was dominated by biogenic sources. The growth of droplets on anthropogenic size-selected particles centred at 0.1 μm diameter and composed of approximately 40% organic and 60% ammonium sulphate (AS) by mass, was delayed by on the order of 1 s compared to a pure AS aerosol. Simulations of the growth rate on monodisperse particles indicate that a lowering of the water mass accommodation coefficient from α<sub><i>c</i></sub>=1 to an average of α<sub><i>c</i></sub>=0.04 is needed (assuming an insoluble organic with hygroscopicity parameter, κ<sub>org</sub>, of zero). Simulations of the initial growth rate on polydisperse anthropogenic particles agree best with observations for α<sub><i>c</i></sub>=0.07. In contrast, the growth rate of droplets on size-selected aerosol of biogenic character, consisting of >80% organic, was similar to that of pure AS. Simulations of the predominantly biogenic polydisperse aerosol show agreement between the observations and simulations when κ<sub>org</sub>=0.2 (with upper and lower limits of 0.5 and 0.07, respectively) and α<sub><i>c</i></sub>=1. Inhibition of water uptake by the anthropogenic organic applied to an adiabatic cloud parcel model in the form of a constant low α<sub><i>c</i></sub> increases the number of droplets in a cloud compared to pure AS. If the α<sub><i>c</i></sub> is assumed to increase with increasing liquid water on the droplets, then the number of droplets decreases which could diminish the indirect climate forcing effect. The slightly lower κ<sub>org</sub> in the biogenic case decreases the number of droplets in a cloud compared to pure AS.
url http://www.atmos-chem-phys.net/10/299/2010/acp-10-299-2010.pdf
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