Physics
Scientific paper
May 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006georl..3310816k&link_type=abstract
Geophysical Research Letters, Volume 33, Issue 10, CiteID L10816
Physics
27
Atmospheric Composition And Structure: Aerosols And Particles (0345, 4801, 4906), Atmospheric Composition And Structure: Cloud Physics And Chemistry, Atmospheric Composition And Structure: Cloud/Radiation Interaction
Scientific paper
Humic like substances (HULIS) are a class of compounds that are suspected to have an effect on cloud droplet activation properties of atmospheric aerosols because they decrease the surface tension of aqueous solutions quite efficiently. Surface active organic compounds have a tendency of concentrating on the surfaces of liquid droplets. If the total amount of surface active compound is small enough, partitioning of the substance on the surface depletes it from the droplet interior, decreasing the Raoult effect and increasing the Kelvin effect. Thus, the surface partitioning causes an increase of the critical supersaturation (Köhler curve maximum), and the effect gets stronger with decreasing size of the cloud condensation nucleus. In this study, the effects of HULIS on the activation of cloud droplets was studied by cloud parcel model calculations. Model results indicate that if the surface partitioning is not taken into account, the number of activated droplets can be highly overestimated. The simulations were made using particles containing 10-80% mass fraction of HULIS, while the remaining fraction of the particle was ammonium sulfate. The calculations indicated that the surface tension effects of humic-like compounds on the cloud activation become significant only when the weight fraction of the organics is very high. In contrast, if the surface partitioning is not taken into account, already a small weight fraction of organics will lead to significant increase in number of cloud droplets.
Kokkola Harri
Laaksonen Ari
Peräniemi A.
Raatikainen Tomi
Sorjamaa R.
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