engleski

Aerosol water soluble organic matter: Characterization of surface active substances by electrochemical method

The composition of the organic part of the atmospheric aerosol and the respective source contributions are far less known than those of the inorganic part. Significant proportion (30-80%) of the organic carbon is water-soluble (WSOC) and made up of polymer-type substances of higher molecular weight. Surface active substances (SAS) are the most reactive part of organic matter in natural environmental systems which accumulate at the interfaces and are present in aerosols and atmospheric precipitations. They form the surface film at the rain drop/air interface in which persistent organic pollutants accumulate, making long distance transmission possible. Surface active organic constituents can influence the surface tension of nucleating cloud droplets and thereby modify the critical supersaturation necessary to activate aerosol particles. The electrochemical methods offer an elegant way of SAS qualitative and quantitative characterization based on the measuring of electrode double layer capacity changes at mercury electrode surface. The method is applicable for the analysis of SAS in different aquatic systems, both freshwater and marine, which is very convenient for comparative studies. Aerosol samples (PM 2.5) were daily collected at Middle Adriatic station influenced by marine, regional and continental air masses inputs as well as from urban (Zagreb, Croatia) and rural (Kpuszta, Hungary) areas during late springearly autumn period and SAS were analysed by the electrochemical method. The highest SAS concentrations, expressed in equivalents of Triton-X-100, ranging from 0.34-0.91μg m-3 (mean 0.55± 0.21μg m-3, n=10) were detected in urban samples. The surfactant activities of marine, regional and continental samples were in the narrow ranges from 0.14-0.31μg m-3( mean 0.25±0.06μg m-3, n=10), 0.18-0.42μg m-3 ( mean 0.27±0.07 μg m-3, n=18) and 0.07-0.28μg m-3 (mean 0.17±0.075 μg m-3, n=10), respectively. The SAS concentrations in K-puszta aerosol samples ranged from 0.13-0.46 μg m-3 ( mean 0.29±0.11 μg m-3, n=6). Investigation of isolated humic-like substances (HULIS) confirmed that HULIS material exhibit strong surface activity. On the basis of the normalized surface activity we recommend that the surface activity of non-urban samples can be modeled by C9 fatty acid. This work was funded by the bilateral Croatian –Hungarian research project “Complex investigation of organic aerosols in rural, urban and marine environment“ and by the grant from the Croatian Ministry of Science, Education and Sports project “Nature of organic matter, interaction with traces and surfaces in environment” (098-0982934-2717).

Aerosol ; water soluble organic matter ; surface active substances ; electrochemical method

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