A new approach for the fractionation of water-soluble organic carbon in atmospheric aerosols and cloud drops |
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| Institution: | 1. Metropolitan Water District of Southern California, Water Quality, La Verne, CA 91750, USA;2. National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA;3. Center for Health Effects of Environmental Contamination (CHEEC), University of Iowa, Coralville, IA 52242, USA;4. Medical Research Solutions, LLC, Montgomery Village, MD 20886, USA;5. College of Engineering, Computing and Applied Sciences, Clemson University, Clemson, SC 29631, USA;1. Department of Environmental Science and Engineering, Beijing Technology and Business University, Beijing 100048, PR China;2. Department of Civil and Environmental Engineering, The George Washington University, Washington, DC 20052, USA;3. State Key Joint Laboratory of Environmental Simulation and Pollution Control, State Environmental Protection Key Laboratory of Microorganism Application and Risk Control (MARC), School of Environment, Tsinghua University, Beijing 100084, PR China |
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| Abstract: | A novel approach is described for the fractionation of water-soluble organic carbon (WSOC) in atmospheric aerosols and cloud drops. The method is based on the preliminary adsorption of the sample, acidified at pH 2, on a polymeric styrene-divinylbenzene resin (XAD-2) and subsequent elution with a series of solvents, which leads to the fractionation of the sample into three classes of compounds. The method was set up using synthetic mixtures of organic compounds and then applied to selected samples of atmospheric aerosols and cloud drops. All samples and collected fractions were analysed using size exclusion chromatography (SEC). This method proved particularly useful both in providing information on the organic content of the samples and for the characterisation of the macromolecular compounds (MMCs) in the samples. Synthetic samples were prepared using humic, fulvic and tannic acid to simulate naturally occurring MMCs. In the first fraction, eluted with HCl, only the most soluble organic compounds (oxalic acid, formic acid and acetic acid) were collected. In the second fraction, eluted with methanol, the major part of the organic material was collected together with the more hydrophilic constituents of the humic substances. In the third fraction, it was possible to separately recover the more hydrophobic component of the humic substances. A large number of atmospheric samples (fog, aerosol, cloud) were then analysed using SEC. Most of these samples evidenced a noteworthy chromatogram at 254 nm. Moreover, the chromatographic area evidenced a clear linear correlation with the total organic carbon (TOC) values. The fractionation method on XAD-2 was finally applied to selected atmospheric samples, yielding three classes of organic compounds. In each sample, a non-negligible amount of compounds with dimensional and chemical properties similar to humic substances were collected in the third fraction. The carbon content in this latter fraction was estimated both by TOC and by means of the correlation between TOC and SEC area. |
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