| Abstract
| - Water-soluble organic compounds (WSOC) often representa large fraction of the total organic mass found in theatmospheric aerosol. They play a very important role indetermining the ability of aerosol particles to act as cloudcondensation nuclei (CCN), influencing cloud and fogformation and cloud albedo. Molecular characterization ofWSOC in fogwater samples was achieved using a two-stage ion-trap mass spectrometer equipped with electrosprayionization (ESIMS/MS). Negative ionization conditions inthe electrospray interface finalized our characterization ofthe acidic fraction of WSOC that comprises both mono-and di-carboxylic acids and polycarboxylic acids for whicha similarity was suggested with naturally occurringhumic (or fulvic) acids, and which are sometimes referredto in the literature as humic-like substances (HULIS).Molecular structure elucidation was accomplished usingseveral model compounds and exploiting mass spectralresolution for compound separation. Single compoundidentification was attempted by recording typical MS/MSfragmentation pathways of model substances and comparingthem with actual sample pathways in order to establishspecific correspondences. Besides this spectrum-matchingidentification process, MS/MS interpretation led toseveral hypothetical structures for HULIS, extending thecomprehension of their chemical nature. Suwannee Riverfulvic acid, proposed as a suitable model for representingthe complex mixtures of HULIS in cloud and water aerosolextracts, was also analyzed, and the data obtained werecompared with those from WSOC.
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