Low Molecular Weight Organic Compounds in the Po Valley Fog Water
Organic compounds which play a role in the chemistry of the atmospheric dispersed liquid phase (fog, cloud, precipitation) must be of sufficiently high polarity and low molecular weight to render them soluble: i.e. carbonylic and carboxylic compounds with less than three carbon numbers. Carbonyls can interact with S(IV) species in solution to form hydroxyalkanesulfonic acids, adducts which effectively increase the solubilities of both carbonyl and S(IV) species and so constitute an important aqueous phase reservoir. Organic acids can contribute significantly to the acidity of fog and cloud droplets in the absence of H3O+ provided by strong, inorganic acids. Identification and quantitication of species within these two classes of compounds were performed on fog water samples collected at a field station in the Po Valley. Several carbonyl compounds were detected, though formaldehyde was by far the most abundant species present, with measured comcentrations up to 567 µmol/1. The percentage of formaldehyde bound as hydroxymethanesulfonic acid (HMSA) ranged from 35% to 99%. Acetaldehyde was present at concentrations of about one order of magnitude less than formaldehyde. Traces of acrolein were also present in these fog samples. The average concentrations of formic and acetic acid for all samples were 127 µmol/1 and 104 µmol/1 respectively, but traces of propionic acid were also present.
KeywordsCarbonyl Compound Cloud Droplet Total Ionic Strength Carboxylic Compound Phase Distribution Equilibrium
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