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18.
Speciation of Organic Matter in Fog Droplets: How Far are We from
Mass Closure?
Pierre
Herckes, Taehyoung Lee, Hui Chang, Jacqueline Carrillo, Sarah
Youngster and Jeffrey L. Collett, Jr.
Colorado
State University, Department of Atmospheric Science, Fort Collins
CO 80523
Fog and cloudwater composition has been studied
for decades, the focus of research being mainly inorganic compounds,
specifically those relevant for sulfur oxidation and droplet acidity.
In recent years organic matter in fog and cloud droplets has begun
to receive more attention. Today, total organic carbon and certain
compound families are frequently quantified but most of the organic
matter remains unspeciated and poorly characterized.
In winter of 2003/2004 a fogwater study was conducted
in Fresno (CA). One of the goals was a better characterization
of the fog organic matter. We used different techniques to characterize
the organic matter as a whole (TOC, DOC, DON) and to fractionate
it according to polarity (e.g. anion exchange chromatography)
or molecular size (ultrafiltration). We also performed individual
species quantification by techniques like ion chromatography (IC),
high performance liquid chromatography (HPLC) and gas chromatography
coupled to mass spectrometry (GC/MS) after liquid/liquid extraction.
We will present results of these studies and discuss
our current understanding of the organic matter in fog droplets.
The results reveal that we can account for most of the low molecular
weight organic matter with the dominant species being small carboxylic
acids and aldehydes. The significance of high molecular weight
compounds will be discussed and compared to previous studies.
Speciation at a molecular level of these compounds is unlikely.
Molecular markers are also detected in the soluble and insoluble
fractions of the organic matter, but their contributions to the
total organic carbon are insignificant.
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