Atmospheric Aerosol Water-Soluble Organic Carbon Measurement:
A Theoretical Analysis
- Publication date
- Publisher
Abstract
The measurement of Water-Soluble
Organic Carbon (WSOC) in atmospheric aerosol is usually carried out
by sample collection on filters, extraction in ultrapure water, filtration,
and measurement of the total organic carbon. This paper investigates
the role of different conditions of sampling and extraction as well
as the range of solubilities of the organic compounds that contribute
to the WSOC. The sampling and extraction of WSOC can be described
by a single parameter, <i>P</i>, expressing the ratio of
water used per volume of air sampled on the analyzed filter. Two cases
are examined in order to bound the range of interactions of the various
organic aerosol components with each other. In the first we assume
that the organic species form an ideal solution in the particle and
in the second that the extraction of a single compound is independent
of the presence of the other organics. The ideal organic solution
model predicts that species with water solubility as low as 10<sup>–4</sup> g L<sup>–1</sup> contribute to the measured
WSOC. In the other end, the independent compounds model predicts that
low-solubility (as low as 10<sup>–7</sup> g L<sup>–1</sup>) compounds are part of the WSOC. Studies of the WSOC composition
are consistent with the predictions of the ideal organic solution
model. A value of <i>P</i> = 0.1 cm<sup>3</sup> m<sup>–3</sup> is proposed for the extraction of WSOC for typical organic aerosol
concentrations (1–10 μg m<sup>–3</sup>). WSOC
measurements under high concentration conditions often used during
source sampling will tend to give low WSOC values unless higher <i>P</i> values are used