Atmospheric Concentrations and Deposition of Trichloroacetic Acid in Scotland: Results from a 2-Year Sampling Campaign
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Date
2003Author
Heal, Mathew R
Reeves, Nicholas M
Cape, Neil
Metadata
Abstract
The first long-term concurrent measurements of trichloroacetic
acid (TCA) in rainwater, in cloudwater, and in air
(both gas and particle phase) are reported. Measurements
were made weekly between June 1998 and April 2000 at
a rural forested upland site in SE Scotland. Rainwater TCA
concentration did not differ significantly between two
elevations (602 and 275 m asl), with precipitation-weighted
mean values of 0.77 and 0.70 mu g L-1, respectively ( n>
75). The precipitation-weighted mean concentration of TCA
in cloudwater at the highest elevation was 0.92 mu g L-1,
yielding an average cloudwater enrichment factor of 1.2,
considerably lower than for other inorganic ions measured.
Rainwater and cloudwater TCA concentrations did not
vary systematically with season. Since wet precipitation
depth also did not vary systematically with season, the wet
deposition fluxes of TCA were likewise invariant (annual
fluxes at the highest elevation of 880 and 130 mu g m-2,
respectively, for rain and cloud interception to spruce
forest). Weekly integrated concentrations of TCA in air (gas
and particle) were very low (median 25 pgm-3, range<LOD-
110 pg m-3). The estimated upper limit for annual dry
deposition of TCA at this site was 20 mu g m-2, assuming
a deposition velocity of 2 cm s-1. Concentrations of
TCA in air correlated reasonably strongly with concentrations
in rainwater, with a partition ratio approximately equal
to the Henry’s law coefficient. On average, only about 23%
of TCA measured in Edinburgh air was associated with
the particle phase. These measurements are consistent with
the observed high scavenging ratio of TCA (ratio of
concentration in air to concentration in rainwater). Overall,
these data confirm that the atmosphere is an important
source of TCA to the environment and that precipitation is
the dominant transfer mechanism. In line with previous
work, the atmospheric deposition flux is greater than expected
from the current understanding of atmospheric production
of TCA from anthropogenic precursors. It is suggested
that aqueous-phase processes could lead to greater atmospheric conversion of chlorinated solvent precursors
to TCA than is currently accepted.