114
Pesticides, Organic Contaminants, and Pathogens in Air
in different fog events which had no obvious explanation. The liquid water
content, which ranged from 0.024 to 0.080 g/m 3 , total organic carbon content
(38–55 mg/L), and pH (5.4–7) did not vary that much between samples and
did not show correlational trends. Temperature effects were hypothesized
to have played a small role. H generally increases with increasing temperature, and most of the calculated H constants were from data at 20°C or 25°C.
Since the fog collections were made in atmospheres of 1.5°C–8.5°C, measured
distributions (D) should be lower than those calculated from H, but only by
factors of 2–4.
Seiber et al. (1993) found enrichment factors of only 5.7 (chlorpyrifos), 3.3
(diazinon), 2.7 (parathion), and 0.01 (methidathion). These magnitudes were
considerably less than those of Glotfelty et al. (1986, 1987) and almost within
the range predicted for temperature effects on distribution. Seiber et al. (1993)
suggested the operation of variables, or sources of error, not yet considered
or explained. It should be noted that Seiber et al. (1993) used a Tefon strand
collector while the Glotfelty et al. (1986, 1987) collections were made with the
rotating stainless steel screen device (Glotfelty et al., 1986).
Two primary hypotheses have emerged to explain the enrichment of
organics in the aqueous phase of fogwater. (1) Organic solutes or nonflterable colloids in the water phase enhance water solubility above that in pure
water, or sorb organics so that more are bound in the fogwater phase than in
pure water. (2) The air–water interface acts as a third phase, or compartment,
in what had been assumed to be a simple 2-phase, or 2-compartment (viz. air
and water) process. Capel et al. (1990) provided arguments in favor of the frst
hypothesis, essentially supporting the conclusions of Glotfelty et al. (1986,
1987). They argued that, on a mass basis, the “dissolved” organic fraction in
fogwater is 10–100 times typical values reported for rain, lakes, and rivers.
They also showed that the surface tension of fog is less than that of pure
water, refecting the presence of surface-active material. They assumed, then,
that a portion of the fog droplet/air interface is covered with organic chemicals so that airborne chemicals confront an organic/air interface rather than
a water/air interface. This would provide a mechanism for the concentration
or enrichment of hydrophobic organic contaminants in the fog droplet.
Sagebiel and Seiber (1993) provided new evidence for the involvement of
an interface in the enrichment process. They measured the air–water distribution of a number of phenolic products of incomplete combustion of wood
in fogs collected in a winter-time residential setting in the Central Valley of
California. The three most signifcant phenols, guaiacol, 4-methylguaiacol,
and syringol, showed little to no enrichment. In plotting enrichment factor
vs either octanol–water partition coeffcient (Figure 7.6a) or water solubility
(Figure 7.6b), it was clear that these wood smoke marker chemicals extended
the range of solubilities represented by the pesticides studied by Glotfelty
et al. (1987) to much higher water solubility (Figure 7.6b) or much lower
octanol–water partition coeffcient (Figure 7.6a), demonstrating that enrichment was limited to nonpolar organics in a regular fashion. This argued for a
Pesticides, Organic Contaminants, and Pathogens in Air
in different fog events which had no obvious explanation. The liquid water
content, which ranged from 0.024 to 0.080 g/m 3 , total organic carbon content
(38–55 mg/L), and pH (5.4–7) did not vary that much between samples and
did not show correlational trends. Temperature effects were hypothesized
to have played a small role. H generally increases with increasing temperature, and most of the calculated H constants were from data at 20°C or 25°C.
Since the fog collections were made in atmospheres of 1.5°C–8.5°C, measured
distributions (D) should be lower than those calculated from H, but only by
factors of 2–4.
Seiber et al. (1993) found enrichment factors of only 5.7 (chlorpyrifos), 3.3
(diazinon), 2.7 (parathion), and 0.01 (methidathion). These magnitudes were
considerably less than those of Glotfelty et al. (1986, 1987) and almost within
the range predicted for temperature effects on distribution. Seiber et al. (1993)
suggested the operation of variables, or sources of error, not yet considered
or explained. It should be noted that Seiber et al. (1993) used a Tefon strand
collector while the Glotfelty et al. (1986, 1987) collections were made with the
rotating stainless steel screen device (Glotfelty et al., 1986).
Two primary hypotheses have emerged to explain the enrichment of
organics in the aqueous phase of fogwater. (1) Organic solutes or nonflterable colloids in the water phase enhance water solubility above that in pure
water, or sorb organics so that more are bound in the fogwater phase than in
pure water. (2) The air–water interface acts as a third phase, or compartment,
in what had been assumed to be a simple 2-phase, or 2-compartment (viz. air
and water) process. Capel et al. (1990) provided arguments in favor of the frst
hypothesis, essentially supporting the conclusions of Glotfelty et al. (1986,
1987). They argued that, on a mass basis, the “dissolved” organic fraction in
fogwater is 10–100 times typical values reported for rain, lakes, and rivers.
They also showed that the surface tension of fog is less than that of pure
water, refecting the presence of surface-active material. They assumed, then,
that a portion of the fog droplet/air interface is covered with organic chemicals so that airborne chemicals confront an organic/air interface rather than
a water/air interface. This would provide a mechanism for the concentration
or enrichment of hydrophobic organic contaminants in the fog droplet.
Sagebiel and Seiber (1993) provided new evidence for the involvement of
an interface in the enrichment process. They measured the air–water distribution of a number of phenolic products of incomplete combustion of wood
in fogs collected in a winter-time residential setting in the Central Valley of
California. The three most signifcant phenols, guaiacol, 4-methylguaiacol,
and syringol, showed little to no enrichment. In plotting enrichment factor
vs either octanol–water partition coeffcient (Figure 7.6a) or water solubility
(Figure 7.6b), it was clear that these wood smoke marker chemicals extended
the range of solubilities represented by the pesticides studied by Glotfelty
et al. (1987) to much higher water solubility (Figure 7.6b) or much lower
octanol–water partition coeffcient (Figure 7.6a), demonstrating that enrichment was limited to nonpolar organics in a regular fashion. This argued for a