Gschwend%20thesis.pdf

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(September 2-4, 1978). Also shown are the concentrations calculated from
the levels found in rain and Oyster Pond samples assuming that these were
at equilibrium with the atmosphere (physical data in Appendix iV). The
general range of these calculated values agrees well with the levels measured.
Seawater, at equilibrium with the air values found, would contain 0.4 to
6.6 ng o-xylene/kg. Seawater samples always contained
greater levels
of o-xylene than this, and therefore the atmosphere appears to have been a
sink, rather than a source, for C2- and C3-benzenes at this time.
Aromatic hydrocarbons introduced into the atmosphere are degraded
largely by reaction with OH- (Darnall et al., 1976). Reaction rates indicate
that this removal process from polluted air occurs with a half life of only
a few hours in daylight even for the slowest reacting alkylated benzene,
If the metropolitan area of New York were the source of a large plume of
aromatic hydrocarbon-rich air, by the time it reached Cape Cod, (ca. 8
hours, Cleveland et al., 1976), it would have been largely diluted and
cleansed by DH radical reactions. The 5-10 ng o-xylene/l-air found in
urban areas (Grob and Grob, 1971; Altshuller et al., 1971; Bertsch et al.,
1974; Ciccioli et al., 1976) may be reduced to the D.I to 1.5 ng o-xylene/
I-air found in this study.
It is difficult to know the nature of the source of C2- and C3~benzenes
. in the winter since the. samples in this study were taken in the late spring
through early fall. Levels almost never fell below 5 ng o-xylene/kg, eVen
in the winter; hence possibly the atmosphere serves as a buffer and main-
tains this "background" leveL. This would require the atmosphere to contain
about 1. I ng o-xylene/l-air, possibly a reasonabl e level for the metropolitan
Northeast U.S. In the sumer, it seems that the atmosphere is not a source,