Dissolved and gas-phase concentrations of nine polycyclic
aromatic hydrocarbons and 46 polychlorinated biphenyl
congeners were measured at eight sites on the Chesapeake
Bay at four different times of the year to estimate net
diffusive air−water gas exchange rates. Gaseous
PAHs
are absorbed into the bay's surface waters during the
spring, and lighter compounds revolatilize in the late
summer
and early fall due to seasonal changes in surface water
temperature and atmospheric PAH levels. On an annual
basis, the atmosphere is a net source of volatile PAHs
to the Chesapeake Bay, and gas absorption may be the
largest external source of fluorene and phenanthrene,
providing up to three times the combined loadings from
wet and dry aerosol deposition and from tributaries.
Largest
PAH absorptive fluxes occurred in the northern Chesapeake
when prevailing winds carried PAH-enriched air from the
Baltimore-Washington urban area over the bay. In
contrast to PAHs, PCBs volatilize from the Chesapeake Bay
throughout the year, with the largest fluxes occurring
in September and the smallest fluxes in June.
However,
higher chlorinated (
−
) homologues
are absorbed by
bay waters during most of the year. Highest PCB
volatilization
rates were observed in the northern Chesapeake Bay
and near the James River in the southern bay, indicating
volatilization offsets PCB loading from the bay's
tributaries.
Volatilization is the dominant removal process for PCBs
from
the Chesapeake Bay, removing an estimated 400 kg/year. This value is larger than current external PCB
loadings,
suggesting that release of PCBs from historically
contaminated sediments supports volatilization from the
bay.
Concentrations of polycyclic aromatic hydrocarbons
(PAHs) were measured in the coastal New Jersey atmosphere
as part of the New Jersey Atmospheric Deposition
Network (NJADN). PAH results from the first year of
atmospheric sampling (Oct 1997−Oct 1998) at a suburban
site near New Brunswick, NJ and a coastal site at
Sandy Hook, NJ are presented. PAHs (36) were analyzed
at both sites including phenanthrene and benzo[a]pyrene
whose concentrations ranged from 0.74 to 20.9 ng/m3
and 0.0020 to 0.62 ng/m3, respectively. PAH concentrations
at the suburban site were 2× higher than concentrations
measured at the coastal site, consistent with the closer
proximity of NB to urban/industrial regions than SH. The
seasonal trends of particulate PAH concentrations indicate
that PAH sources such as fuel consumption for domestic
heating and vehicular traffic drive their seasonal occur
rence. While gaseous concentrations of methylated
phenanthrenes and pyrene were higher during the winter
and similar to high molecular weight PAHs, phenanthrene
and fluoranthene show the opposite seasonal trend with
concentrations peaking in the summer months. Because
temperature accounted for less than 25% of the variability
in atmospheric concentrations, seasonal variability could
not be attributed to temperature-controlled air-surface
exchange. PAH concentrations in the New Jersey coastal
atmosphere indicate the importance of local and regional
sources originating from urban/industrial areas to the N, NE,
and to the SW.
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