Diurnal Variability of Persistent Organic Pollutants in the Atmosphere over the Remote Southern Atlantic Ocean
Résumé
A diel (24-h) cycle with daytime atmospheric concentrations higher than
nighttime concentrations by a factor of 1.5–3 was observed for several low molecular
weight polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) in
remote areas of the tropical South Atlantic during a cruise in October–November 2005. In
contrast, high molecular weight PCBs and PAHs did not display diurnal variability. A
model which has successfully explained diel variability of persistent organic pollutants (POPs)
over land could not reproduce the observed diel cycle by considering variability in
temperature, atmospheric OH radical concentrations, atmospheric boundary layer height
and wind speed as causal factors. We used the model to conduct two bounding scenarios to
explore the possibility that phytoplankton biomass turn-over in the surface ocean drives the
observed variability in air concentrations. The model could only qualitatively reproduce the
field observations of diel variability for low chlorinated PCB congeners when the ocean
acts as a source of pollutants to the atmosphere, and when variability in biomass drives
variability in the capacity of the surface ocean.