THE ATMOSPHERIC BIOGEOCHEMISTRY OF SELENIUM.

摘要

Selenium concentration which one measures in the atmosphere can be influenced by the particulate collection characteristics of the filter employed. It appears that in urban areas perhaps 35 - 55% of atmospheric particulate selenium may pass through cellulose and membrane filters type filters routinely used. A fifteen month record of particulate and vapor phase selenium concentrations has been collected at a semi-urban area in Rhode Island. Mean particulate and vapor phase concentrations during this period were 1.7 and 0.11 ng Se/m('3). Approximately 6% of the selenium was found to be in the vapor phase.; Much lower concentrations of both particulate and vapor phase selenium found above the marine boundary layer suggest that the ocean may be an important source of naturally produced reduced selenium species.; In an effort to evaluate the strength of the marine biosphere flux of selenium into the atmosphere, approximately seven hundred weekly particulate samples from a seven island sampling network in the North Pacific have been analyzed for selenium. Concentrations were found to be more closely related to primary productivity of the surrounding waters rather than to factors such as transport of continental/anthropogenic materials into the atmosphere of open ocean regions. Observed selenium concentrations were combined with literature estimates of primary productivity in ocean surface waters to calculate an ocean to atmosphere flux of approximately 7 x 10('9) g Se/y. It is believed that evasion of naturally produced vapor phase selenium species from the ocean surface and subsequent gas-to-particle conversion may explain much of the anomalous enrichment of particulate selenium observed in the marine atmosphere.; To put this ocean to atmosphere flux estimate into perspective a global budget for atmospheric selenium has been constructed. Perhaps 14 -22 x 10('9) g Se are cycled through the atmosphere annually. Approximately 60% of this flux is natural in origin and both natural and anthropogenic emissions are predominantly vapor phase in nature. Natural fluxes are dominated by the marine biosphere while the combustion of coal accounts for slightly less than half of the total anthropogenic emissions. (Abstract shortened with permission of author.)