Particulate selenium in the atmosphere

It is estimated that one-half to two-thirds of the worldwide selenium emissions come from natural sources. Two-thirds of the anthropogenic selenium emissions come from combustion: 50% from coal, 9% from oil and 10% from other combustion. Selenium is a key tracer for sulfate aerosols. The largest source of data on atmospheric selenium and sulfur at remote sites is the Interagency Monitoring of Protected Visual Environments (IMPROVE) network with 76 remote aerosol sampling sites across the USA. The chapter discusses the network and the results obtained. Mean fine particle selenium concentrations range from 0.05 ng/m3 in the West during winter to 1 ng/m3 in the Appalachian Mountains. Selenium from the marine biosphere is significant at sites with major marine influences but contributes little at most continental sites. Nearly all particulate selenium appears to be associated with sulphur, especially in the East. Data indicate that selenium observed at remote sites is from regional rather than local sources, especially in summer. 14 refs., 9 figs., 1 tab