Assessing the contribution of natural sources to regional atmospheric mercury budgets

Naturally mercury-enriched substrate is a long-lived source of mercury to t he global atmospheric mercury cycle. Field flux chambers, laboratory gas ex change chambers and micrometeorological methods may be applied to estimate emissions from these sources. However, field chamber experimental design ma y affect the magnitude of the fluxes measured, and the laboratory chamber o nly provides a minimum estimate of flux. Many factors, such as mercury conc entration and speciation in substrate, light, precipitation, and temperatur e, influence the emission of mercury from the substrate. Mercury concentrat ion in the substrate is a dominant factor controlling emissions and may be used to predict emissions from regions of mercury enrichment. Mercury fluxe s measured from three areas of natural enrichment and three areas with low levels of mercury enrichment are 1-5 orders of magnitude greater than the v alue applied to global belts of natural enrichment. Preliminary scaling of emissions from one of these areas and for western North America indicates t hat mercury enriched areas may be significant sources of mercury to the atm osphere, and that their contribution to regional and global atmospheric bud gets needs to be reassessed. (C) 2000 Elsevier Science B.V. All rights rese rved.