Assessing the contribution of natural sources to the global mercury cycle:The importance of intercomparing dynamic flux measurements

In order to constrain the contribution of natural sources of mercury to the global atmospheric cycle we need to: 1. assess the methods used to measure mercury flux, 2. characterize those factors most important in controlling emissions, 3. develop a database of emissions from representative locations , and 4. develop a means of scaling up measured emissions to estimate fluxe s on a regional basis. This paper describes how an international multi-coll aborator project, the Nevada SToRMS Project, held September 1997 in Reno, N evada, USA, contributed to our ability to constrain natural source mercury emissions. This study entailed a field intercomparison of those methods typ ically applied to measure mercury flux from substrate combined with evening workshops and roundtable discussions. The project was unique in that it fo cused on assessing our ability to measure the flux of an environmental cont aminant. This is more difficult than measurement of the concentration of a contaminant because of the number and nature of the variables which influen ce the field flux measurements, including experimental design, spatial hete rogeneity, and temporally changing environmental conditions. As a result of the Nevada SToRMS Project, rapid and significant advances in our understan ding of how to constrain emission fluxes from large areas of mercury enrich ment were realized. Because this intercomparison was a multi-investigator p roject, the results and implications of the project have been broadly circu lated. The sincere scientific collaboration that evolved amongst those work ing on the study has led to significant advancements in our understanding o f the fate and transport of mercury in the environment.