Continued Field Comparison Of MDN Mercury Wet Deposition Collectors: MDN Aerochem and MDN NCONN-ADS

Robert Brunette
Frontier Geosciences Inc,
Seattle, WA USA

On October 24, 2006 the NADP voted and approved the use of a second MDN wet deposition collector (MDN NCONN-ADS) in an effort to modernize and eventually replace the aging original MDN collector design (MDN Aerochem). The MDN Aerochem (MDN ACM) is still deployed at a majority of the MDN sites and continues to support the MDN well. The new MDN NCONN-ADS has replaced several aging MDN ACM collectors and essentially has been deployed at all new MDN sites started since January 2007. The MDN NCONN-ADS collector utilizes an optical sensor versus the MDN ACM 11 grid sensor and has several features that greatly improve the operational efficiency of wet deposition mercury collection.

Although the MDN NCONN-ADS collector, prior to approval, was well tested and compared to the MDN Aerochem, it was encouraged to continue co-located collector measurements in order to monitor any potential differences in capture efficiency and chemistry for mercury. Three sites have continued these co-located MDN collector measurements: (1) Seattle, Washington State (MDN WA18) operated by Frontier Geosciences Inc (collector comparison ~ 3 years) (2) Kejimkujik National Park, Nova Scotia, Canada operated by Environment Canada (collector comparison ~ 1 year) and (3) Underhill, Vermont (MDN VT99) operated by Ecosystems Research Group, Ltd (collector comparison ~ 3 years). Capture efficiency, total mercury in precipitation and total mercury wet deposition at all three of these geographically diverse sites are presented.