Evaluation of an Improved Reactive Mercury Active System: Uncertainties and Applicability in Polluted Environments

Reactive mercury (RM) has a short atmospheric residence time of hours to weeks, leading to primarily local deposition. Gaseous elemental mercury (GEM) has a residence time of 0.3-1 year, resulting in long-range transport. The Reactive Mercury Active System (RMAS) developed by the University of Nevada, Reno (UNR) is a membrane-based Hg-monitoring system. This study presents the first independent evaluation of RMAS outside the UNR group, focusing on its performance in polluted environments. The impacts of key factors on the accuracy of RMAS and the deconvolution method for thermal desorption profiles were evaluated. Nylon membranes exhibit variable capture efficiencies (12-81%) of RM across compounds. Consequently, corrections based on multiple linear regression were utilized to enhance RM compound identification. In polluted environments with high fine particulate matter (PM2.5) concentrations (annual average concentration >10 μg m-3), the sampling flow rate did not affect the RM concentration but could alter its chemistry via ion exchange. Uncertainties were estimated to be ±19% for the overall concentration and ±6-47% for dominant RM forms. This work showed that RMAS is a promising tool for speciated RM monitoring, supporting the effectiveness evaluation of the Minamata Convention.