In situ high temporal resolution analysis of elemental mercury in natural waters

Volatilization of elemental Hg represents an important Hg flux for many aquatic systems. In order to model this flux accurately, it is necessary to measure elemental Hg concentrations in air and water, as well as meteorological variables. Up to now, temporal resolution of elemental Hg analysis has been low (0.5–1 h between data points) compared to other variables used in models (5 min between data points). Here we present an analytical system that allows for the near-real time measurement (every 5 min) of dissolved gaseous mercury (DGM). This system is automated and has a detection limit of 8.5 pg l−1. By using solar radiation as a predictor of DGM concentrations in aquatic systems, we demonstrate the fast response time of the analytical system to fluctuations in ambient DGM in the St. Lawrence river, at sunrise. Complete covering of the purge apparatus and tubing resulted in a 2.6-fold decrease in the slope of the DGM versus light relationship, revealing the importance of light shielding the instrumentation to obtain realistic values.