Automated Stable Isotope Sampling of Gaseous Elemental Mercury (ISO-GEM): Insights into GEM Emissions from Building Surfaces

Atmospheric monitoring networks quantify gaseous elemental mercury (GEM) concentrations, but not isotopic compositions. Here, we present a new method for automated and quantitative stable isotope sampling of GEM (ISO-GEM) at the outlet of a commercial Hg analyzer. A programmable multivalve manifold selects Hg at the analyzer inlet and outlet based on specific criteria (location, time, GEM concentration, auxiliary threshold). Outlet Hg recovery was tested for gold traps, oxidizing acidic solution traps, and activated carbon traps. We illustrate the ISO-GEM method in an exploratory study on the effect of building walls on local GEM. We find that GEM concentrations directly at the building surface (wall inlet) are significantly enhanced (mean 3.8 +/- 1.8 ng/m(3)) compared to 3 m from the building wall (free inlet) (mean 1.5 +/- 0.4 ng/m(3)). GEM delta Hg-202 (-1.26 parts per thousand +/- 0.41 parts per thousand, 1 SD, n = 16) and Delta Hg-199 (-0.05 parts per thousand +/- 0.10 parts per thousand, 1 SD, n = 16) at the wall inlet were different from ambient GEM delta Hg-202 (0.76 parts per thousand +/- 0.09 parts per thousand, 1 SD, n = 16) and Delta Hg-199 (-0.21 parts per thousand +/- 0.05 parts per thousand, 1 SD, n = 16) at the free inlet. The isotopic fingerprint of GEM at the wall inlet suggests that GEM emission from the aluminum building surface affected local GEM concentration measurements. These results illustrate the versatility of the automated Hg isotope sampling.