Atmospheric gaseous elemental mercury isotopic compositions in the Tibetan Plateau and surroundings

Isotope ratios of Hg in trapping solutions were measured using cold vapor-multicollector inductively coupled plasma mass spectrometry (CV-MC-ICPMS, Nu Instruments, U.K.). Mass dependent fractionation signatures (δ199Hg, δ200Hg, δ201Hg, δ202Hg, δ204Hg, in ‰) were calculated as follows:δxxxHg = [(xxxHg/198Hg)sample/(xxxHg/198Hg)Nist 3133 - 1]×1000‰   (1)where xxxHg represents the mercury stable isotopes (199Hg, 200Hg, 201Hg, 202Hg, and 204Hg).

NIST 3133 refers to bracketing NIST (National Institute of Standards & Technology) SRM (Standard Reference Material) 3133 mercury standard solution, of which the mercury isotope ratios were measured before and after the sample collection to correct the mass bias of MC-ICPMS. MIF signatures (Δ199Hg, Δ200Hg, Δ201Hg, and Δ204Hg, in ‰) were calculated based on the Kinetic MDF law as follows:ΔxxxHg (‰) = δxxxHg – βxxx × δ202Hg  (2)where βxxx is 0.252, 0.5024, 0.752, and 1.493 for 199Hg, 200Hg, 201Hg, and 204Hg, respectively. The final analytical uncertainty (2sd) of each GEM sample reported here is the larger 2sd value of either the sample replicates or the repeated measurements of NIST SRM 8610 during the whole analytical sessions.