Reactive mercury (RM) is an important component of the global atmospheric mercury cycle, but measurement currently depends on un-calibrated, operationally defined methods with large uncertainty and demonstrated interferences and artifacts. Cation exchange membranes (CEM) provide a promising alternative methodology for quantification of RM, but method validation and improvement are ongoing. For the CEM material to be reliable, uptake of gaseous elemental mercury (GEM) must be negligible for all conditions, and RM compounds must be captured and retained with high efficiency. In this study the performance of CEM material under exposure to high concentrations of GEM (1.43 × 10 6 –1.85 × 10 6 pg m −3 ) and reactive gaseous mercury bromide (HgBr 2 ~ 5000 pg m −3 ) was explored, using a custom-built mercury vapor permeation system, with quantification of total permeated Hg accomplished via pyrolysis at 600 °C and detection using a Tekran ® 2537A. Permeation tests were conducted for 24 to 72 hours in clean laboratory air, with absolute humidity levels ranging from 0.1–10 g m −3 water vapor. Gaseous elemental mercury uptake by the CEM material averaged no more than 0.004 % of total exposure for all test conditions, which equates to a non-detectable GEM artifact for typical ambient air sample concentrations. Recovery of HgBr 2 on CEM filters was > 100 % compared to calculated total permeated HgBr 2 , suggesting incomplete thermal decomposition at the pyrolyzer, as the CEM material collected HgBr 2 with less than 1 % downstream breakthrough on average, implying a high collection efficiency.