Tropospheric GOM at the Pic du Midi Observatory—Correcting Bias in Denuder Based Observations

Gaseous elemental mercury (GEM, Hg) emissions are transformed to divalent reactive Hg (RM) forms throughout the troposphere and stratosphere. RM is often operationally quantified as the sum of particle bound Hg (PBM) and gaseous oxidized Hg (GOM). The measurement of GOM and PBM is challenging and under mounting criticism. Here we intercompare six months of automated GOM and PBM measurements using a Tekran (TK) KCl-coated denuder and quartz regenerable particulate filter method (GOMTK, PBMTK, and RMTK) with RMCEM collected on cation exchange membranes (CEMs) at the high altitude Pic du Midi Observatory. We find that RMTK is systematically lower by a factor of 1.3 than RMCEM. We observe a significant relationship between GOMTK (but not PBMTK) and Tekran flushTK blanks suggesting significant loss (36%) of labile GOMTK from the denuder or inlet. Adding the flushTK blank to RMTK results in good agreement with RMCEM (slope = 1.01, r2 = 0.90) suggesting we can correct bias in RMTK and GOMTK. We provide a bias co...