In situ and denuder-based measurements of elemental and reactive gaseous mercury with analysis by laser-induced fluorescence – results from the Reno Atmospheric Mercury Intercomparison Experiment

摘要

The University of Miami (UM) deployed a sequential two-photon laser-inducedfluorescence (2P-LIF) instrument for the in situ measurement of gaseouselemental mercury, Hg(0), during the Reno Atmospheric Mercury IntercomparisonExperiment (RAMIX) campaign. A number of extended sampling experiments,typically lasting 6–8 h but on one occasion extending to ∼ 24 h,were conducted, allowing the 2P-LIF measurements of Hg(0) concentrations to becompared with two independently operated instruments using gold amalgamationsampling coupled with cold vapor atomic fluorescence spectroscopic (CVAFS)analysis. At the highest temporal resolution, ∼ 5 min samples, thethree instruments measured concentrations that agreed to within 10–25 %.Measurements of total mercury (TM) were made by using pyrolysis to converttotal oxidized mercury (TOM) to Hg(0). TOM was then obtained by difference.Variability in the ambient Hg(0) concentration limited our sensitivity formeasurement of ambient TOM using this approach. In addition, manually sampledKCl-coated annular denuders were deployed and analyzed using thermaldissociation coupled with single-photon LIF detection of Hg(0). The TOMmeasurements obtained were normally consistent with KCl denuder measurementsobtained with two Tekran speciation systems and with the manual KCl denudermeasurements but with very large uncertainty. They were typically lower thanmeasurements reported by the University of Washington (UW) Detector forOxidized Hg Species (DOHGS) system. The ability of the 2P-LIF pyrolysissystem to measure TM was demonstrated during one of the manifold HgBrspikes but the results did not agree well with those reported by the DOHGSsystem. The limitations of the RAMIX experiment and potential improvementsthat should be implemented in any future mercury instrument intercomparisonare discussed. We suggest that instrumental artifacts make a substantialcontribution to the discrepancies in the reported measurements over thecourse of the RAMIX campaign. This suggests that caution should be used indrawing significant implications for the atmospheric cycling of mercury fromthe RAMIX results.