Global evaluation and calibration of a passive air sampler for gaseous mercury

Abstract

Abstract. Passive air samplers (PASs) for gaseous mercury (Hg) were deployed for time periods between 1 month and 1 year at 20 sites across the globe with continuous atmospheric Hg monitoring using active Tekran instruments. The purpose was to evaluate the accuracy of the PAS vis-à-vis the industry standard active instruments and to determine a sampling rate (SR; the volume of air stripped of gaseous Hg per unit of time) that is applicable across a broad variety of 5 conditions. The sites spanned a wide range of latitudes, altitudes, meteorological conditions, and gaseous Hg concentrations. Precision, based on 378 replicated deployments performed by numerous personnel at multiple sites, is 3.6 ± 3.0 % * , confirming the PAS's excellent reproducibility and ease-of-use. Using a SR previously determined at a single site, gaseous Hg concentrations derived from the globally distributed PASs deviate from Tekran-based 10 concentrations by 14.2 ± 10 %. A recalibration using the entire new data set yields a slightly higher SR of 0.1354 ± 0.016 m 3 day -1 . When concentrations are derived from the PAS using this revised SR the difference is reduced to 8.8 ± 7.5 %. At the mean gaseous Hg concentration across the study sites of 1.54 ng m -3 , this represents an ability to resolve concentrations to within 0.13 ng . m -3 . Adjusting the sampling rate to deployment specific temperatures and wind speeds does 15 not decrease the difference in active-passive concentration further (8.7 ± 5.7 %), but reduces its variability by leading to better agreement in Hg concentrations measured at sites with very high and very low temperatures and very high wind speeds. This value (8.7 ± 5.7 %) represents a conservative assessment of the overall uncertainty of the PAS due to inherent uncertainties of the Tekran instruments. Going forward, the recalibrated SR adjusted for temperature and wind speed 20 should be used, especially if conditions are highly variable or deviate considerably from the average of the deployments in this study (9.89 °C, 3.41 m s -1 ). Overall, the study demonstrates that the sampler is capable of recording background gaseous Hg concentrations across a wide range of environmental conditions with accuracy similar to that of industry standard active sampling instruments. Results at sites with active speciation units were inconclusive on whether the PASs 25 take up total gaseous Hg or solely gaseous elemental Hg primarily because gaseous oxidized Hg concentrations were in a similar range as the uncertainty of the PAS.* subscripted numbers are not significant, but are reported to reduce rounding errors in subsequent studies (see Section 2.3 for details) Atmos. Chem. Phys. Discuss., https://doi

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

“…Two trapping methods have been previously used to collect nanogram quantities of GEM for isotopic analysis: (i) amalgamation of GEM on gold coated quartz beads, ,,, and (ii) activated carbon traps impregnated with halogens (Cl, I) ,,,, or sulfur. , A third method that is commonly used to trap GEM, not during ambient GEM sampling, but as part of laboratory preconcentration methods, consists of purging GEM through a strongly oxidizing, acidic aqueous solution. , There are important differences between direct manual sampling of GEM onto gold or activated carbon, and the ISO-GEM application: 1. Direct sampling is done in air at 1–2 L min –1 flow rates, while 2537X cell vent trapping is done in low flow (80 mL/min) high purity, dry argon.…”