Abstract
Abstract. Passive air sampling of gaseous mercury (Hg) requires a high level of accuracy to discriminate small differences in atmospheric concentrations. Meteorological parameters have the potential to decrease this accuracy by impacting the sampling rate (SR), i.e., the volume of air that is effectively stripped of gaseous mercury per unit of time. We measured the SR of a recently calibrated passive air sampler for gaseous Hg in the laboratory under varying wind speeds (wind still to 6 m s−1), temperatures (−15 to +35 °C), and relative humidities (44 to 80 %). While relative humidity has no impact on SR, SR increases slightly with both wind speed (0.003 m3 day−1 increase in SR or 2.5 % of the previously calibrated SR for every m s−1 increase for wind speeds > 1 m s−1, typical of outdoor deployments) and temperature (0.001 m3 day−1 increase in SR or 0.7 % for every 1 °C increase). The temperature dependence can be fully explained by the effect of temperature on the molecular diffusivity of gaseous mercury in air. Although these effects are relatively small, accuracy can be improved by adjusting SRs using measured or estimated temperature and wind speed data at or near sampling sites. We also assessed the possibility of reusing Radiello® diffusive barriers previously used in the passive air samplers. The mean rate of gaseous Hg uptake was not significantly different between new and previously used diffusive barriers in both lab and outdoor deployments, irrespective of the applied cleaning procedure. No memory effect from Radiellos® previously deployed in a high Hg atmosphere was observed. However, a loss in replicate precision for the dirtiest Radiellos® in the indoor experiment suggests that cleaning is advisable prior to reuse.
Highlights
Fine spatial resolution measurements of atmospheric contaminants are difficult and expensive, especially at remote locations and in developing countries
The sampling rate (SR) of the standard configuration passive air samplers (PASs) deployed outdoors of 0.121 m3 day−1 was obtained for a mean wind speed of 1.89 m s−1 and a mean temperature of 7.6 ◦C.15
While we presently do not know the reason for this discrepancy, it may be related to the relatively short deployment periods used in the present experiments
Summary
Fine spatial resolution measurements of atmospheric contaminants are difficult and expensive, especially at remote locations and in developing countries. In order for a PAS to yield volumetric air concentration data, a sampling rate (SR), i.e., the volume of air that is effectively stripped of the contaminant of concern per unit of time, needs to be derived. This is done either in calibration experiments that deploy the PAS concurrently with reliable active sampling techniques or theoretically based on an understanding of the processes controlling mass transfer from atmosphere to PAS sorbent (Armitage et al, 2013; Gustin et al, 2011; Skov et al, 2007). A reliable PAS requires that the impact of various factors influencing the SR is, in order of preference, either eliminated, minimized, or quantifiable and predictable
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