The effects of meteorological parameters and diffusive barrier reuse on the sampling rate of a passive air sampler for gaseous mercury

摘要

Passive air sampling of gaseous mercury (Hg) requires a highlevelof accuracy to discriminate small differences in atmosphericconcentrations. Meteorological parameters have the potential todecrease this accuracy by impacting the sampling rate (SR), i.e.,the volume of air that is effectively stripped of gaseous mercuryper unit of time. We measured the SR of a recently calibratedpassive air sampler for gaseous Hg in the laboratory under varyingwind speeds (wind still to 6 m s), temperatures (−15to +35 °C), and relative humidities (44 to80 %). While relative humidity has no impact on SR, SR increasesslightly with both wind speed (0.003 m dayincrease in SR or 2.5 % of the previously calibrated SR forevery m s increase for wind speeds   1 m s, typical of outdoor deployments) andtemperature (0.001 m day increase in SR or0.7 % for every 1 °C increase). The temperaturedependence can be fully explained by the effect of temperature onthe molecular diffusivity of gaseous mercury in air. Although theseeffects are relatively small, accuracy can be improved by adjustingSRs using measured or estimated temperature and wind speed data ator near sampling sites. We also assessed the possibility of reusingRadiello diffusive barriers previously used inthe passive air samplers. The mean rate of gaseous Hg uptake was notsignificantly different between new and previously used diffusivebarriers in both lab and outdoor deployments, irrespective of theapplied cleaning procedure. No memory effect fromRadiellos previously deployed in a high Hgatmosphere was observed. However, a loss in replicate precision forthe dirtiest Radiellos in the indoor experimentsuggests that cleaning is advisable prior to reuse.