Passive air sampling of gaseous elemental mercury: a critical review

Abstract. Because gaseous elemental mercury (GEM) is distributed globally through the atmosphere, reliable means of measuring its concentrations in air are important. Passive air samplers (PASs), designed to be cheap, simple to operate, and to work without electricity, could provide an alternative to established active sampling techniques in applications such as (1) long-term monitoring of atmospheric GEM levels in remote regions and in developing countries, (2) atmospheric mercury source identification and characterization through finely resolved spatial mapping, and (3) the recording of personal exposure to GEM. An effective GEM PAS requires a tightly constrained sampling rate, a large and stable uptake capacity, and a sensitive analytical technique. None of the GEM PASs developed to date achieve levels of accuracy and precision sufficient for the reliable determination of background concentrations over extended deployments. This is due to (1) sampling rates that vary due to meteorological factors and manufacturing inconsistencies, and/or (2) an often low, irreproducible and/or unstable uptake capacity of the employed sorbents. While we identify shortcomings of existing GEM PAS, we also reveal potential routes to overcome those difficulties. Activated carbon and nanostructured metal surfaces hold promise as effective sorbents. Sampler designs incorporating diffusive barriers should be able to notably reduce the influence of wind on sampling rates.