Performance of a new diffusive sampler for Hg0 determination in the troposphere

Abstract

Environmental context. Mercury is of concern to both the public and to the scientific community because it is found at high levels in some marine predators, prompting the US EPA and others to make guidelines restricting the consumption of some species. Most mercury in the environment is emitted to the atmosphere, but it is not known how it is transferred from the atmosphere to the marine environment. Therefore, it is important to study the connection between emission of mercury, its transport and removal from the atmosphere. We have developed a new sampler that is inexpensive, easy to use and with a sufficiently high detection limit that it can be used to measure the low mercury concentrations in the atmosphere at a reasonable time resolution. Abstract. Mercury behaves uniquely in the atmosphere due to its volatility and long lifetime. The existing methods for measuring atmospheric mercury are either expensive or labour intensive. The present paper presents a new measurement technique, the diffusive sampler, that is portable, inexpensive, easy to use, and does not need a power supply. The sampler is sufficiently sensitive that it can measure mercury at low ambient levels with an exposure time of 1 to 3 days. The sampler is based on the Radiello diffusive sampler, which was used to collect volatile organic compounds. In the present paper, the method is validated under controlled laboratory conditions. The uptake rate of the Radiello diffusive sampler is determined using known concentrations of gaseous elemental mercury, and is measured as a function of wind speed, relative humidity and temperature. The Radiello sampler has a detection limit of 0.14 ng m–3 for 1 day of exposure and thus can be used to measure mercury concentrations at the low levels found in ambient air. The Radiello sampler is therefore useful for mapping concentrations close to sources and sinks, in addition to ambient concentrations. For example, the sampler can be used to describe the geographical extent of Arctic mercury depletion episodes where gaseous elemental mercury is removed and stays close to 0 ng m–3 for days, and it can be a powerful tool for mapping gradients around point sources and other areas of interest.