Detection and determination of volatile metal compounds in the atmosphere by a Mist-UV sampling system

A newly developed system (Mist-UV sampling system) to simultaneously trap and detect metal compounds in the atmosphere is described. Metals present in atmospheric samples as volatile metal compounds (VMCs), including those associated with condensation mode particles, are simultaneously oxidized by ultraviolet (UV) irradiation (low-pressure mercury lamp) and dissolved in nitric acid mist in an oxidation chamber. Air is first passed through a 0.2 μm filter and then mixed with a nitric acid mist and exposed to UV radiation after which it is passed through a nitric acid trap. After trapping, the inorganic metals resulting from the VMCs and particulates are quantitatively determined using inductively coupled plasma-mass spectrometry (ICP-MS). After development, this sampling system was applied directly to the quantitation of VMCs in ambient air in Auckland, New Zealand. The trapping efficiency of the Mist-UV sampling system was over 69% for each of the seven different metals that were detected in the atmosphere (Mg, Al, Ga, Sr, Ba, Hg and Pb). Key results obtained were: Mg concentrations were found to be higher than concentrations associated with particulate in remote air (range: 0.36–1.6 μg m−3); Al and Sr existed as VMCs unaffected by UV; UV oxidized Hg provided the total concentration of Hg detected. The characteristics of the Mist-UV sampling system suggest that it can be used as a tool to determine volatile metals, metal clusters and metals associated with particulates <0.2 μm in diameter especially in polluted atmospheres. This is a relatively new area, and the information gained is of particular relevance to metal transport and deposition.