Mercury in ambient air

The chemistry of mercury, in reference to its behavior in the atmosphere, is more complex compared to other heavy metals. Main forms are: elemental mercury vapor (Hg0, called even or zerovalent metallic mercury), mercury vapor divalent (Hg22+ mercurous, or Hg2+ mercuric), organic mercury (especially methylmercury, MeHg). A fourth form could be considered, different under the chemical profile, whose characteristic is physical: mercury bound to particulate (HgP), in the form of Hg0 and Hg2+. In general, analyses on ambient air are performed on the Total Gaseous Mercury (TGM) which is defined as the fraction passing a 0.45 μm filter; TGM is mainly composed of elemental Hg0 vapour, with minor fractions of other volatile forms as HgCl2, CH3HgCl or (CH3)2Hg. Measurements carried out at background sites reveal that the TGM corresponds almost to total mercury (>99%) in atmosphere. Global anthropogenic emission for North America, Europe and East Europe areas data indicate that stationary combustion processes, are responsible of about 60-75% of all mercury emitted, mainly because of its content in coal, for a total of 2000 tons/year. About 50 % of emissions from combustion of fossil fuels is constituted by Hg0, 40 % of Hg2+ and 10 % of HgP. Mercury is therefore assumed as a tracer of coal combustion emission. The official Italian sampling and analysis procedure (DLgs 155/10 - UNI EN 15852) has been tested as is, and modified in order to improve the analytical performance, reduce the timing requirement and reduce the related cost. All the variations introduced have been thoroughly investigated in order to exclude any negative effect on the standard performances.