scope:

Introduction

Mercury is present in ambient air both in elemental and in inorganically and organically bound form. The background mass concentrations of mercury in unpolluted air masses vary from 1 ng/m³ to 4 ng/m³ [1; 2; 3; 4]. In the urban air and in the vicinity of mercury emission sources, significantly higher mass concentrations have been measured.

Owing to the long dwell time of elemental mercury in the atmosphere, it accounts for the major part (> 90%) of the entire atmospheric mercury in industry-remote air masses. However, in the immediate vicinity of emission sources, the situation may be different.

Mercury occurs in the air in the form of particulate and gaseous mercury. In clean marine and continental air, the mass concentration of particulate mercury is two orders of magnitude lower than the total mercury mass concentration [1; 2]. The particulate share in the urban air is usually well below 10 %, whilst higher particulate shares can be found at contaminated sites [3; 5; 6;]. The gaseous share consists for the most part of elemental mercury [1; 3; 7]; in addition, methyl mercury chloride (MMC), dimethyl mercury (DMM) and mercury(II) chloride (MC) may also occur in small quantities as volatile mercury compounds [1; 8].

The Guideline series VDI 2267 describes methods for determining the ambient air concentration of metals and semimetals entering the atmosphere from firing plants as well as during their production and processing. This includes mercury, the metal treated in this Guideline. As a result of chemical reactions, attachment or condensation, the vast majority of the metals and semimetals treated in the other parts of Guideline series VDI 2267 occur as inorganic compounds in particulate form or attached to dust particles; this also gives the Guideline series its title of "Determination of suspended particles in ambient air". Although this does not quite apply to mercury with a particulate share of only a few per cent (see above and Annex B), this Guideline is nevertheless published for systematic reasons in Guideline series VDI 2267.

This Guideline describes a method for determining the mass concentration of the total gaseous mercury (TGM) in ambient air. No distinction is made between elemental, or inorganically or organically bound mercury. Owing to the low mass concentrations of TGM sampling by enriching is employed. Analytic determination is carried out after thermal desorption with the aid of atomic absorption spectrometry (AAS).