A HgCl₂ containing diffusion source was evaluated for its potential usefulness as a calibration source for gaseous oxidized mercury (GOM) measurements. Unlike previous calibration sources described in the literature, this source made use of a flow rate of at least 1 L min-¹, and was maintained at a temperature of as low as - 15oC. Under these conditions, the source was found to emit GOM at an environmentally relevant level of 0.0905 pg s-¹, with a GOM fraction of approximately 78%. The source was found to have a consistent response to temperature, a steady state emission level of Hg could be rapidly established and the source was temporally stable. Duplicate sources were compared with one another and found to emit similar levels of Hg under identical sampling conditions. Various methods of cleaning HgCl₂ contaminated items were tested, with the most successful method using a stannous chloride wash solution.