Hydrogen Sulphide (H2S) and Total Reduced Sulphur (TRS)
Hydrogen sulphide (H2S) is a colourless gas with a rotten
egg odour. Total reduced sulphur (TRS) includes hydrogen sulphide, mercaptans,
dimethyl sulphide, dimethyl disulphide and other sulphur compounds.
Sulphur dioxide is not included in the determination of TRS. Industrial
sources of H2S and TRS include fugitive emissions (leakages)
from petroleum refineries, tank farms for unrefined petroleum products,
natural gas plants, petrochemical plants, oil sands plants, sewage treatment
facilities, pulp and paper plants that use the Kraft pulping process,
and animal feedlots. Natural sources of H2S include sulphur
hot springs, sloughs, swamps and lakes.
Monitoring Method
H2S is measured continuously by pulsed fluorescence (the
same principle as the SO2 analyzer). Initially, all SO2
in the air sample is scrubbed out so that it does not interfere with
the measured H2S concentration. The remaining H2S
in the sample is then converted to SO2. The sample is then
drawn through a sample chamber where it is irradiated with pulses of
ultra-violet light. Any SO2 in the sample is excited to a
higher energy level and upon returning to its original state, light
or fluorescence is released. The amount of fluorescence measured is
proportional to the SO2 (converted from H2S or
TRS) concentration. The TRS analyzer works on exactly the same principle
as the H2S analyzer. The only difference is that the conversion
of sulphur compounds to SO2, occurs at a much higher temperature.
Therefore there is a more complete conversion of sulphur compounds to
SO2.
Objectives
The Objectives for H2S are based on the odour. However, some
individuals can smell H2S at levels below the ambient Objectives.
The Objectives for hydrogen sulphide in Alberta are:
- 0.010 ppm as a 1-hour average concentration; and
- 0.003 ppm as a 24-hour average concentration.
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