Determining the Reporting Threshold for Total Reduced Sulphur Using Equivalence Factors

Total reduced sulphur (TRS) refers to a gaseous mixture of compounds containing one or more sulphur atom in its reduced state. For the purposes of reporting to the National Pollutant Release Inventory (NPRI), this class of substances is restricted to the substances listed in Table 1. Note that three of these TRS compounds (H2S, CS2 and COS) are also listed individually under Part 1A. If any of these substances meets the 10 tonne reporting threshold alone, then it must also be reported individually.

Table 1. Total Reduced Sulphur Substances
Substance NameChemical FormulaChemical Abstracts Service Registry NumberHydrogen Sulphide Equivalence Factor
Hydrogen sulphide
Carbon disulphide
Carbonyl sulphide
Dimethyl sulphide
Methyl mercaptan
Dimethyl disulphideC2H6S2624-92-00.724

When determining the reporting threshold and reporting to the NPRI, TRS must be expressed in terms of hydrogen sulphide (H2S). TRS quantities can be determined using several methods, including summing H2S equivalencies, emissions monitoring or source testing. This document explains how to determine the reporting threshold for TRS using H2Sequivalence factors.

To use the equivalence factor method, the equivalency of the individual TRScompounds in tonnes of H2S must be determined and added together to determine if TRS is required to be reported. The H2Sequivalence factors are listed in the table above.

Example of Calculating the Reporting Threshold for Total Reduced Sulphur:

The following table illustrates the calculation of the reporting threshold for TRS. To calculate emissions expressed as H2S, add the quantities of the substances multipled by their H2S equivalence factor:

TRS = H2S + (CS2 × 0.895) + (COS × 0.567) + (C2H6S × 0.548) + (CH4S × 0.708) + (C2H6S2× 0.724)

Table 2. Total Reduced Sulphur Reporting Threshold Example Calculation
Substance NameChemical FormulaQuantity
Equivalence Factor
(tonnes H2S)
Hydrogen sulphideH2S31.0003.000
Carbon disulphideCS220.8951.790
Carbonyl sulphideCOS220.56712.481
Dimethyl sulphideC2H6S40.5482.194
Methyl mercaptanCH4S20.7081.417
Dimethyl disulphideC2H6S260.7244.341
Total reduced sulphur (expressed as H2S)25.223

In this example, a report is required (assuming the facility also meets the 20 000 hour employee threshold or an activity to which the employee threshold does not apply takes place at the facility), because the total amount of TRS exceeded 10 tonnes for the calendar year. In addition, carbonyl sulphide must be reported separately, since the 10 tonne threshold was met and COS is listed separately in Part 1A.

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