Ontario air standard for total reduced sulphur

Ontario Air Standard For Total Reduced Sulphur

June 2007

Standards Development Branch Ontario Ministry of the Environment

Ontario

Ontario Air Standards for Total Reduced Sulphur

Executive Summary
The Ontario Ministry of the Environment (MOE) has identified the need to develop and/or update air quality standards for priority contaminants. The Ministry’s Standards Plan, which wasreleased in October, 1996 and revised in November, 1999, identified candidate substances for which current air quality standards will be reviewed or new standards developed. Total reduced sulphur was identified as a priority for review based on both its pattern of use in Ontario and toxicological information that has been published subsequent to the development of the existing standard in 1977.Once a decision is made on the air standards, they will be incorporated into Ontario Regulation 419: Air Pollution – Local Air Quality (O. Reg. 419/05). The Ambient Air Quality Criterion (AAQC) will be incorporated into Schedule 3 of the regulation and the half hour standards will be incorporated into Schedule 2. An ‘Information Document’ containing a review of scientific and technical informationrelevant to setting an air quality standard for total reduced sulphur was previously posted on the Environmental Bill of Rights Registry for public comments. This was followed more recently by the posting of a document providing the rationale (‘Rationale Document’) for recommending an Ambient Air Quality Criterion (AAQC) and a half hour standard for total reduced sulphur. This document, referred toas the ‘Decision Document’, summarizes the comments received from stakeholders on the proposed standards and the Ministry responses to these comments. This document also provides the rationale for the decision on the air quality standards for total reduced sulphur. Total reduced sulphur (TRS) is a mixture of reduced sulphur compounds, primarily composed of hydrogen sulphide (H2S), mercaptans(typically represented by methyl mercaptan), dimethyl sulphide (DMS), and dimethyl disulphide (DMDS). Hydrogen sulphide and methyl mercaptan are both colourless gases, with strong and unpleasant odour. Dimethyl sulphide and DMDS are colourless liquids, with strong unpleasant sulphur odours. Hydrogen sulphide is used as an analytical reagent and an intermediate in the production of other reduced sulphurcompounds, sulphuric acid, and in the precipitation of sulphides from metals. Other uses are as agricultural disinfectants, metallurgical applications, and large quantities of H2S are used in the production of heavy water, for use in nuclear power reactors. Hydrogen sulphide is also a by-product of various natural and industrial processes, including microbial degradation, the refining of oil andpetroleum, and in the kraft process of producing wood pulp.

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Ontario Air Standards for Total Reduced Sulphur

Methyl mercaptan has been used as an odourant for natural gas, as an intermediate in the production of pesticides and jet fuel, and in the synthesis of methionine and plastics. It is produced as a by-product of the degradation of organic matter, and various industrial processes,including the kraft pulping process. Dimethyl sulphide is used as an intermediate in the synthesis of dimethyl sulphoxide, as a catalyst preactivator, as a gas odourant, and as a solvent for anhydrous mineral salts. Dimethyl disulphide is used as a sulphating agent for certain industrial catalysts and also as a food flavouring agent. Both DMS and DMDS are found in food products, and form asby-products of various industrial processes. The National Pollutant Release Inventory (NPRI) did not require reporting on TRS or its components, except for hydrogen sulphide, prior to 2005. In 2005, Environment Canada started to report releases of TRS from Ontario facilities on the NPRI. Since 2000, industries have been required to report releases of hydrogen sulphide in Canada. The available data...