What is sulphur dioxide?
Sulphur dioxide (SO2) is a colourless gas, belonging to the family of gases called sulphur oxides (SOx). SO2 smells like burnt matches. Natural sources of sulphur dioxide include releases from forest fires and biological decay. The most important man-made sources of sulphur dioxide are fossil fuel combustion, smelting, manufacture of sulphuric acid, conversion of wood pulp to paper, incineration of refuse and production of elemental sulphur. Coal burning is the single largest man-made source of sulphur dioxide.
SO2 and nitrogen oxides (NOx) are the main contributors to acid rain. Health effects caused by exposure to high levels of SO2 include eye and respiratory tract irritation, and worsening cardiovascular disease. SO2 can travel a considerable distance downwind in certain meteorological conditions. Short-term exposure to SO2 may cause respiratory distress, especially in sensitive individuals such as asthmatics.
UPDATED Sulphur Dioxide AAQC: The way SO2 data is categorized has changed
The Ontario Ministry of the Environment Conservation and Parks updated the Ambient Air Quality Criteria (AAQC) for Sulphur Dioxide (SO2 on March 20, 2018 to be more protective of human health. This change reflects a more up-to-date understanding of the health effects of SO2.
Because of this change, we have updated how the concentration levels are categorized and displayed for CASA website users. Measurements will still be categorized as good, moderate, poor or very poor to show how they compare with the updated ministry criteria.
Please note that data collected prior to March 20, 2018, when pulled from CASA, will still apply the original measurement categories.
This chart shows how the AAQC categories have changed for data collected before and after March 20, 2018:
||Prior to March 20, 2018
||March 20, 2018 and beyond
| 0 - 169 ppb
|| 0 - 40 ppb
| 169 - 250 ppb
|| 40 - 120 ppb
| 250 - 2000 ppb
|| 120 - 250 ppb
| >2000 ppb
|| >250 ppb
Air quality standards
MECP: 10- minute AAQC (Ambient Air Quality Criteria): 67 ppb (parts per billion) or 178 µg/m3
MECP: 1- hour AAQC (Ambient Air Quality Criteria): 40 ppb (parts per billion) or 106 µg/m3
MECP: Annual AAQC (Ambient Air Quality Criteria): 4 ppb (parts per billion) or 11 µg/m3
Ontario's Ambient Air Quality Criteria
Links- more information on SO2
Air Quality Ontario – Sulphur Dioxide
Environment and Climate Change Canada - Air - Sulphur Oxides - SOx