Sulphur dioxide is a strong smelling, colourless gas formed by the smelting of sulphur-containing ores or the burning of sulphur-containing fuels. Sulphur dioxide contributes to acid rain, damages vegetation, and may cause coughs, asthma, bronchitis, and eye irritation.
Sulphur dioxide can affect both plants and people. Plants are more sensitive than people to sulphur dioxide and are affected by lower levels of sulphur dioxide in the air.
Sulphur dioxide irritates the nose and throat. Effects on healthy individuals include an increased breathing rate or an increased resistance to airflow. These effects have not been observed for short-term sulphur dioxide exposure levels below about 1 ppm (parts per million)1. Asthmatics and exercising individuals are more sensitive to sulphur dioxide than non-exercising healthy individuals. For exercising asthmatics, increased resistance to airflow, coughing and wheezing have been observed at sulphur dioxide concentrations as low as 0.40 ppm.
The lowest level at which sulphur dioxide can be detected by taste or smell is estimated to be in the range from 0.30 to 1.0 ppm.
For longer exposures, sulphur dioxide levels above 0.15 ppm have been linked with increased hospital admissions for cardiac or respiratory illnesses. Long-term exposures to 0.027 to 0.031 ppm of sulphur dioxide with high levels of particulate matter in the air have been associated with an increase in respiratory illnesses in children.
1 One ppm is the same as one drop of water in 220 gallons or 6 barrels of water.
With plants, the leaves or needles are the first to be damaged by exposure to high sulphur dioxide levels. Stems and buds are more resistant to harmful effects. The sensitivity of a plant is also affected by the species of plant, amount of sunlight, temperature, humidity levels, soil moisture levels and stage of plant growth.
For example, jack pine, a moderately sensitive species of tree, has shown injury following a two-hour exposure to 0.25 ppm. A one-hour exposure to 0.25 ppm sulphur dioxide has been shown to injure begonias, while a four-hour exposure to the same level of sulphur dioxide has damaged broccoli.
The metallurgical smelter operated by the Hudson Bay Mining and Smelting Company in Flin Flon accounts for about 49% of the province's man-made emissions of sulphur dioxide into the atmosphere. In 1994, the total sulphur dioxide emissions in the province were estimated to be 398,000 tonnes. The total sulphur dioxide emissions were less than the 550,000 tonne sulphur dioxide emission limit agreed to under the national Acid Rain Program.
Manitoba has established ambient air quality objectives for sulfur dioxide. These levels are set to provide adequate protection against effects on soil, water, vegetation, materials, animals, visibility, personal comfort and well-being. These air quality objectives and their basis are shown in the following table:
Air Quality Objectives for Sulphur Dioxide over a Continuous Period
|0.34 ppm||0.11 ppm||0.02 ppm|
|Prevents taste and odour discomfort to sensitive individuals.||Prevents health effects if particulate matter also low in air; in conjunction with 1-hour objective, will prevent persistence of concentrations that may injure plants.||Minimizes the occurrence of chronic effects in natural forests.|
The Hudson Bay Mining and Smelting Company in Flin Flon operates a public air quality warning system based on the air quality objectives. This system advises residents when elevated levels of sulphur dioxide are present in the community.
A Level 1 Public Warning is issued when any two consecutive 15-minute average sulphur dioxide concentrations are greater than 0.34 ppm. This warning is primarily directed at those who are sensitive to respiratory irritants. A Level 2 Public Warning is issued when any 1-hour average concentration of sulphur dioxide is greater than 0.34 ppm. This warning is directed to the entire population.
Warnings are broadcast on the local radio station. Warnings can also be obtained by calling 687-2360 at any time.
Completed in 1993, the new zinc pressure leaching plant at the Hudson Bay Mining and Smelting Company has reduced sulphur dioxide emissions by 30% and particulate emissions by nearly 75%. As a result, there has been some improvement in local air quality. However, some episodes of elevated sulphur dioxide still occur. These episodes occur during "inversions" - weather conditions that don't allow emissions to disperse but instead force the plume from the smelter stack to the ground level. Fugitive spill gases also have an impact on downtown air quality.
Individuals at risk include those who have asthma or other respiratory illnesses, the elderly and children.
Specific health concerns that you feel may be a result of local air quality should be referred to your family doctor.
A 1993 study of health care use found a higher incidence of doctor visits and hospitalization for respiratory illness in Flin Flon compared to the rest of Manitoba. To minimize personal exposure to sulphur dioxide, consideration should be given to the messages issued by the air quality warning system.
Level 1 and Level 2 Warnings are issued to the public when sulphur dioxide levels are elevated in the community. When a Level 1 Warning is issued, individuals predisposed to respiratory difficulties may feel some discomfort. When a Level 2 Warning is issued, all individuals may feel some discomfort.
The following suggestions may help relieve some symptoms: