Sulphur dioxide is formed during the processing and combustion of fossil fuels containing sulphur. It is a colourless gas with a pungent odour, and can be detected by taste and odour at concentrations as low as 300 ppb. Sulphur dioxide reacts in the atmosphere to form sulphuric acid and acidic aerosols, which contribute to acid rain. Sulphur dioxide combines with other atmospheric gases to produce fine particles, which may reduce visibility.
Brief exposure to high concentrations of sulphur dioxide and its products can produce human health effects, irritating the upper respiratory tract and aggravating existing cardiac and respiratory disease. Long-term exposure may increase the risk of developing chronic respiratory disease.
Sensitive vegetation may be injured by exposure to high sulphur dioxide concentrations. Symptoms include a chlorotic appearance of the leaf with silvering or bronzing of the underside.
The inventory of emissions within the West Central Regional Airshed Zone was updated based on 1999 data. The inventory includes measurements made by Alberta Environment and emissions calculated from the Alberta Energy and Utilities Board records of fuel usage and flare volumes. Large emission sources that contribute pollutants to the airshed, but are located outside of its boundaries, are excluded. There was an estimated 8% increase in ppb emissions within the West Central Airshed Zone from 1998 to 1999. It is estimated that sulphur dioxide emission whith the Zone in 1999 totalled 26,880 tonnes. The oil and gas sector emitted 97% of the sulphur dioxide within the airshed with nine large sour gas processing plants contributing about 90% of the total emissions. Other sectors are relatively small emitters of ppb with forestry contributing about two percent of the total.
Alberta Environment has adopted the Environment Canada's most rigorous objectives for sulphur dioxide. The Alberta guidelines for ambient air are:
| Concentration (ppb) | Exposure Time | Human Symptoms and Other Effects |
|---|---|---|
| 400,000 | — | Lung edema; bronchial inflammation |
| 20,000 | — | Eye irritaiton; coughing in health adults |
| 15,000 | 1 hour | Decreased mucoduar-y activity |
| 10,000 | 10 min | Bronchospasm |
| 10,000 | 2 hours | Visible foliar injury to vegetation in arid regions |
| 8,000 | — | Throat irritation in healthy adults |
| 5,000 | 10 min | Increased airway resistance in healthy adults at rest |
| 1,000 | 10 min | Increased airway resistance in asthmatics at rest and in healthy adults at exercise |
| 1,000 | 5 min | Visible injury to sensitive vegetation in humid regions |
| 500 | 10 min | Increased airway resistance in asthmatics at exercise |
| 500 | — | Odour threashold |
| 500 | 1 hour | Visibile injury to sensitive vegetation in humid regions |
| 500 | 3 hours | US national secondary ambient air quality standard |
| 200 | 3 hours | Visible injury to sensitive vegetation in humid regions |
| 190 | 24 hours | Aggravation of chronic respiratory disease in adults |
| 172 | 1 hour | Alberta ambient air quality guideline |
| 140 | 24 hours | US national primary ambient air quality standard |
| 70 | annual | Aggravation of chronic respiratory disease in children |
| 57 | 24 hours | Alberta ambient air quality guideline |
| 30 | annual | US national primary ambient air quality standard |
| 11 | annual | Alberta ambient air quality guideline |
Oxides of nitrogen, mostly in the form of nitrogen oxide (NO) and nitrogen dioxide (NO2), are produced by the high temperature combustion of fossil fuels. Nitrogen oxide is the predominant species emitted by combustion sources but it is rapidly changed to nitrogen dioxide in the atmosphere.
Nitrogen dioxide is a reddish-brown gas with a pungent irritating odour. It has been linked to respiratory disease and contributes to acid rain. It plays a major role in atmospheric photochemical reactions and ground level ozone formation and destruction.
Exposure of vegetation to high concentrations of nitrogen oxides results in silvering of the lower leaf surface. A waxy appearance appears shortly after exposure followed by bronzing after two or three days.
Emissions of nitrogen oxides within the West Central Regional Airshed Zone, excluding transport from outside the zone, were estimated to be 29,800 tonnes in 1999. Major sources were the oil and gas sector, followed by railways and highways. Together, these three sectors contributed to about 87% of the total NOX emissions. Of the oil and gas sector emissions, 60% of the NOX was emitted by gas processing plants and 40% by compressor stations. These estimates do not include nearby major sources of NOX located outside the zone.
Computer modeling studies, conducted for the WCAS prior to establishment of the zone, indicated that 60% of the nitrogen deposited within the zone originates from outside the zone boundaries.
Alberta Environment guideline are based on the prevention of human health effects. They are equal to the most rigorous of Environment Canada's ambient air quality objectives. The Alberta Guidelines for nitrogen dioxide, the major component of nitrogen oxides in the ambient atmosphere are:
| Concentration (ppb) | Exposure Time | Human Symptoms and Other Effects |
|---|---|---|
| 300,000 | — | Rapid death |
| 150,000 | — | Death after 2 or 3 weeks by bronchiolitis fibrosa obliterans |
| 50,000 | — | Reversible, nonfatal bronchiolitis |
| 10,000 | — | Impairment of ability to detect odour of NO2 |
| 5,000 | 15 min | Impairment of normal transport of gases between the blood and lungs in health adults |
| 2,500 | 2 hours | Increased airway resistance in healthy adults |
| 2,000 | 4 hours | foliar injury to vegetation |
| 1,000 | 15 min | Increased airway resistance in adults with bronchitis |
| 1,000 | 48 hours | Slight leaf spotting of pinto bean, endive, and cotton |
| 300 | — | Brownish color of target — 1 km distant |
| 250 | — | Decrease of growth and yeild of tomatoes and oranges |
| 212 | 1 hour | Alberta ambient air quality guideline |
| 200 | 8 hours | Yellowing of white fabrics |
| 120 | — | Odour perception threshold |
| 106 | 24 hours | Alberta ambient air quality guideline |
| 100 | 12 weeks | Fading of dyes on cotton and rayon |
| 100 | 20 weeks | Reduction of growth of Kentucky bluegrass |
| 32 | annual | Alberta ambient air quality guideline |
| 30 | — | Brownish color of target — 10 km distant |
| 3 | — | Brownish color of target — 100 km distant |
Ozone is both a natural component of the atmosphere and a major constituent of photochemical smog. At normal atmospheric concentrations it is an odourless, colorless gas. However, at concentrations higher than one ppm, such as found near photocopier machines and near electrical discharges, it has a sharp odour.
Ozone is a strong oxidizer and can irritate eyes, nose and throat and decrease athletic performance. High concentrations can increase susceptibility to respiratory disease and reduce crop yields.
Unlike other pollutants, ozone is not emitted directly into the atmosphere but is produced through a series of chemical reactions in the atmosphere. Concentrations are controlled mainly by emissions of nitrogen oxides and reactive hydrocarbons. These reactions may lead to an increase in ozone concentrations or, as in the case of Alberta cities, a decrease. Ozone is a natural component of the upper atmosphere and may be transported to ground level by meteorological processes.
Alberta Environment guidelines for ozone are:
Provincial and federal guidelines are currently under review.
| Concentration (ppb) | Exposure Time | Human Symptoms and Other Effects |
|---|---|---|
| 10,000 | — | Severe pulmonary edema; possible acute bronchiolitis; decreased blood pressure; rapid weak pulse |
| 1,000 | — | Coughing; extreme fatigue; lack of coordination; increased airway resistance; decreased forced expiratory volume |
| 500 | — | Chest constriction; impaired carbon monoxide diffusions capacity; decrease in lung function without exercise |
| 300 | — | Headache; chest discomfort sufficient to prevent completion of exercise; decrease in lung function in exercising subjects |
| 250 | — | Increase in incidence and severity of asthma attacks; moderate eye irritation |
| 150 | — | For sensitive individuals, reduction in pulmonary lung function; chest discomfort; irritation of the respiratory tract, coughing and wheezing |
| 150 | — | Threshold for injury to vegetation |
| 120 | — | US national primary and secondary ambient air quality standard |
| 100 | — | Maximum allowed by OSHA in industrial work areas |
| 82 | 1 hour | Alberta ambient air quality guideline |
| 50 | — | Maximum recommended by ASHRAE in an air conditioned and ventilated space |
| 20–40 | — | Range in which ozone occurs in healthy outdoor environments. Also ozone level produced by some indoor air ionizers when operated according to instructions. |
| 3–10 | — | Low range at which average person can smell ozone |
| 1 | — | Most indoor environments — windows open |
Ambient particulate matter consists of a mixture of particles of varing size and chemical composition. Particles that are less than 10 micrometers in diameter (PM10) can be inhaled. The fraction of particles, which are less than 2.5 micrometers in diameter (PM2.5) can be trapped in the airways and lungs and is believed to cause adverse health effects. Fine particles (PM2.5) also reduce visibility and can contribute to acidification of soils.
Sources of PM10 size particles include windblown soil, road dust, and industrial activities. PM2.5 size particles are formed from gases released to the atmosphere by combustion processes such as from motor vehicles, power plants, gas processing plants, compressor stations, household heating, and forest fires.
Guidelines for ambient atmospheric concentrations of PM10 and PM2.5 size particles are under consideration by the Alberta and federal governments. A provisional Canada-Wide Standard has been adopted for PM2.5 of 30 µg/m3, 24-hour averaging time, by the year 2010.
Hydrocarbons are divided into two broad categories, "non-reactive" and "reactive" hydrocarbons. The major non-reactive hydrocarbon is the atmosphere is methane, which is a naturally occurring colorless, odourless gas recognized as a major contributor to the greenhouse effect. The reactive hydrocarbons consist of many volatile organic compounds, some of which react with oxides of nitrogen in the atmosphere to form ozone. They generally occur at much lower concentrations than methane. Total hydrocarbons (THC) include both reactive and non-reactive hydrocarbons.
Large amounts of methane are produced naturally through the decay of vegetation but human activity is contributing to a worldwide increase in methane concentrations of about 1% per year. Trees and plants are major natural emitters of reactive hydrocarbons with other significant sources being motor vehicle exhaust, gasoline handling and the petroleum and chemical industries.
There are no Alberta guidelines for ambient hydrocarbon concentrations.
Low concentrations of pollutants that cannot be monitored by continuous monitors can be measured using an integrated sampling method. Samples are collected over a two-week period to obtain suitable concentrations, and then analyzed in a laboratory. Ammonia is one such gas. It is a colorless gas with a pungent odour which is produced by natural anaerobic decay processes.
Major agricultural sources are animal wastes from the cattle industry and the fertilizers widely applied by the grain industry.
Air quality depends on the rate that pollutants are emitted to the atmosphere and the rate at which these pollutants are dispersed away from the sources. Air pollution transport and dispersion are influenced by wind speed and direction, the temperature structure of the atmosphere, the solar cycle, turbulence, precipitation and changes in these elements induced by local topography.
Precipitation may remove pollutants from the atmosphere, depositing them on soils and vegetation. Rates of deposition of pollutant gases are highest when vegetation and soils are wet. Vegetation is more susceptible to damage during periods of highest growth.
Meteorlogical parameters measured in support of the West Central Airshed Society air quality monitoring program are:
Precipitation samples are also collected and chemically analyzed for acidity and major constituents.
The amount of a pollutant flushed from the atmosphere by precipitation (wet deposition) or deposited to the landscape in the form of gases and particles (dry deposition) determines the eventual effect on the environment.
Precipitation removes some pollutants from the atmosphere, depositing them on soils and vegetation. Prolonged high rates of deposition of acidifying species may result in long-term acidification of susceptible soils and lakes. The ppb Management Project Team of CASA recommended that Alberta adopt critical and target loads for deposition of acidifying pollutants in order to protect aquatic and terrestrial ecosystems. The recommended method of determining the total acid input is based on the difference between the total wet and dry deposition of acidifying and neutralizing substances. A critical load of 0.25 kiloequivalents of total acidity per hectare per year (keq ha-1yr-1) was recommended to protect sensitive areas of the province from long-term harmful effects.
There are natural variations of acidity in soils (pH) within the growing season and from year to year. In order to determine any changes in soil acidity caused by atmospheric input, measurments must be made over an extended period of time. Soils data is being collected by the WCAS as a continuation of the soil monitoring work previously performed under the Brazeau-Pembina Sulphur Deposition and Agriculture Study 1989-1994.