Natural sources of hydrogen sulphide include sulphur hot springs, sloughs, swamps and lakes. Methane, a non-reactive hydrocarbon, is the most common hydrocarbon in the earth's atmosphere. Sources of hydrocarbons include vegetation, vehicular emissions, gasoline marketing and storage tanks, petroleum and chemical industries, dry cleaning, fireplaces, natural gas combustion and aircraft traffic. Hydrocarbon concentrations are highest in the winter months at monitoring stations which are located close to major traffic arteries. In downtown Edmonton and Calgary, maximum hydrocarbon values are observed during the morning and afternoon rush hours.
Vehicles are the major source of hydrocarbons at urban locations.
Natural background hydrocarbon concentration ranges from 1.5 to 2.0 ppm Carbon Dioxide Carbon dioxide is a colourless, odourless, non-toxic gas that is produces by man through the combustion of fossil fuels. Some natural sources of carbon dioxide include volcanoes, forest fires and the respiration processes of microorganisms and plants. Carbon dioxide emissions comprise over half of the greenhouse gases emitted by man. Ammonia Ammonia is a colourless gas with a pungent odour. Ammonia is emitted into the atmosphere through natural sources such as the deterioration of plant and animal matter and man-made sources such as the fertilizer industry.