Air Pollutants

OZONE

• O3 is a colourless, odourless gas at ambient concentrations and is a major component of smog. Ground-level ozone is not emitted directly into the atmosphere. It results from photochemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOCs) in the presence of sunlight. High levels typically occur from May to September, between noon and early evening.

Ontario Volatile Organic Compounds Emissions by Sector
(Emissions from Point/Area/Transportation Sources, 2006 Estimates)

PARTICULATE MATTER 

• Particulate matter is characterized according to size - mainly because of the different health effects associated with particles of different diameters. Particulate matter is the general term used for a mixture of solid particles and liquid droplets in the air. PM2.5 in Ontario is largely made up of sulphate and nitrate particles, elemental and organic carbon and soil.
• PM2.5 material is primarily formed from chemical reactions in the atmosphere and through fuel combustion (e.g., motor vehicles, power generation, industrial facilities, residential fire places, wood stoves and agricultural burning).  
• Significant amounts of PM2.5 are carried into Ontario from the U.S. During periods of widespread elevated levels of fine particulate matter, it is estimated that more than 50 per cent of Ontario's PM2.5 comes from the U.S.

Ontario PM2.5 Emissions by Sector 
(Emissions from Point/Area/Transportation Sources, 2006 Estimates)  

NITROGEN DIOXIDE

• NO2 is a reddish-brown gas with a pungent and irritating odour. It transforms in the air to form gaseous nitric acid and toxic organic nitrates. NO2 also plays a major role in atmospheric reactions that produce ground-level ozone, a major component of smog. It is also a precursor to nitrates, which contribute to increased respirable particle levels in the atmosphere. All combustion in air produces oxides of nitrogen (NOx), of which NO2 is a major product.

Ontario Nitrogen Oxides Emissions by Sector 
(Emissions from Point/Area/Transportation Sources, 2006 Estimates)
 
SULPHUR DIOXIDE

• SO2 is a colourless gas. It smells like burnt matches. It can be oxidized to sulphur trioxide, which in the presence of water vapour is readily transformed to sulphuric acid mist (aka acid rain).

Ontario Sulphur Dioxide Emissions by Sector
(Emissions from Point/Area/Transportation Sources, 2006 Estimates)
 
CARBON MONOXIDE

• CO is a colourless, odourless and tasteless but poisonous gas produced primarily by incomplete burning of fossil fuels.

Ontario Carbon Monoxide Emissions by Sector 
(Emissions from Point/Area/Transportation Sources, 2006 Estimates)
 
TOTAL REDUCED SULPHUR COMPOUNDS

• (TRS) compounds produce offensive odours similar to rotten eggs or cabbage. Industrial sources of TRS include the steel industry, pulp and paper mills, refineries and sewage treatment facilities. Natural sources include swamps, bogs and marshes. TRS compounds are not normally considered a health hazard. They are, however, a primary cause of odours.