Air quality processes research

Environment Canada’s air quality scientists conduct research on the physical and chemical processes that determine the chemistry of the atmosphere.  Scientists study the processes that govern how chemicals enter, move through, and exit from the atmospheric environment. The research falls into the categories of emission, transport, transformation, levels of chemicals in air, and deposition.


Chemicals enter the air from man-made sources, such as our cars, power generating stations and waste incinerators, and also from natural sources such as forests and volcanoes. Chemicals can also be stored in lake or ocean waters and soils and later released to the atmosphere.

Examples of Environment Canada’s Emission Research:

  • Collecting particulate matter in air and tracing it to its source in a process called source apportionment.
  • Using light detection and ranging (lidar) technology and research aircraft to directly test industrial emission plumes.
  • Studying natural or recycled mercury emissions from soils.
  • Collecting air samples at various heights over corn fields to measure the rate at which pesticides are released from the soil.


Once in the atmosphere, these chemicals are carried by winds from source areas (often cities) to other regions. Because winds do not recognize political boundaries, atmospheric transport can lead to transboundary air pollution, i.e. pollutants from one province or country affecting another. The problem of transboundary pollution develops through flowing air or water and is solved by international co-operation.

Examples of Environment Canada’s Transport Research:

  • Several projects study the transport of chemicals from their points of use in temperate and tropical climates to the North. These studies incorporate pesticides, polychlorinated biphenyls, polychlorinated naphthalenes, polycyclic aromatic hydrocarbons, mercury and particulate matter, among other chemicals.
  • Other researchers investigate the transport of ozone, oxidants, acid aerosols and other components of smog from Canadian and American urban/industrial locations to Canadian rural areas.
  • Studies of chemical transport in clouds frequently use research aircraft.


Chemicals in the environment do not exist in isolation, but in complex, ever-changing mixtures. Consequently, chemicals that are released into the atmosphere are often transformed into other compounds by reacting with oxygen, water or other chemicals in the air. Many reactions are enhanced by energy from the sun, and therefore vary with season, time of day and climate.

Examples of Environment Canada’s Transformation Research:

  • Most Environment Canada air quality scientists working on processes research deal with the transformation of chemicals in some way. Because the air contains extremely reactive compounds such as ozone and the hydroxyl radical, many airborne compounds undergo a complex series of reactions or transformations.
  • Several scientists are investigating how these transformations take place in smog and mixtures of oxidants.
  • Studies are also conducted on the eventual transformation of relatively unreactive chemicals, such as polychlorinated biphenyls and some pesticides.
  • Research, including field, laboratory and sealed reaction chamber studies, are carried out to better understand transformations in air that can produce compounds more toxic than the parent chemicals from which they were generated.

Levels of Chemicals in Air

All of these processes combine to produce concentrations of chemicals in the atmosphere which change over space and time.

Examples of Environment Canada’s Concentrations Research:

  • Measuring the environmental concentrations of particles and ozone to determine how concentrations of chemicals are changing over time at a high elevation site.
  • Measuring concentrations of persistent chemicals in air and precipitation in the Great Lakes region.


The removal of chemicals from the air to land and water surfaces can occur due to wet deposition where rain or snow washes out the chemical, or by dry deposition which occurs when particles settle out of air or gases adsorb to surfaces. The process of deposition returns chemicals to the water and land where they can be stored or returned to the atmosphere by evaporation or gas exchange, continuing the cycling of pollutants through the environment.

Examples of Environment Canada Deposition Research:

  • Measuring the deposition of chemicals from the atmosphere at the Borden Forest Research Station. Researchers determine how deposited chemicals move through a forest canopy, and collect data on many relevant parameters.
  • Investigations on the movement of particulate matter and the process by which airborne chemicals enter other environmental media such as soil and bodies of water.

Another process called global distillation carries chemicals from tropical and temperate regions where they are produced and used, to the colder regions at the Earth's poles. This process occurs when compounds that can be both in the gas phase and adsorbed to particles or water at ambient temperatures evaporate in warm climates and are moved by winds to colder climates where they condense and are deposited. These chemicals include some pesticides, products of combustion and polychlorinated biphenyls, some of which can accumulate in the bodies of Northern people and biota. The process is pictured below for organochlorine compounds.

Image of a globe showing the movement of chemicals from the tropics to the poles.
Movement of chemicals (organochlorines) from the tropics to the polar region through the atmosphere.
Image of organochlorine chemicals moving through the atmosphere.

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