Atmospheric Processes

[Figure adapted from Schroeder and Lane, 1988.]

ARQP scientists study the processes which govern how chemicals enter, move through, and exit from the atmospheric environment. Our research falls into the categories of emission, transport, transformation, concentrations of chemicals in air and deposition.

Emission

Chemicals enter the air from human 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 waters and soils and later released to the atmosphere.

ARQP Emission Research:

In one emissions project, scientists collect particulate matter in air and trace it to its source in a process called source apportionment. Other researchers use lidar and research aircraft to directly test industrial emission plumes. Another project studies natural or recycled mercury emissions from soils. Scientists are also collecting air samples at various heights over corn fields in the southern Unites States to measure the rate at which pesticides are released from the soil.

TRANSPORT

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

ARQP 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, PCBs, PCNs, PAH, 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. Another project used lidar to study global particulate matter transport from the space shuttle Columbia.

Transformation

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.

ARQP Transformation Research:

Most ARQP scientists 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. In contrast, the eventual transformation of relatively unreactive chemicals, such as PCBs and some pesticides, interests scientists as well. Because transformations in air can produce compounds more toxic than the parent chemicals from which they were generated, scientists are working to understand transformation in the field, the laboratory, and in a sealed reaction chamber.

Environmental Concentrations

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

ARQP concentrations Research:

Virtually all of the ARQP scientists monitor the environmental concentrations of contaminants. A program of measurement is a useful tool for determining how concentrations of chemicals are changing over time and space and in response to different human activities or environmental occurrences. The Centre for Atmospheric Research Experiments (CARE), north of Toronto, Ontario, Canada, is a rural research station used to monitor background concentrations of chemicals in air. Two monitoring programs, the Canadian Atmospheric Mercury Measurement Network (CAMNet) and the Integrated Atmospheric Deposition Network (IADN) monitor concentrations in air nationally and in the Great Lakes region, respectively. Other scientists operate an atmospheric oxidant measurement program at two remote sites: atop Mt. Sutton in Quebec and at Alert, Nunavut.

ARQP Scientists and Concentrations Research

Deposition

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. 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.

ARQP Deposition Research:

Two facilities used to monitor the deposition of chemicals from the atmosphere are the Forest Flux Research Station and a research buoy on Lake Ontario. Researchers at the forest flux station measure how deposited chemicals move through a forest canopy, and collect data on many relevant parameters. The buoy has been used to monitor the movement, or flux, of chemicals between the air and the surface of Lake Ontario. Other deposition projects investigate the movement of particulate matter and the process by which airborne chemicals enter other environmental media such as soil and bodies of water.

Global Distillation

Another process called global distillation, or the grasshopper effect, 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 semivolatile compounds (those that are both gases and liquids at ambient temperatures) evaporate in warm climates and are moved by winds to colder climates where they condense and are deposited. Semivolatile chemicals include some pesticides, products of combustion and PCBs, some of which can accumulate in the bodies of Northern people and biota as a result of this process. The process is pictured below for organochlorine compounds.

Global distillation