Glossary of Terms Related to Air Quality Management

Abatement     Reducing the degree or intensity of pollution.

Aerosol           Suspensions of tiny liquid and/or solid particles in the air.

Air Contaminant        Any particulate matter, gas or combination of these other than water vapour. (See: air pollutant.)

Air Quality Health Index (AQHI)       The Air Quality Health Index (AQHI) is a new, national health initiative that provides current hourly air quality readings and related health messages.

Air Pollutant  Any substance in air that could, in high enough concentrations, harm people, other animals, vegetation, or material.

Pollutants may include almost any natural or artificial composition of airborne matter capable of being airborne. They may be in the form of solid particles, liquid droplets, gases, or in combination of these.

Generally, they fall into two main groups: (1) those emitted directly from identifiable sources and (2) those produced in the air by interaction between two or more primary pollutants, or by reaction with normal atmospheric constituents, with or without photoactivation.

Air pollutants are often grouped in categories for ease in classification; some of the categories are: solids, sulfur compounds, volatile organic chemicals, particulate matter, nitrogen compounds, oxygen compounds, halogen compounds, radioactive compound, and odours. Common examples of pollutants include: dust, wood smoke, nitrogen dioxide, ground-level ozone, and particulate matter.

Air Pollution Episode   A period of abnormally high concentration of air pollutants which can cause illness and death. High concentrations are often due to low wind speeds and temperature inversion. (See: episode, pollution.)

Air  Quality  Index (AQI)        An  AQI  is  a  way  of  transforming  complex  air  quality measurements into a single number or descriptive term. It describes the measured air quality  and  the  publicly  perceived  air  quality  at  any  given  time.  The AQI in BC is read as:

0 to 25 –  GOOD
26 to 50 –  FAIR
51 to 100 –  POOR
100+  – VERY POOR

An AQI in excess of 50 represents the point at which BC Environment normally becomes concerned about the level of human health impact. The British Columbia AQI is directly comparable  to  the  AQI’s  issued  in  all  major  Canadian  cities  as  it  follows  the  same Federal guidelines.

Air Quality Management      Administrative activities carried out to implement an air quality management plan, including amendment of permits for industrial and other point contaminant sources, establishment of by-laws and other local and regional regulatory controls on mobile and area contaminant sources, and public education on ways to reduce and eliminate use of air contaminants in everyday activities.

Air Quality Management Plan (AQMP)       A blueprint for managing community development and for controlling air contaminant sources so as to improve or maintain air quality for the protection of human health and the environment in an airshed.

Airborne Particulates                        Total suspended particulate matter found in the atmosphere as solid particles or liquid droplets.  The chemical composition of particulates varies widely, depending on location and time of year. Sources of airborne particulates include: dust, emissions from industrial processes, combustion products from the burning of wood and coal, combustion products associated with motor vehicle or non-road engine exhausts, and reactions to gases in the atmosphere.

Airshed           Topography (hills and valleys) and weather conditions can interact to prevent the mixing and exchange of air from inside and outside a given area. This area is called an “airshed.” A good example of an airshed is a valley where the surrounding mountains act as a physical barrier to air moving out of the valley when the air is still. Because weather and wind conditions change from day to day, the boundary of an airshed isn’t constant; it can change with the weather.

Ambient air quality   Ambient air quality describes the level of air pollutants in a particular region. Poor ambient air quality means pollutant levels are high enough to cause concerns. Ambient air quality is measured near ground level, away from direct sources of pollution.

Ammonia (NH3)          A compound containing nitrogen and hydrogen, and known for a sharp, pungent smell. It is emitted mostly from agricultural and animal husbandry activities.  Other sources of ammonia are fuel and waste combustion, chemical industry and refrigeration facilities. It contributes to the formation of inhalable particulates and visibility-reducing particles.

Area Source   Any source of air pollution that is released over a relatively small area but which cannot be classified as a point source. Such sources may include vehicles and other small engines, small businesses and household activities, or biogenic sources such as a forest that releases hydrocarbons.

Carbon Monoxide (CO)         A colorless, odourless, poisonous gas produced by incomplete fossil fuel combustion.

Carbon Dioxide (CO2)             A colourless, odourless, non-combustible gas. CO2 is a normal constituent of air. This gas is formed by certain natural processes, the burning of fuels and wastes containing carbon, and heating of minerals or products containing carbonate.

Cogeneration             The consecutive generation of useful thermal and electric energy from the same fuel source.

Concentration                        The amount of a pollutant in the air at a given location, expressed as the weight of volume of pollutant per volume of air, such as parts per billion (ppb) or micrograms per cubic metre of air (µg/m3).

Common air contaminants (CACs)   CO, VOCs, NH3, NOx, SOx and PM

Ecosystem      The interacting system of a biological community and its non-living environmental surroundings.

Emission         Pollution discharged into the atmosphere from smokestacks, other vents, and surface areas of commercial or industrial facilities; from residential chimneys; and from motor vehicle, locomotive, or aircraft exhausts.

Emission Inventory    A listing by source of the amount of air pollutants discharged into the atmosphere of a community; used to establish emission standards.

Emission Standard     The maximum amount of contaminant discharge legally allowed from a single source, mobile or stationary.

Episode (Pollution)    An air pollution incident in a given area caused by a concentration of atmospheric pollutants under meteorological conditions that may result in a significant increase in illnesses or deaths.

Exposure         A combination of the level of a pollutant and the amount of time a person spends in the presence of a pollutant. Exposure determines the level of risk associated with different types of pollutants.

Fine particulates        Particulate matter with an aerodynamic diameter of 2.5 microns or less (PM2.5). Ambient fine particulate matter consists basically of five species: sulphates, ammonium nitrate, organics, elemental carbon, and soil dust.

Fugitive Dust                A particulate emission made airborne by forces of wind or people’s activities. Unpaved roads, construction sites, and tilled land are examples of areas that originate fugitive dust.

Fugitive Emissions     Emissions not caught by a capture system.

Fume               Tiny particles trapped in vapour in a gas stream.

Greenhouse Gas (GHG)          A gas that, when in equilibrium, keeps our planet at a livable temperature by trapping heat from the sun, but not too much heat.

Since the industrial revolution a rapid increase in GHGs in the atmosphere is believed to be contributing to global climate change. The major GHGs are carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O).

Ground Level Ozone              Ozone is a gas that can be “good” or “bad” for your health and the environment, depending on its location in the atmosphere. The layer of air closest to the Earth’s surface is the troposphere. Here, ground level or “bad” ozone is an air pollutant that is harmful to breathe and it damages crops, trees and other vegetation. Ground level ozone is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. Emissions from industrial facilities, utilities that burn fossil fuels, motor vehicle exhaust, gasoline vapours, and chemical solvents are some of the major sources of NOx and VOCs.

Hydrocarbons                        Hydrocarbons refer to the most important class of organic compounds. Hydrocarbons contain only the elements hydrogen and carbon. They occur in petroleum and natural gas. Commercial petroleum products such as gasoline, kerosene, airplane fuel, lubricating oils, and paraffin wax are mixtures of hydrocarbons.

Inhalable Particles     All dust capable of entering the human respiratory tract – typically refers to PM10.

Inversion (a.k.a. Temperature Inversion)    Typically air layers become cooler with elevation allowing warm air to rise out of valleys and disperse. An inversion occurs when a layer of warm air prevents the rise of cooler air below and traps pollutants beneath it. An inversion can lead to an air pollution episode.

Irritant                        A substance that can cause irritation of the skin, eyes, or respiratory system. Effects may be acute from a single high-level exposure, or chronic from repeated low-level exposures to such compounds as chlorine, nitrogen dioxide, and nitric acid.

Microgram (µg or mcg)         A metric unit of mass equal to 0.001 milligram (mg) or one millionth of a gram. The ratio of 1 µg/m3 is similar to a grain of sand suspended in a small apartment.

Micron            A unit of length equal to one millionth of a meter; the unit of measure for wavelength.

Mitigation      Measures taken to reduce adverse impacts on the environment.

Mobile Source                       Any non-stationary source of air pollution such as cars, trucks, motorcycles, buses, airplanes, and locomotives.

Monitoring     Periodic or continuous surveillance or testing to determine the level of pollutant levels in various media or in humans, plants and animals.

NH3      Ammonia, see entry for Ammonia

Nitrogen         Nitrogen gas (N2) makes up 78.1% of the Earth’s air, by volume.  All organisms must have nitrogen to live. Nitrogen makes up an important part of protein molecules, which are found in protoplasm. Protoplasm is the living material in all plant and animal tissues. Human beings and animals get protein by eating plants and animals.

Most plants must manufacture protein from simple nitrogen compounds dissolved in the soil. Some of this dissolved nitrogen comes from the atmosphere in the form of nitric acid (HNO3). Lightning causes nitrogen and oxygen in the air to form compounds called nitrogen oxides. These oxides react with water to form nitric acid, which is carried to the earth dissolved in rainwater.

Nitrogen dioxide (NO2)         A gas consisting of one nitrogen and two oxygen atoms. It absorbs blue light and therefore has a reddish-brown color associated with it.

Nitric oxide (NO)       Formed as a by-product in the combustion of gasoline in automobile engines. Sunlight causes the nitric oxide in the lower atmosphere to react with oxygen to form ozone, which can be a harmful pollutant at ground level.

Nitrogen Oxides (NOx)          Term used to describe the sum of nitric oxide (NO), nitric dioxide (NO2), and other oxides of nitrogen, which plays a major role in the formation of ozone. The major sources of man-made NOx emissions are high temperature combustion processes, such as those occurring in automobiles and power plants.

Non-Point Sources    These are a variety of pollution sources that are difficult or too small to measure on an individual basis. There are far too many cars, fireplaces, and lawnmowers to track exactly how much each one is emitting by itself, but they can all add up to a significant amount of total emissions. Therefore, for the purpose of developing an emission inventory, these sources are combined into categories called “non-point” or “area” sources.

Non-Road Emissions              Pollutants emitted by combustion engines on farm and construction equipment, gasoline-powered lawn and garden equipment, and powerboats and outboard motors.

Open Burning                        The combustion of material with or without control of the combustion air and without a stack or chimney to vent the emitted products of combustion to the atmosphere, such as slash burning or bon fires.

Outdoor Wood-fired Hydronic Heaters (OWHH)   Also known as an “Outdoor Wood Heater,” “Outdoor Wood Boiler,” or “Outdoor Wood Furnace”, these units burn wood to heat water that is piped underground to a nearby structure (usually a home) resulting in heat for the building. An OWHH resembles a small shed with a smokestack, typically located on the outside of the building to be heated. Outdoor wood-fired hydronic heaters can be substantially dirtier and less efficient than most other home heating technologies. With their smouldering fires and short smokestacks (usually no more than six to ten feet tall), OWHHs can create heavy smoke and release it close to the ground, where it may linger and expose people in the area to nuisance conditions and health risks.

Oxygen (O2)    Humans and the other animals obtain oxygen from the air, filtered into the bloodstream through the lungs. Blood then carries oxygen to the cells of the body, where it combines with other chemicals obtained from food to produce energy and to perform the functions of the individual cells. Carbon dioxide is produced in the cells as a waste product and is expelled from the body through the respiratory system.  PM2.5 pollution deposits itself right alongside the O2 molecules in the alveoli of the lungs, obstructing the absorption of O2 with the smallest components of PM2.5 being absorbed into the bloodstream.

Ozone (O3)      A gas found in two layers of the atmosphere, the stratosphere and the troposphere. In the stratosphere (the atmospheric layer 7 to 10 miles or more above the earth’s surface) ozone is a natural form of oxygen that provides a protective layer shielding the earth from ultraviolet radiation. In the troposphere (the layer extending up 7 to 10 miles from the earth’s surface), ozone is a chemical oxidant and major component of photochemical smog. Ozone in the troposphere is produced through complex chemical reactions of nitrogen oxides, which are among the primary pollutants emitted by combustion sources; hydrocarbons, released into the atmosphere through the combustion, handling and processing of petroleum products; and sunlight.

PM (Particulate Matter)       PM is microscopic particles in the air. These particles, capable of being inhaled by humans, are divided into two size ranges: PM2.5 and PM10. Between the two, “fine” particles less than 2.5 micrometers in size (PM2.5) are responsible for causing the greatest harm to human health.

PM10                    Particles in the atmosphere with a diameter of less than or equal to a nominal 10 micrometers. Otherwise known as inhalable particulates and/or coarse fraction particulates.

PM2.5               Particles in the atmosphere with a diameter of less than or equal to a nominal 2.5 micrometers. Otherwise known as respirable particulates and/or fine fraction particulates.

Point Source              A stationary location or fixed facility from which pollutants are discharged; any single identifiable source of pollution; e.g. a pipe, ditch, ship, ore pit, factory smokestack. A point source is easy to regulate using an emission permit process.

Pollutant        Generally, any substance introduced into the environment that adversely affects the health of humans, animals or ecosystems.

Pollution        Generally, the presence of a substance in the environment that because of its chemical composition or quantity prevents the functioning of natural processes and produces undesirable environmental and health effects.

Precautionary Principle        In situations where there is a reasonable expectation of harm, the precautionary principle us used to base decision on avoiding or reducing unnecessary health or environmental risks even when scientific information is lacking.


Prescribed Burning    Controlled application of fire to wild land fuels in either their natural or modified state. Under specified environmental conditions this allows the fire to be confined to a predetermined area, and produce the fire behaviour and fire characteristics required to attain planned fire treatment and resource management objectives. Since fire is a natural ecosystem process, prescribed burning can be used to diversify native flora and fauna in areas where fire has been suppressed for periods of time. It is also used to protect structures and communities from wildfire by reducing the amount of fuel available in adjacent forests.

Risk Assessment         Qualitative and quantitative evaluation of the risk posed to human health and/or the environment by the actual or potential presence and/or use of specific pollutants.

Smart Growth                        An initiative or plan that intends to improve ways in which human settlement occurs for the purpose of reducing impacts on the environment, as well as to improve quality of life. Smart Growth initiatives are attempting to address urban sprawl; motor vehicle use; environmental integrity and food-system security; and affordable housing, among many other topics.

Smog               Smog usually is produced through a complex set of photochemical reactions involving volatile organic compounds (VOC’s) and nitrogen oxides in the presence of sunlight that result in the production of ozone. Smog-forming pollutants come from many sources, such as automobile exhausts, power plants, factories, and many consumer products.  In typical urban areas, at least half of the smog precursors come from cars, buses, trucks, and boats.

Smoke Control Forecast        Designed to predict the capability of the atmosphere to effectively disperse pollutants such as small particulate matter (smoke).

Smoke Dispersion Factors      Two factors control the spread or dispersion of small particles or gases. These factors are the wind speed (controls horizontal spread) and the height of the “mixed layer”. The mixed layer is the portion of the atmosphere from the ground up to the level at which gases and small particles freely mix. For example, smoke from a smokestack will tend to rise to the top of the mixed layer and then level off.

Sulphur Dioxide (SO2)           Sulphur Dioxide is a colorless, poisonous gas with a sharp odour. Sulphur dioxide forms naturally from volcanic activity and from the decay of organic matter. It can be manufactured by burning sulphur dioxide or heating metallic sulphur compounds. Sulphur dioxide is also released into the atmosphere by oil refineries and by factories and electric power plants that burn coal or oil.

In the air people breathe, sulphur dioxide can irritate the eyes and respiratory system. It will also dissolve in water droplets to form acid rain, which can harm or even kill plants and wildlife and damage buildings. Acid rain also may form when sulphur dioxide in the air is converted into sulphur trioxide.

Sulphur Oxides (SOx)                         Oxides of sulphur, mostly sulphur dioxide (SO2)

Ventilation Index        The ventilation index is formed by multiplying the mixed layer height by the average wind speed in this mixed layer. Stronger wind speeds and thicker mixed layers will produce higher ventilation index values. For convenience, the actual numbers are converted to a scale of 0 to 100. A ventilation index of ’0’ implies no ability of the atmosphere to disperse pollutants while a value of ‘100’ implies an excellent ability to disperse pollutants.

The ventilation index in British Columbia is divided into the following categories:

0 – 33 = POOR             Open burning is not acceptable (or permitted by some by-laws)

34 – 54 = FAIR             Open burning is not acceptable

55 – 100 = GOOD        Conditions are acceptable for burning

For most locations, ventilation index values are poor from sunset until late morning. For locations within valleys, the ventilation index should be lowered if the mixing height is less than the height of the surrounding hills.

Volatile Organic Compound (VOC)   Any organic compound that participates in atmospheric photochemical reactions.

Wood-Burning Stove Pollution       Air pollution caused by emissions of particulate matter, carbon monoxide, total suspended particulates, and polycyclic organic matter from wood-burning stoves.