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In addition to monitoring emissions directly from their sources, air quality can also be measured by considering ambient levels. Ambient levels are the actual concentration of a pollutant in the air. They are usually reported in parts per million (ppm), parts per billion (ppb), or micrograms or nanograms per cubic metre (µg or ng/m3).
An effective monitoring program of ambient air quality measurements is important for policy and regulatory purposes, for characterizing emissions in accordance with legislation and guidelines, and to assess the impacts of air quality on human health and the environment. Since ambient air quality measurements quantify air quality impacts, they are often used in comparisons to air quality modelling results.
In Canada, ambient air quality measurements are used for a wide range of purposes such as:
- to determine as well as predict the human health and environmental impact of air pollution, such as through the Air Quality Health Index.
- to enable Canadians to understand how the air quality around them may impact their health.
- to establish a baseline for air quality and to determine long term trends, which requires comparable, high quality data from the same sites over long periods of time.
- to track progress of policy, regulatory and strategic decisions at local and national levels.
- to support the reporting of Canadian Environmental Sustainability indicators.
- to contribute data and information to science and risk assessments such as the Smog, Priority Substances List and Chemicals Management Plan assessments.
- to identify emerging air quality issues and identify contributing sources and apportion emissions by source category or by region or country.
- to validate air quality models developed by Environment Canada such as the Global Environmental Multi-scale – Modelling air quality and CHemistry (GEM-MACH) and for atmospheric processes research.
- as a basis for key national and international agreements, such as the Canada-U.S. Air Quality Agreement, Canada-Wide Standards for Particulate Matter and for Ozone.
In order to evaluate ambient air quality in Canada, Environment Canada maintains a series of monitoring stations across Canada, in both urban and rural areas as well as in some remote locations such as at Alert, Nunavut in Canada’s Arctic. These stations are being used for monitoring and surveillance of air contaminants, through programs designed to support internal regulatory policies, track actual concentration trends, permit comparisons with accepted air quality standards, and to fulfill bi-national obligations such as the Canada-U.S. Air Quality Agreement.
Environment Canada’s ambient air quality monitoring programs measure a number of target compound groups of atmospheric chemicals, including:
- Particulate Matter (total, PM10, and PM2.5)
- Sulphur dioxide and other acidic gases
- Nitrogen oxides
- Carbon monoxide
- Organic and elemental carbon
- Volatile Organic Compounds
- Polyaromatic hydrocarbons
- Anions and cations
- Metals such as lead
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