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Air Quality Forecasts: The Science-Behind-the-Scenes

By:  Silvina Carou (S&T Liaison)

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The Problem 

Smog, the hazy noxious mix of air pollutants hanging over many communities in Canada, can contribute to heart and respiratory problems, sometimes leading to premature death.

Skyline of Montreal showing smog | Photo:  photos.comSmog’s main components are particulate matter (PM) and ground-level ozone. PM and gases such as SO2, NOx, VOC and NH3 are emitted into the air from natural and man-made sources. Sources include combustion of fossil fuels (e.g., vehicles, electricity generation, metal smelting), mechanical generation of dust from soil and roads, oceans (salt) and vegetation (VOC, bio-aerosols). Under the right conditions - such as high pollutant concentrations, warm temperatures, humidity and sunlight - these gases and particles react with each other to produce ozone and fine PM (<2.5 µm in diameter). Wind also influences concentrations of air pollutants either by trapping them in one location (stagnant conditions), or by carrying them hundreds of kilometres away from their source to other areas in Canada and the U.S.

Unlike the ozone in the upper atmosphere that protects the planet from UV radiation, ozone at ground level worsens air quality.

Smaller particles are of greatest concern because they remain suspended in the atmosphere longer and can penetrate more deeply into the lungs. Smog is responsible for 9500 premature deaths per year across Ontario (not just in cities or industrial centres), with 1000 occurring during or immediately after periods of increased pollution and the rest likely due to long-term exposure to air pollutants (Ontario Medical Association, 2008). Children, the elderly, asthmatics and people suffering from cardio-respiratory disease are particularly susceptible. Smog also reduces visibility, damages crops, and increases vulnerability to disease for some tree species.

Seeking Solutions through S&T

Environment Canada works with Health Canada and provincial, territorial and municipal governments to inform Canadians about current and future poor air quality conditions and assist them to minimize potential health impacts. This service would not be possible without the science-behind-the-scenes that measures and predicts levels of pollutants in the air.

Environment Canada’s air quality and weather experts generate air quality forecasts using a numerical air quality model, in much the same fashion as weather forecasts are produced. The air quality model simulates the emission, dispersion, physical-chemical processing, transport and deposition of pollutants in the atmosphere. Developing such models has involved decades of research and analysis of observational data.

Using emissions data for PM and smog-producing gases from both Canada and the U.S., the air quality forecast model computes the expected atmospheric concentrations of PM and ozone for the next two days on Environment Canada’s supercomputer in Montréal. This forecast is then checked by weather forecasters with regional expertise and adjusted, if need be, with knowledge derived from the latest observations of weather and air quality.

Tree with smog in background | Photo:  photos.comCurrent air quality conditions are also tracked and reported based on measurements taken by the National Air Pollution Surveillance Network (a federal-provincial-municipal co-operative program), the Canadian Air and Precipitation Monitoring Network (CAPMoN) and at provincial sites. New techniques that use near-real-time data from these networks as well as those from satellite-based instruments are being developed to provide a better definition of current conditions, which the air quality forecast model will use to improve the quality and accuracy of the forecasts.

Transforming Knowledge into Action

Who can use these results?

Current air quality conditions, forecasts and advisories are available to Canadians in all ten provinces. Environment Canada also produces ventilation forecasts for some communities in the Arctic. Air Quality Advisories are issued when either ground-level ozone or fine PM falls into the poor air quality category: that is, when air pollutant levels exceed national standards.

In June 2000, federal and provincial/territorial environment ministers agreed on Canada-wide Standards (CWS) for particulate matter (PM2.5) and ground-levelozone to be achieved by 2010 to address the health and environmental impacts of these substances.

Until now, air quality has been reported using an Air Quality Index (AQI) that ranges from 0–25 (Good), 26–50 (Fair), 51–100 (Poor) to greater than 100 (Very Poor). Although various air pollutants are analyzed and reported, AQI readings reflect the highest measured pollutant or that predicted to be highest within a given hour. Generally speaking, ozone tends to be the dominant pollutant in the summer months, due to weather conditions, while PM dominates in the winter months.

While the AQI is still in use, several communities across Canada are testing a new and improved index called the Air Quality Health Index (AQHI) that was developed by Environment Canada and Health Canada in partnership with a number of government and non-government stakeholders. The AQHI improves on the AQI by accounting for the health risks associated with the “mix” of three common pollutants (ozone,PM2.5/PM10 and NO2 ), rather than a single pollutant. It also expresses air quality conditions on a scale linked to health risk categories: 1–3 (Low health risk), 4–6 (Moderate health risk), 7–10 (High health risk), 10+ (Very high health risk). Health messages associated with each risk category are customized for the general and the “at risk” population.

Example of forecast average (6-hour) PM2.5 levels (at 10 m height) over North America (July 2008).  Source:  www.weatheroffice.gc.caAir quality models are used for more than just forecasting future air quality conditions. By putting different possible weather conditions and air pollutant levels into the models, we can do “what if” scenarios that help determine the effectiveness of current and suggested domestic and international air quality policies aimed at improving air quality in Canada.

Similarly, scenarios help determine the most suitable and effective mix of air pollution emissions reductions that will result in maximum benefits to Canadians and their environment. For instance, past trends and predictions of air quality conditions based on different emission reduction scenarios formed the scientific basis for the Canada-U.S. Air Quality Agreement and have also been key to the development of Canada’s Clean Air Regulatory Agenda.

Benefits to Canadians

Heart and respiratory problems can lead to absenteeism from school and work, more hospital admissions, and premature death. Air quality forecasts and tools like the AQHI enable Canadians to plan and minimize impacts on their health and the environment. 

Although there are high costs to cutting down on air pollution, significant economic benefits come from reducing human and ecosystem exposure to it. Reductions in illness and mortality have direct social benefits through decreased health care costs and improved work-place productivity. Preventing further environmental damage as a result of air pollution also benefits forest, agricultural, fish and tourism productivity, all essential industries to Canada.  

Health Canada estimates that a 3% reduction in summertime ground-level ozone levels, combined with an 8% reduction in PM levels would result in approximately 1200 fewer deaths, hundreds of fewer hospital admissions and emergency department visits, and tens of thousands of fewer episodes of asthma and other respiratory symptoms, with social welfare benefits greater than $6 billion (Canada, 2007).

Environment Canada estimates that the ozone component of smog could be costing the agricultural industry over $500 million in lost revenue every year and that poor visibility induced by smog costs the tourist industry in areas like Vancouver up to $7.45 million in lost future revenue per extreme episode (McNeill and Roberge, 2000).

For more information:

Air Quality Health Index

Air Quality Health Index - Weather Office

Air Quality Services

Canada-wide Standards for Particulate Matter (PM) and Ozone

Clean Air Online: Smog

Health Canada Air Quality

Key references:

Canada.  2007.  Regulatory Framework for Air Emissions

McNeill, R., and A. Roberge.  2000.  The impact of visual air quality on tourism revenues in Greater Vancouver and the Lower Fraser Valley.  Prepared for Environment Canada, Georgia Basin Ecosystem Initiative, Vancouver, B.C.

Ontario Medical Association, 2008.

S&T Liaison | Tel 905 315 5228 | Fax 905 336 4420
© Her Majesty the Queen in Right of Canada, represented by the Minister of Environment, 2008.
Catalogue No. En164-15/7-2008E-PDF; ISBN 978-1-100-10366-2