Air Quality Monitoring and Reporting in Ontario – Fostering a False Sense of Security

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It is indisputable that poor air quality is a threat to human health, the environment and the economy. In Ontario, air pollution has been described as a public health crisis, linked to an estimated 9,500 premature deaths each year. Air pollutants also contaminate soil and water resources, damage vegetation and wildlife, and disrupt ecosystem functions. Every year, the environmental and health damages associated with air pollution cost the Ontario economy billions of dollars.

The Ontario Ministry of the Environment (MOE) monitors and provides regular updates on regional ambient air quality through its on-line Air Quality Index (AQI). These air quality updates and smog alerts are also reported by local radio and television stations. Many Ontarians rely on the AQI to make decisions about their daily activities, including whether to exercise outdoors or take other health precautions.

But do regional air quality reports really tell us everything we need to know to make such decisions? Within a monitoring region, pollutant concentrations may vary due to local influences, such as the placement of industrial facilities and major roadways. In urban centres, pollutant concentrations increase along busy streets, particularly during peak hours of traffic congestion. In short, the air that Ontarians actually breathe at street-level can differ significantly from the ambient air upon which AQI reports are based.

To better understand the various factors at play, the ECO undertook a study of the adequacy of Ontario’s air quality monitoring and reporting regime.


Air Quality Monitoring in Ontario

The Air Quality Index

MOE operates a network of 40 air quality monitoring stations that continually measure air pollutant concentrations in rural and urban locations across the province. The monitoring stations measure six key air pollutants known to be harmful to human health and the environment, namely ground-level ozone, fine particulate matter (PM2.5), sulphur dioxide, nitrogen dioxide, total reduced sulphur compounds, and carbon monoxide.

Using hourly air pollutant concentration data obtained from its monitoring stations, MOE assigns a numerical rating – known as the Air Quality Index (AQI) – to each pollutant using a common scale, or index. Based on the pollutant with the highest AQI (usually ground-level ozone or PM2.5), air quality is classified into one of five categories: very good, good, moderate, poor or very poor.

MOE reports this information to the public on the Air Quality Ontario website ( in two ways: a real-time hourly AQI rating for each monitoring station and a three-day air quality forecast, also for each monitoring station.

In addition, MOE issues smog alerts when the AQI is expected to be poor, or when persistent, widespread poor AQI readings occur.

No Information about Air Quality at Street-level

Within an airshed, pollutant concentrations can vary greatly from one particular location, or “micro-environment,” to another. Air quality measured near point sources of emissions (e.g., industrial facilities, power plants, etc.) may be far inferior to ambient air quality. Pollutant concentrations at roadways may be 60 to 80 per cent higher than concentrations only 100 metres from the road. In cities, streets densely lined with tall buildings that trap emissions, dubbed “urban canyons,” are hotspots for high levels of air pollutants. Air quality can vary even from one street to another, depending on local conditions and traffic patterns.

MOE’s air quality monitoring stations are intentionally located away from local sources of pollutants in order to provide representative information about regional average exposure to air pollutants. While this information is useful for predicting air quality on a regional scale – particularly smog events – the data reveals little about air quality in micro-environments within the monitoring region.

Growing concerns about air pollution have prompted some Ontario municipalities to study air quality at a more local scale. Mobile monitoring equipment is used to obtain detailed information about pollutant concentrations near sources of industrial and transportation-related emissions. Such information can provide valuable input into municipal transportation and planning policies that, in turn, can have a significant impact on local air quality.

In the summer of 2007, the ECO asked air quality experts to undertake some short-term, street-level monitoring of particulate matter at a variety of locations across Ontario. The monitoring results showed consistently higher PM2.5 levels at the sampling locations than at MOE’s nearest AQI monitoring stations. For example, street- level samples collected in downtown Toronto recorded concentrations of PM2.5, equivalent to an AQI in the “very poor” category. By contrast, MOE’s Toronto downtown AQI station reported air quality to be “good” at that time. The limited data collected supports the ECO’s concerns that Ontario’s current air quality monitoring regime is falling short in providing reliable information on which to make informed decisions about personal health protection.

No Consideration of Cumulative Effects

Another shortcoming of the AQI is that it does not consider the potential cumulative or synergistic effects of different pollutants present in the air at the same time. The AQI assesses each pollutant independently, and hourly AQI ratings are based solely on the pollutant with the highest rating during that time. Since every breath we take contains a combination of the pollutants present in the air around us, assessing and reporting on air quality based on one isolated pollutant does not tell the full story.

Air Quality Health Index

In addition to the AQI, in July 2007 MOE joined Environment Canada, Health Canada, Toronto Public Health and the Clean Air Partnership in a Toronto pilot project for the federal government’s new national Air Quality Health Index (AQHI). The AQHI rates the level of health risk presented by current air quality conditions on a scale of one to ten. The AQHI was designed to help the public “plan a healthy day” by making decisions based on the AQHI rating. Like Ontario’s AQI, the AQHI is based on regional air quality data; however, unlike Ontario’s AQI, it does consider the effects of a combination of pollutants (ozone, particulate matter and nitrogen dioxide) rather than one individual pollutant.

Learning from Others

While Ontario’s AQI program is similar to programs used elsewhere in North America, air quality monitoring and forecasting systems operating in some European cities are considerably more sophisticated. Cities such as London, Paris, Vienna and Copenhagen use large, city-wide monitoring networks to obtain real-time information about air quality, not only at regional background levels, but at the street-level as well.

For example, air quality information collected from over 200 continuous monitoring stations across the Greater London Area is used to map real-time data about local air quality. Street-level air quality forecasts are also provided, using data on local traffic patterns, weather forecasts and regional atmospheric composition. The public has access to detailed maps and descriptions of real-time and predicted air quality in specific locations, at a resolution fine enough to observe air quality patterns on a street-by-street basis.

The Risks of Inadequate Monitoring

Ontario’s lack of local air quality data not only creates gaps in the information conveyed to the public; it may also beget inadequate regulatory responses to signifcant air quality issues. For example, relatively little regulatory attention has been paid to traffic-related air pollution, a local air quality issue in urban centres. While MOE has established some regulated programs, such as Drive Clean, to reduce vehicle emissions, vehicles remain the largest single domestic source of some smog- causing pollutants.

Similarly, MOE may not have sufficient local air quality data to develop Certificates of Approval (Cs of A) for industrial facilities that are appropriately protective of air quality in surrounding communities. Relatively high concentrations of air emissions from industrial facilities are permitted on the presumption that pollutant concentrations dilute as they move away from the stack. However, Cs of A for industrial facilities are not required to take into account potential cumulative effects of pol- lutant concentrations from other sources, leading to local loadings of pollutants that could far exceed safe or acceptable ambient levels.

The ECO has previously expressed disappointment that, despite a recent overhaul of the regulatory framework for controlling industrial air emissions, cumulative effects assessments are not required as part of the C of A (Air) review process. Such assessments are critical to predicting the future state of air quality in local and regional airsheds. This concern was raised in 2006 in an application for review of the C of A (Air) for the Portlands Energy Centre, an electrical generating station under construction on the eastern lakeshore of the City of Toronto (described in Ontario's Electricity System in our 2006–2007 Annual Report) . The issue arose again in the discussion of an application for review of Cs of A (Air) for the ArcelorMittal Dofasco Inc. facility in Hamilton (see Dofasco KOBM Meltshop).

ECO Comment

The ECO is concerned that Ontarians who rely on the AQI may be lulled into a false sense of security about the quality of the air that they encounter as they go about their daily activities. While encouraging the public to take health precautions on smog days is laudable, it implies that precautions are not necessary on other days. This is reinforced by the language used to describe air quality on non-smog days (i.e., “very good,” “good,” and even “moderate”), and does not reffect the fact that inferior air quality (and accompanying health risks) may be encountered at street-level even when the AQI is favourable. In effect, the current system may be inadvertently enticing people to expose themselves to inferior air quality, under the false impression that a favourable AQI means the air at street-level is safe to breathe.

The ECO sees a pressing need to overhaul Ontario’s outdated and inadequate air quality monitoring and reporting regime. Although improvements have been made since the AQI was introduced in 1988, it falls far short of its potential. Ontarians should have access to complete information about local air quality in order to make informed decisions about their daily activities and to take necessary health precautions. The current regime simply does not have the resolution required to adequately measure or predict air quality impacts related to major traffic corridors or important point sources.

The ECO urges MOE to build on its existing air quality monitoring network to equip Ontarians with comprehensive information about the quality of the air where we breathe it: at street-level. A key component of such a system would be a public education and awareness program, and enhanced tools for communicating air quality information to the public. Ontario could draw on the experiences of European cities, and coordinate with other existing initiatives, to develop a world-class air quality monitoring and reporting system that will instill confidence in the Ontario public.

But improvements should not stop there; information about local air quality is also critical input to the larger air regulatory framework and can be used to support other provincial and municipal programs, particularly those relating to transportation and land use planning. There needs to be a shift in our thinking: air quality at a micro-environment scale must be factored into the equation. Integrating an enhanced air quality monitoring and reporting regime with Ontario’s existing air regulatory framework could be a first step.

Finally, the ECO commends MOE for using the AQI to encourage Ontarians to reduce emissions during smog events. The ECO urges the government to consider all potential tools for improving air quality, including exploring the merits of fuel alternatives, designating low emission zones, enhancing public transit, continuing to update air standards, and updating old Cs of A (Air) to current standards, to name just a few.

Recommendation 3:

The ECO recommends that MOE expand its air quality monitoring and reporting program to include a network of street-level monitoring stations.

This is an article from the 2007/08 Annual Report to the Legislature from the Environmental Commissioner of Ontario.

Citing This Article:
Environmental Commissioner of Ontario. 2008. "Air Quality Monitoring and Reporting in Ontario - Fostering a False Sense of Security." Getting to K(No)w, ECO Annual Report, 2007-08. Toronto, ON : Environmental Commissioner of Ontario. 57-62.

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