F. Gases and Atmospheric Chemistry · Gases and Atmospheric ChemistryAssessing Air Quality and Canadian Initiatives
F1.2 F1.1 A1.9 A2.1About 70 minutes
Learning goals- I can read and interpret the Air Quality Health Index.
- I can assess local air quality using data and my knowledge of pollutants.
- I can describe Canadian initiatives to reduce air pollution.
- I can evaluate how effective an initiative is, using evidence and several perspectives.
- I can explain why some communities, including some First Nations, face greater exposure to air pollution.
Words to know
Air Quality Health Index (AQHI)
A Canadian scale from 1 to 10+ that reports the health risk from ground-level ozone, PM2.5 and NO₂.
Canadian Ambient Air Quality Standards (CAAQS)
National targets for outdoor concentrations of PM2.5, ozone, SO₂ and NO₂.
temperature inversion
A layer of warm air above cooler air near the ground, which traps pollutants.
environmental justice
The fair treatment of all people in environmental decisions, so no community bears an unfair share of pollution.
carbon pricing
A policy that puts a price on CO₂ emissions to encourage lower-emission choices.
Is the air safe today?
On some summer days, a notice pops up on your phone: Special air quality statement: high levels of air pollution due to wildfire smoke. In June 2023, during Canada's record-breaking wildfire season, smoke pushed the Air Quality Health Index in Toronto and other Ontario communities into the "high risk" range, and people were advised to limit time outdoors. How is air quality measured and reported? And what have Canadians done to make the air cleaner? This lesson brings the unit together: you'll assess air quality data and evaluate Canadian initiatives.
The Air Quality Health Index (AQHI)
The AQHI was developed by Health Canada and Environment and Climate Change Canada. It is reported for communities across Ontario and much of Canada. It combines the health risks from three pollutants, measured at monitoring stations:
- ground-level ozone (O₃)
- fine particulate matter (PM2.5)
- nitrogen dioxide (NO₂)
The result is a number on a scale from 1 to 10, with "10+" for very high risk. Each level comes with health advice for the general population and for people who are more sensitive, such as people with heart or lung conditions, older adults and young children.
Reading air quality data
To assess air quality in your area, look at the AQHI over time, compare it with the weather, and think about the sources nearby. Typical patterns in Ontario:
- Ozone peaks on hot, sunny summer afternoons (lesson on the atmosphere).
- NO₂ is highest near busy roads during rush hour.
- PM2.5 rises with wood smoke in winter and with wildfire smoke in summer, and can be trapped near the ground by a temperature inversion (cool air under warm air).
- Wind direction matters: some of southern Ontario's ozone and particles blow in from the United States.
Canadian initiatives to improve air quality
1. The Canada–United States Air Quality Agreement (1991). Acid rain doesn't stop at the border. Under this agreement both countries committed to cut SO₂ and NOx emissions; an Ozone Annex added in 2000 targeted smog-forming pollutants. Combined with the smelter improvements you saw in Sudbury, SO₂ emissions in eastern Canada fell sharply and many acidified lakes have begun to recover (recovery is slow in lakes with little natural buffering).
2. Ontario's coal phase-out. Ontario replaced coal-fired power plants with nuclear, hydro, natural gas and renewable power. The last coal-fired station stopped burning coal in 2014. Together with cleaner vehicles and U.S. reductions, this made smog advisories much rarer than they were in the early 2000s.
3. Cleaner vehicles and fuels. Federal regulations set limits on vehicle exhaust (CO, NOx, hydrocarbons, particles) and on sulfur in gasoline and diesel (low sulfur protects catalytic converters). Ontario's Drive Clean emissions-testing program for passenger vehicles ran from 1999 to 2019; it was ended for cars because modern vehicles had become much cleaner, while testing of heavy-duty vehicles continued.
4. National air quality standards. The Canadian Ambient Air Quality Standards (CAAQS) set targets for PM2.5, ozone, SO₂ and NO₂ that governments use to manage air zones.
5. Carbon pricing. Pricing CO₂ emissions is meant to make low-carbon choices cheaper by comparison. Canada's consumer fuel charge was set to zero as of April 1, 2025; carbon pricing for large industrial emitters continues. Whether and how to price carbon is still debated, which makes it a good topic to evaluate with evidence.
Communities leading the way: Aamjiwnaang First Nation
Aamjiwnaang First Nation is an Anishinaabe community beside Sarnia, Ontario. The area around it, often called "Chemical Valley", contains dozens of petrochemical and industrial facilities. For many years, community members have raised concerns about the air they breathe, gathered their own observations and data, and pushed governments and companies for better monitoring and stricter rules.
In April 2024, air monitors in the community recorded very high levels of benzene (a VOC that can cause cancer), some people became ill, and Aamjiwnaang declared a state of emergency. In May 2024, Ontario's environment ministry suspended the approval of a nearby chemical plant, requiring it to stop production until it repaired leaking equipment and controlled its benzene emissions. The situation shows why where pollution is released matters: some communities live much closer to sources than others. It is a question of environmental justice, and an example of a community's knowledge and advocacy helping to drive action.
How to evaluate an initiative
Ask these questions, and support each answer with evidence:
- What problem does it target (which pollutants, from which sources)?
- Did it work? Look for measured changes in emissions or air quality after it began. Remember that other changes happened at the same time.
- What did it cost, and who paid?
- Who benefits and who might be left out? Are some communities still exposed?
- Side effects: does it move pollution elsewhere, or create a new problem?
- Source quality: is the information from a government agency, a scientific report, a company or an advocacy group? What might each one's perspective be?
Worked exampleExample 1: Evaluating the coal phase-out
Use the evaluation questions to assess Ontario's coal phase-out briefly.
- Problem: coal plants released SO₂, NOx, PM, mercury and large amounts of CO₂.
- Effectiveness: these emissions from Ontario's power sector fell as the plants closed, and smog advisory days became much rarer. But vehicle improvements and U.S. reductions happened at the same time, so not all of the change can be credited to the phase-out.
- Costs: building replacement generation was expensive, and electricity prices were a concern for many people.
- Side effects: natural gas plants filled some of the gap; they emit less SO₂ and PM than coal but still emit CO₂ and NOx.
- Sources: check government reports and independent studies, not just one opinion.
A strong evaluation concludes that the phase-out effectively reduced several pollutants, with real costs and some trade-offs, and supports each point with evidence.
Worked exampleExample 2: Interpreting the AQHI
The AQHI in your town is forecast to be 8 tomorrow afternoon. Your soccer practice is outdoors, and a teammate has asthma. What should the team consider?
- An AQHI of 8 is in the high risk range (7 to 10).
- At-risk people, including people with asthma, are advised to reduce or reschedule strenuous outdoor activity at this level, and everyone should consider reducing it, especially if they notice symptoms like coughing or throat irritation.
- Options: move practice indoors, shorten it, make it less intense, or reschedule; check the forecast because AQHI often changes during the day.
Move or reschedule strenuous activity, especially for the teammate with asthma, and check the updated forecast.
Hands-on activityAir quality watch
You need: internet access (the WeatherCAN app or Environment and Climate Change Canada's website both show the AQHI), a notebook, and your carbon footprint audit from the last lesson.
- For 7 days, record your community's AQHI at about the same time each afternoon, plus the weather (temperature, sunny or cloudy, wind direction, rain). Note anything unusual, such as wildfire smoke or a smog statement.
- Graph AQHI against the day. Mark the risk categories on the graph.
- Analyse: which days were highest? Use your knowledge of ozone, PM2.5 and NO₂ to suggest why (heat and sunshine, wind from a city or a fire, an inversion).
- Evaluate an initiative: choose one Canadian initiative from this lesson. Find one government source and one other source about it. Write a paragraph using the evaluation questions. Name each source and its possible perspective.
- Connect: which of the actions from your carbon footprint audit would also help local air quality, and which would only reduce CO₂?
What to look for: a clear link between your data and chemistry (for example, "Wednesday was hot and sunny with light winds, which favours ground-level ozone formation"), and an evaluation that uses evidence rather than opinion.
Just for funCanada has thousands of lakes, so when acid rain was at its worst, scientists had plenty of places to test. Some lakes in the Experimental Lakes Area in northwestern Ontario were even acidified on purpose, under careful study, to see exactly what acid does to an ecosystem. It's one of the few places where scientists get to do experiments with whole lakes.
Your turn
1Which three pollutants are used to calculate the AQHI?
Ground-level ozone (O₃), fine particulate matter (PM2.5) and nitrogen dioxide (NO₂).
2What risk category is an AQHI of 5? Of 9?
5: moderate risk. 9: high risk.
3Why was the Canada–United States Air Quality Agreement needed?
SO₂ and NOx from one country were carried by wind to the other, causing acid rain and smog across the border. Neither country could solve the problem alone.
4Give two reasons smog advisories became rarer in Ontario after the early 2000s.
Ontario stopped burning coal for electricity (by 2014), and vehicles and fuels became cleaner (also, U.S. emissions fell).
5What is environmental justice? Use Aamjiwnaang First Nation as an example.
The idea that all communities deserve equal protection from pollution and a voice in decisions. Aamjiwnaang is surrounded by industrial facilities, so its members face more exposure than most people, and the community has pushed for better monitoring and stricter rules.
6Why did Ontario end Drive Clean testing for passenger vehicles?
Modern passenger vehicles had become much cleaner, so the tests found few problems compared with the cost; heavy-duty vehicle testing continued.
More practice: warm-up
1What does AQHI stand for?
Air Quality Health Index.
2What range of AQHI values is low risk?
3In what year did Ontario's last coal-fired station stop burning coal?
4Which pollutant is usually highest on hot, sunny summer afternoons?
5What is a temperature inversion?
A layer of warm air above cooler air near the ground, which traps pollutants near the surface.
More practice: on your own
1Using the sample AQHI week, describe the trend and suggest a cause for the peak.
Low to moderate (3 to 4) from Monday to Wednesday, a peak of 9 to 10 on Thursday and Friday, then a drop to 3 by Sunday. The peak matches wildfire smoke, which adds a lot of PM2.5; the drop suggests the wind changed direction or rain cleared the air.
2Explain why low-sulfur gasoline helps air quality in two ways.
Less sulfur in fuel means less SO₂ in exhaust, and sulfur damages catalytic converters, so low-sulfur fuel keeps converters removing CO, NOx and hydrocarbons effectively.
3A company's report says its new plant "meets all air quality standards". What questions should you ask before accepting this?
Which standards, and for which pollutants? Who measured it, and is the data public? Where are the monitors compared with nearby homes? Are there cumulative effects with other plants nearby? Is the source independent?
4Why can it be hard to prove that one initiative caused an improvement in air quality?
Many things change at once (other regulations, the economy, weather, emissions from other countries), so improvements can't all be credited to one initiative without careful comparison.
5Name one action that reduces both CO₂ and smog-forming pollutants, and one that reduces only smog-forming pollutants.
Both: driving less (less fuel burned). Only smog-forming: a catalytic converter (it reduces CO, NOx and hydrocarbons but not CO₂).
Challenge
1Evaluate carbon pricing as a way to improve air quality. Consider at least one benefit, one drawback and one way to measure its effect.
Benefit: it gives everyone a reason to burn less fuel, which reduces CO₂ and also NOx, CO and PM. Drawback: costs can fall harder on households that must drive long distances or heat with fuel, and the public may oppose it (Canada set the consumer fuel charge to zero in 2025). Measure: compare fuel sales and emissions before and after, accounting for other changes such as fuel prices and the economy.
2An AQHI reading is 10+ in a town on a smoky day. Explain, using the KMT and Dalton's law, why the concentration of PM2.5 can matter even though particles are a tiny fraction of the air.
Health effects depend on how many harmful particles or molecules you breathe, not their percentage. Each breath (about 0.5 L) contains a huge number of particles; at high concentrations, many reach deep into the lungs. Just as oxygen's partial pressure (not its percentage) controls how much enters the blood, the amount of a pollutant per litre of air controls the dose you receive.
3Design a simple community air-monitoring plan for a neighbourhood near a highway. Include what to measure, where, when, and how to share results.
Measure NO₂ and PM2.5 (the AQHI pollutants most linked to traffic), using low-cost sensors or passive NO₂ samplers checked against an official station. Place monitors at several distances from the highway (e.g. 50 m, 200 m, 500 m) and near a school. Record hourly, including rush hours, weekends and different seasons. Share results publicly with maps and graphs, and work with local residents (and, where relevant, First Nations, Inuit and Métis communities) to decide what questions matter and how data is used.
Quiz
1. The AQHI combines the health risks from which pollutants?
3. The 1991 Canada–United States Air Quality Agreement first focused mainly on:
4. Ontario's last coal-fired electricity station stopped burning coal in:
5. Which question is MOST important when deciding whether an initiative actually improved air quality?
6. Aamjiwnaang First Nation's air quality concerns are an example of:
Big idea (F1.2, with A2.1): students assess local air quality using the AQHI and other data, and evaluate Canadian initiatives (the Canada–U.S. Air Quality Agreement, Ontario's coal phase-out, vehicle and fuel standards, Drive Clean, national standards, carbon pricing) with evidence, considering effectiveness, costs, side effects and who is affected.
Careers: air quality monitoring and analysis involves atmospheric chemists, environmental technologists, public-health specialists, engineers and policy analysts. If your teen is interested, look at job descriptions with them.
How to help: check the AQHI together for a week, and talk about an initiative in the news. Encourage your teen to separate evidence from opinion and to note who wrote each source.
Sensitive content: the Aamjiwnaang example involves a living community's real health concerns. Discuss it respectfully, focusing on the community's leadership and the science of exposure.
Common difficulties:
- Treating any decline as proof an initiative worked. Many causes act at once.
- Mixing up AQHI pollutants with greenhouse gases. The AQHI doesn't include CO₂.