Air Quality in the GTA

Wunch Group - University of Toronto, Physics Department in collaboration with Environment and Climate Change Canada
GTA Air Quality Project
About the project
What is PM?
How do PurpleAir sensors work
Live PurpleAir map
Air Quality Guidelines
Links to Relevant Papers & Articles
Contact Information
Back to the GTA-Emissions main page

Click here to learn about the air quality in your community!

About the project

This is a joint University of Toronto and Environment and Climate Change Canada project on measuring particulate matter concentrations in the GTA using PurpleAir sensors.

The quality of our air is fundamental to the health and livelihoods of our communities and environment and yet it is something we often take for granted as Torontonians. Unfortunately, this is not the case for many people and communities. Various illnesses and socioeconomic factors create disparities in who is affected by poor air quality. For instance, studies like this one from California show the discrepancies in air quality that may exist between low-income neighborhoods. The goal of our project is to examine the air quality in the GTA and provide information to residents of the GTA.

Our group studies atmospheric physics at the University of Toronto. We have 27 PurpleAir sensors deployed throughout Toronto, Mississauga, and Scarborough that measure PM10, PM2.5, and PM1.0. This website contains information about our findings. If you have questions or are interested in collaborating with us, please don’t hesitate to reach out! Our contact information is at the bottom.

What is PM?

PM (particulate matter) is a mixture of solid particles and liquid droplets. The environmental and health effects of these particles are largely determined by the size.

Standard Classification of PM based on size:

PM10: Particles or Droplets that have diameters <10 microns
PM2.5: Particles or Droplets that have diameters < 2.5 microns
PM1.0: Particles or Droplets that have diameters < 1.0 microns

Where does PM come from?

Primary sources: Some particles are emitted directly from sources such as construction sites, fires, etc. Based on a study of 51 countries, globally 25% of air pollution from PM2.5 is contributed by traffic, 15% industrial activities, 20% domestic fuel burning, 22% unspecified human sources, and 18% natural dust and salt.
In an urbanized region like the GTA, traffic is a major contributor to pollution. This includes emissions from exhausts, fuel and lubricant combustion, and the wear of brake linings, clutch, and tires.
Domestic fuel burning is also a major contributor of pollution. Wood, coal, and gas fuel used for cooking and heating contributes to household pollution.

Secondary sources: Secondary sources include unspecified sources of human origin that emit gaseous pollutants such as nitrogen dioxide, ammonia, sulfur dioxide, and non-methane volatile organic. These gaseous undergo reactions in the atmosphere that result in secondary particles.
According to this study, 62% of Canada's total PM2.5 is contributed by unspecified sources of human origin.

Health Effects of PM

The smaller the particle, the greater the health risk it poses. Particles with diameters smaller than 10 micrometers have adverse health effects as they can penetrate deep into your lungs and can possibly enter your bloodstream. Finer particles with diameters smaller than 2.5 micrometers pose an even greater health risk.

Groups that are especially vulnerable to PM:
-Older adults
-People with pre-existing health conditions such as heart and lung diseases

Scientific studies have linked PM exposure to:
-premature death in people with heart or lung disease
-nonfatal heart attacks
-irregular heartbeat
-aggravated asthma
-decreased lung function
-increased respiratory symptoms, such as irritation of the airways, coughing or difficulty breathing.

Long-term exposure

Long-term exposure to PM has been associated with reduced lung function, chronic bronchitis, and in the most serious case, premature death.

Short-term exposure

Short term exposure to PM is unlikely to cause any serious health effects in healthy children and adults. However, it may aggravate lung disease and increase susceptibility to respiratory infections.

Environmental Effects of PM

PM is a contributing cause of reduced visibility (haze).
Wind can carry particles across great distances and eventually those particles settle on ground or water. Particles are of various chemical compositions, some of which can have harmful effects:
1. Some particles can make bodies of water (e.g. lakes) acidic
2. Some particles can change the nutrient balance in coastal waters and river basins
3. Some particles can deplete nutrients in soil
4. Some particles damage sensitive forests and farm crops
5. Some particles contribute to acid rain effects
6. Some particles can stain stone

For more information about health and environmental effects, please click HERE

How do the sensors work?

Each sensor consists of two Plantower PMS 5003 laser counters. Each laser counter has a fan that it uses to bring in samples of air and through the laser beam. The laser beam reflects any particles in the sample of air onto a detection plate. The detection plate measures the reflection in pulses. The length of the pulse tells us the size of the particle and the number of pulses determines the number of particles. The sensor then uses a complex algorithm to calculate the PM2.5, PM1.0, PM10.0 mass concentrations in ug/m3.

Real-time Map

PurpleAir Sensor Live Map


Time Series

Air Quality Guidelines

It is essential to enforce PM exposure limits to minimize the adverse health effects on people. For reference, here are some guidelines from the province of Ontario and the WHO.

Ontario Ambient Air Quality Criteria

These are NOT regulatory values. Rather, they are mass concentrations that are protective of adverse health and environmental effects.

-PM2.5 (24-hour average) target is 27 ug/m3
-PM10.0 (24-hour average) target is 50 ug/m3

WHO Air Quality Guidelines

These are WHO's recommended targets for PM:

-PM2.5 (24-hour average) target is 15 ug/m3
-PM10.0 (24-hour average) target is 45 ug/m3

Relevant Papers & Articles

Disparate air pollution reductions during California’s COVID-19 economic shutdown
Los Angeles case study
Evaluation of PM2.5 measured in an urban setting using a low-cost optical particle counter and a Federal Equivalent Method Beta Attenuation Monitor
Fine particle mass monitoring with low-cost sensors: Corrections and long-term performance evaluation
Contributions to cities' ambient particulate matter (PM)

Contact Information

For inquries about our group's research, please reach out to the PI, Debra Wunch:

University of Toronto

Department of Physics, Rm 707A

60 St. George Street

Toronto, ON M5S 1A7

Phone: (416) 946-0408

Fax: (416) 978-8905

Email: dwunch at

For other community questions and feedback, please reach out to Amy or Stephanie (summer research students)!

Amy Mann:

University of Toronto

Department of Physics, Rm 619A

60 St. George Street

Toronto, ON M5S 1A7

Email: amy.mann at

Stephanie Gu:

University of Toronto

Department of Physics, Rm 602

60 St. George Street

Toronto, ON M5S 1A7

Email: at

Leave us a message!


We would like to express our sincere gratitude to all the Churches, businesses, and organizations that have been so kind as to host one of our sensors.

Many thanks to...

Manor Road United Church
All Saints Kingsway
Roncesvalles United Church
Lawrence Park Community Church

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