This document provides the most up-to-date list of the Ambient Air Quality Criteria (AAQC) set by the Ontario Ministry of the Environment, Conservation and Parks, and a brief description of the process used by the Ministry to develop the AAQCs.

An AAQC is not a regulatory value. It is a concentration of a contaminant in air that is protective against adverse effects on health and/or the environment. AAQCs are used to assess general (ambient) air quality resulting from all sources of a contaminant to air. AAQCs are most commonly used in environmental assessments, special studies using ambient air monitoring data, assessment of general air quality in a community and annual reporting on air quality across the province.

Since AAQCs are based on a review of scientific information about the effects of contaminants on health and the environment, they may be modified from time to time based on new or relevant scientific information.

AAQCs are based on effects

AAQCs are based on the most sensitive effect identified through a review carried out at the time of AAQC development. Most AAQCs are based on health effects.

The health effects considered during the process of developing an AAQC may be acute (for example, pulmonary irritation) or chronic (for example, a life-time increased risk of cancer) and this, in turn, affects the averaging time assigned to the AAQC. Averaging times for AAQCs intended to protect against acute effects are generally less than 24 hours (for example, 1 hour), whereas averaging times for AAQCs protective against chronic effects are generally 24 hours or longer (for example, 30 days, annual).

The list of AAQCs provided in the document has also incorporated the Canadian Ambient Air Quality Standards (CAAQS) for the fine fraction of particulate matter, i.e. the atmospheric particulate matter that have a diameter of less than 2.5 micrometers or PM2.5. CAAQS are developed through the Canadian Council of Ministers of the Environment as part of an established Air Quality Management System (AQMS). AQMS is a collaborative framework for improving air quality across Canada, and CAAQS are set nationally for public-reporting and air quality management. For more details, the 2012 “Guidance Document on Achievement Determination: Canadian Ambient Air Quality Standards for Fine Particulate Matter and Ozone” by the Canadian Council of Ministers of the Environment, should be consulted.

Contaminants with more than one AAQC

For some contaminants, more than one AAQC may be set either because more than one effect is identified for the contaminant, or the AAQC based on a specific effect and averaging time may be converted to a different value based on a different averaging time. These scenarios are briefly described below:

  1. If more than one effect is identified for a contaminant, then more than one AAQC is set and all of them are to be used for assessment purposes.

    Example: Chlorine has a 24-hr AAQC based on health effects associated with long-term exposures (respiratory epithelial damage), and a 10-minute AAQC based on the level at which people may detect the odour in short-term exposures.

  2. For some contaminants, a second AAQC may be set based on the conversion of the original value to reflect a different averaging time. For converting the AAQC from one averaging time to another, the Ministry uses the methods and rules described in the Ontario Regulation 419/05, section 17.

Converted AAQCs may be used to address implementation issues (associated with monitoring and/or modelling of contaminants) and are most often applied to allow assessment of data collected over shorter time periods. In these cases, if the converted AAQC is exceeded, then additional assessment may be warranted to understand potential health or environmental effects.

Organization of the AAQC list

The AAQC List consists of seven columns containing the following information:

Column 1 (No.): contaminant counter

Column 2 (CASRN): Chemical Abstracts Service Registry Number for each contaminant

Column 3 (Contaminant): the name of the contaminant listed in alphabetical order

Column 4 [AAQC (µg/m3)]: the AAQC concentration value typically expressed in micrograms per cubic metre (µg/m3), unless other units such as parts per billion (ppb) or parts per million (ppm) are specified. For those concentrations expressed as both ppb/ppm and µg/m3, the following conditions were applied: 10°C and a pressure of 101.3 kilopascals. For sulphur dioxide, only the ppb value is shown in the table for the AAQCs for implementation purposes. For some metals, AAQCs for particulate matter of different size fractions are provided in the list. For example, for manganese and manganese compounds (CAS # 7439-96-5), there is one AAQC for the metal in ambient PM2.5, another in PM10 (the fraction of particles with an aerodynamic diameter smaller than 10 µm), and a third one in suspended particulate matter (SPM). The metal concentration in the lowest particulate size fraction is considered as the most relevant from a toxicological perspective. The AAQCs for the larger particulate fractions may be used to address implementation issues associated with monitoring and/or modelling of contaminants.

Column 5 (Averaging Time): averaging time period

Column 6 (Basis): basis of the AAQC, which may be one of the following:

Corrosion: Deterioration of a surface resulting from a chemical reaction involving the air contaminant.

Effects on animals: Toxicity to foraging animals.

Health: Adverse health effects that could occur from short-term or long-term exposure to the contaminant in air.

Odour: Geometric mean of odour detection thresholds available for the contaminant. Odour-based AAQCs with averaging times other than 10 minutes are to be updated to align with the current ministry approach for setting odour-based criteria.

Particulate or visibility: AAQCs with this designation are based on the assumption that the contaminant is more likely emitted as SPM, and therefore the AAQC for SPM is applied. Particulates influence visibility in air.

Soiling: Effects on aesthetics from the deposition of the contaminant.

Vegetation: Toxicity due to deposition on or uptake of the contaminant by plants.

Column 7 (Notes): Notes with additional information, for example whether the AAQC is a converted value and how to apply the AAQC.

List of Ambient Air Quality Criteria (AAQCs)

Appendix: dioxins, furans and dioxin-like PCBs to which the AAQC applies

Application of the AAQC for dioxins, furans, and dioxin-like PCBs requires the calculation of the total toxicity equivalent (TEQ) concentration contributed by all dioxin-like compounds in the mixture by using the following formula:

A = Σ(B × C), where

the amount (or concentration) of total dioxins, furans and dioxin-like PCBs in TEQ
the amount (or concentration) of each dioxin-like compound listed
the corresponding TEF for each dioxin-like compound listed, according to the reevaluation conducted in 2005 by the World Health Organisation (Van den Berg et al., Toxicol Sci. 2006; 93: 223-41)

This scheme is intended to be used with isomer specific analytical results. For the purpose of calculating the total TEQ concentration for a mixture of dioxin-like compounds, a value of half the minimum detection limit (MDL) should be substituted for concentrations less than the MDL.

Other PCBs (i.e. the non-dioxin-like PCBs) are to be evaluated against the existing AAQC for PCBs (CAS 1336-36-3).

No. CASRN Dioxins, furans and dioxin-like PCBs WHO2005 TEFs
1 1746-01-6 2,3,7,8-Tetrachlorodibenzo-p-dioxin [2,3,7,8-TCDD] 1
2 40321-76-4 1,2,3,7,8-Pentachlorodibenzo-p-dioxin [1,2,3,7,8-PeCDD] 1
3 39227-28-6 1,2,3,4,7,8-Hexachlorodibenzo-p-dioxin [1,2,3,4,7,8-HxCDD] 0.1
4 57653-85-7 1,2,3,6,7,8-Hexachlorodibenzo-p-dioxin [1,2,3,6,7,8-HxCDD] 0.1
5 19408-74-3 1,2,3,7,8,9-Hexachlorodibenzo-p-dioxin [1,2,3,7,8,9-HxCDD] 0.1
6 35822-46-9 1,2,3,4,6,7,8-Heptachlorodibenzo-p-dioxin [1,2,3,4,6,7,8-HpCDD] 0.01
7 3268-87-9 1,2,3,4,6,7,8,9-Octachlorodibenzo-p-dioxin [1,2,3,4,6,7,8,9-OCDD] 0.0003
8 51207-31-9 2,3,7,8-Tetrachlorodibenzofuran [2,3,7,8-TCDF] 0.1
9 57117-41-6 1,2,3,7,8-Pentachlorodibenzofuran [1,2,3,7,8-PeCDF] 0.03
10 57117-31-4 2,3,4,7,8-Pentachlorodibenzofuran [2,3,4,7,8-PeCDF] 0.3
11 70648-26-9 1,2,3,4,7,8-Hexachlorodibenzofuran [1,2,3,4,7,8- HxCDF] 0.1
12 57117-44-9 1,2,3,6,7,8-Hexachlorodibenzofuran [1,2,3,6,7,8-HxCDF] 0.1
13 72918-21-9 1,2,3,7,8,9-Hexachlorodibenzofuran [1,2,3,7,8,9- HxCDF] 0.1
14 60851-34-5 2,3,4,6,7,8-Hexachlorodibenzofuran [2,3,4,6,7,8- HxCDF] 0.1
15 67562-39-4 1,2,3,4,6,7,8-Heptachlorodibenzofuran [1,2,3,4,6,7,8- HpCDF] 0.01
16 55673-89-7 1,2,3,4,7,8,9-Heptachlorodibenzofuran [1,2,3,4,7,8,9- HpCDF] 0.01
17 39001-02-0 1,2,3,4,6,7,8,9-Octachlorodibenzofuran [1,2,3,4,6,7,8,9-OCDF] 0.0003
18 32598-13-3 3,3',4,4'-Tetrachlorobiphenyl [3,3',4,4'-tetraCB (PCB 77)] 0.0001
19 70362-50-4 3,4,4',5- Tetrachlorobiphenyl [3,4,4',5-tetraCB (PCB 81)] 0.0003
20 57465-28-8 3,3',4,4',5- Pentachlorobiphenyl (PCB 126) [3,3',4,4',5-pentaCB (PCB 126)] 0.1
21 32774-16-6 3,3',4,4',5,5'- Hexachlorobiphenyl [3,3',4,4',5,5'-hexaCB (PCB 169)] 0.03
22 32598-14-4 2,3,3',4,4'- Pentachlorobiphenyl [2,3,3',4,4'-pentaCB (PCB 105)] 0.00003
23 74472-37-0 2,3,4,4',5- Pentachlorobiphenyl [2,3,4,4',5-pentaCB (PCB 114)] 0.00003
24 31508-00-6 2,3',4,4',5- Pentachlorobiphenyl [2,3',4,4',5-pentaCB (PCB 118)] 0.00003
25 65510-44-3 2',3,4,4',5- Pentachlorobiphenyl [2',3,4,4',5-pentaCB(PCB 123)] 0.00003
26 38380-08-4 2,3,3',4,4',5- Hexachlorobiphenyl [2,3,3',4,4',5-hexaCB (PCB 156)] 0.00003
25 69782-90-7 2,3,3',4,4',5'- Hexachlorobiphenyl [2,3,3',4,4',5'-hexaCB (PCB 157)] 0.00003
28 52663-72-6 2,3',4,4',5,5'- Hexachlorobiphenyl [2,3',4,4',5,5'-hexaCB (PCB 167)] 0.00003
29 39635-31-9 2,3,3',4,4',5,5'- Heptachlorobiphenyl [2,3,3',4,4',5,5'-heptaCB (PCB 189)] 0.00003


For additional technical information regarding the AAQCs and contaminants included, please contact:

Human Toxicology and Air Standards Section
Technical Assessment and Standards Development Branch
Ontario Ministry of the Environment, Conservation and Parks
Email: GLCCoordinator@ontario.ca

Suggested citation

Human Toxicology and Air Standards Section, Technical Assessment and Standards Development Branch, Ontario Ministry of the Environment, Conservation and Parks (MECP). 2020. Ontario’s Ambient Air Quality Criteria. MECP, Toronto, ON, Canada.

ISBN: 978-1-4868-4499-9