Canadian Environmental Quality Guidelines

Canadian Council of Ministers of the Environment, 1999

Abstract

National ambient air quality objectives (NAAQOs)

(Appendix 1) are the benchmark against which Canada

assesses the impact of anthropogenic activities on air

quality and ensures that current emission control policies

are successfully protecting human health and the

environment. Air quality objectives are designed to

facilitate air quality management on regional scales. A

new framework for ambient air quality objectives has been

developed that is more scientifically defensible and

accommodates the current understanding of ambient

pollutant effects. Specifically, it acknowledges the

continuum of receptor effects and the existence of no, or

very low, threshold pollutants. This chapter describes the

new framework and the process by which NAAQOs are

developed.

The process of developing NAAQOs begins with a

scientific assessment of dose–response relationships for

receptors (human health, vegetation, animals, and

aesthetic atmospheric properties), ambient exposures, and

receptor risk characterization. Recently, scientific

assessments have been completed for carbon monoxide,

hydrogen fluoride, particulate matter, and ozone.

To support the development of the air quality objective,

risk benefit analyses are performed to provide an

indication of the magnitude of current and/or anticipated

impacts on human health and/or the environment.

Introduction

The purpose of this chapter is to provide an overview of

the new framework and process that has been developed

for Canadian national ambient air quality objectives. The

federal government sets national ambient air quality

objectives (NAAQOs) on the basis of recommendations

from the Federal–Provincial Working Group on Air

Quality Objectives and Guidelines consisting of

representatives from both the health and environment

departments. Objectives may be promulgated by

Environment Canada and/or Health Canada under the

Canadian Environmental Protection Act (CEPA), Part 1,

Section 8, and adopted by provincial and territorial

jurisdictions for enforcement as standards. The NAAQOs

are the benchmark against which Canada can assess the

impact of anthropogenic activities on air quality and

ensure that current emission control policies are successfully protecting human health, vegetation, materials,

and/or aesthetic air quality parameters. The objectives are

designed to facilitate air quality management on a regional

scale.

The New Framework

The first Canadian NAAQOs were developed in the mid1970s (Fisheries and Environment 1976) for sulphur

dioxide, suspended particulates, carbon monoxide,

oxidants (ozone), and nitrogen dioxide. These objectives

consisted of three tiers which identified ranges of air

quality designed to meet the varied needs for air quality

objectives across Canada (SOE 1990).

In 1992, the Canadian Environmental Protection Act/

Federal–Provincial Advisory Committee (CEPA/FPAC)

Working Group on Air Quality Objectives and Guidelines

(Appendix 2) was established to review existing and

develop new air quality objectives. During the review of

the most recent human health and environmental effects

literature, it became apparent that many air pollutants had

no effect thresholds or very low effect thresholds, making

it impossible to define more than one effect level.

Consequently the three-tiered framework became

untenable in light of the observed continuum of receptor

effects. The need for a more scientifically sound

framework for Canada’s NAAQOs was identified.

The new NAAQOs framework for Canada is more

scientifically defensible and recognizes the existence of

no, or very low, threshold pollutants. The new framework

specifies a scientifically determined level above which

there are known effects on human health or the environment, and an air quality objective, also science based,

which considers the protection of the general population

and environment. The two levels areas follows.

• The reference level is a level above which there are

demonstrated effects on human health and/or the

environment. It provides a scientific basis for

Canadian National Ambient Air Quality Objectives:

Process and Status
Canadian National Ambient Air Quality Objectives:

Process and Status

2

establishing goals for air quality management.

Reference levels are defined for all receptors for which

effects information is available (human health, animals,

vegetation, materials, and aesthetic atmospheric

parameters). Demonstrated effects are in the area

bounded by the no-observed-effect level and the

lowest-observed-effect level. Recognizing that the

dose–response relationship and/or concentration–

response relationship may be continuous, the

identification of a “demonstrated effect” may be either

statistically or observationally derived.

• National ambient air quality objectives are national

goals for outdoor air quality that protect public health,

the environment, or aesthetic properties of the

environment. They are targets for air quality, measured

at relevant receptors (e.g., persons, plants, animals,

materials). When an air quality objective is

recommended, a rationale document summarizes the

relevant scientific information, the risk assessment, and

the current and anticipated exposures, and presents the

explanation for the selection of the selection of the

form and level of the air quality objectives.

The reference level is based on consideration of the

scientific factors without regard for other factors. It is

recognized that risk assessment judgments are to some

extent policy judgments in which disagreements largely

reflect policy values (including moral, social, economic,

or other nonscientific values). Additional factors can be

taken into account in selecting the air quality objective

including (1) data on the public health and ecological

effects (estimated risks) expressed in terms of measures of

incremental impact on various endpoints (e.g., morbidity

and/or mortality, transient and persistent effects on the

ecosystem), at different exposure levels; (2) an expression

of the confidence in the data; (3) data on current and

future trends in ambient air pollutant levels; and (4) an

exceedance analysis of proposed air quality objectives.

The science assessment activity is the foundation of the

new framework and summarizes the most current

published science available in a Canadian context. It

forms the foundation from which all discussions oriented

toward managing air quality proceed. The new framework

recognizes that it is not feasible to protect all members of

a receptor population from adverse effects of air pollution

at all times. Consequently, for the selection of the air

quality objective, a subjective decision based on the best

information available is required.

Given the need to make subjective scientific decisions

based on a broad range of scientific information to define

the air quality objective, the following general concepts

have been developed to guide the process (WGAQOG

1996):

1. Be consistent with the philosophy of CEPA.

2. Recognize the variable sensitivities of subgroups of

the Canadian population and of particular ecosystems

and organisms in the environment. Given the large

range of these sensitivities, it may not be possible to

protect every sensitive individual and ecosystem from

all effects.

3. Provide a range of levels reflecting the range of

biological responses and sensitivities, allowing for

various regulatory options to accommodate regional

priorities while endeavouring to maintain consistent

national levels of environmental quality.

4. Be reasonable, workable, and usable, reflecting a

consultative process that includes government,

industry, public advocacy groups, and the Canadian

public, and recognizes the importance of scientific,

social, and economic considerations.

5. Be based on recognized scientific principles and

include risk assessment and risk management. The

scientific basis for objectives should be presented in a

manner that is readily accessible to, and which can be

understood by, the Canadian public.

In addition three other concepts are also considered:

1. To contribute to sustainable development through

pollution prevention, an ecosystem approach, maintenance of biodiversity, and the precautionary principle.

2. To consider other sources of exposure on a chemicalspecific basis to account for the quality and quantity of

total exposure.

3. To follow a development and consultation process that

is fully transparent.

Process

The process by which information is reviewed, evaluated,

and utilized in developing air quality objective
Canadian National Ambient Air Quality Objectives:

Process and Status

3

recommendations is outlined in detail in the Protocol for

the Development of National Ambient Air Quality

Objectives (WGAQOG 1996). Briefly, the process starts

with the identification of the need for an objective,

followed by the scientific assessment and evaluation of

receptor effects information for human health, vegetation,

animals, materials, and aesthetic impacts. A reference

level is derived for those receptors for which sufficient

information exists to identify the concentration/dose–

response relationship. The science assessment document,

containing the reference level, is reviewed by external

scientific peers and distributed for national stakeholder

consultation.

A rationale document supporting the recommended air

quality objective is prepared summarizing the science

assessment document and outlining the various options

considered and the incremental risk benefit assessment.

The draft rationale document is distributed for high-level

national stakeholder consultation to solicit comments and

input to the recommendations. Where necessary, revisions are

made and the final recommendations are made to

CEPA/FPAC for federal approval. The NAAQO is published

in the Canada Gazette, Part 1. It is estimated that the process

to review the science and recommend air quality objectives

requires three to five years depending on the amount and

certainty of the current scientific understanding.

Selection Criteria and Interim Recommendations

Nomination of air contaminants for review are made by

the public, industry, and government agencies through

various federal–provincial-stakeholder fora. Based on

guidelines developed by the United Nations World Health

Organization (WHO 1989), the following criteria are used

to determine the need for extensive evaluation

(WGAQOG 1996):

• capability of the substance to cause adverse effects on

human health or the environment, where irreversible

effects are of special concern;

• ubiquity and abundance of the substance in the

Canadian environment, particularly in the atmosphere;

• environmental transformations to form secondary

pollutants or metabolic alterations, when these

alterations may lead to the production of chemicals

with greater toxic potential;

• persistence in the environment, particularly if the

pollutant would resist environmental degradation and

accumulate in humans and food chains;

• likelihood of effects, magnitude of the population

exposed, and the existence of sensitive subpopulations;

• current or potential relevance to Canada as a national

concern for more than one province and/or territory, and

priorities of local air quality management jurisdictions;

• appropriateness of managing the substance from a

regional/airshed versus site specific approach; and

• appropriateness of managing the substance using air

quality objectives, in contrast with other available or

established management options.

In the event of significant scientific uncertainty or of

limited information relevant to the Canadian context, the

science assessment document will be completed and

reference levels may be identified. Depending on the state

of knowledge, an interim air quality objective or no air

quality objective may be recommended. Interim recommendations are intended to encourage the scientific

community to address knowledge gaps. They also signify

the need to consider a preventive, precautionary approach

to the management of the air contaminant.

Science Assessment

The science assessment document provides a review of the

following issues: physical and chemical properties of the

substance, environmental fate and behaviour, identification

and characterization of emission sources, ambient monitoring

technologies, and environmental levels. Receptor effects are

reviewed for each of the following receptors for which

information is available: human health, vegetation, animals,

materials, and aesthetic parameters (odour and visual range).

The human health assessment reviews available clinical,

toxicological, and epidemiological information. Vegetation

receptors are subdivided in the review process to evaluate

impacts on agricultural species, forest species, horticultural

species, and natural ecosystems. Animal receptors are

reviewed as livestock, mammalian wildlife, and birds.

Material receptors are typically elastomers, textiles, and

building materials.

The receptor effects review attempts to characterize

(qualitatively and quantitatively) the toxicity of the air
Canadian National Ambient Air Quality Objectives:

Process and Status

4

contaminant. The qualitative assessment establishes the

adequacy of the scientific data base to derive and support

the reference level. At this stage, the consistency of the

data base and limitations imposed by irreconcilable

contradictions is expressed. During the qualitative

assessment, the type of effects (e.g., chronic vs. acute,

reversible vs. nonreversible, threshold vs. nonthreshold),

the relevance of the effect to other species or receptors,

the identification of susceptible or sensitive species and

subpopulations, and the relevance to the Canadian context

are established.

The quantitative assessment in its simplest form is a

numerical expression of the concentration/dose–response

relationship. There are two general cases: threshold and

nonthreshold. A threshold endpoint is one in which there

is measurable level below which there is no discernible

effect on the receptor. Above the threshold, there is a

dose–response relationship that can be quantified. The

threshold is often called the no-observable-adverse-effect

level (NOAEL). Where it is not possible to define the

NOAEL, there may be an expression of the lowestobservable-adverse-effect level (LOAEL), which

indicated the likelihood of threshold’s existence.

Nonthreshold endpoints are those in which the effect is

proportional to the concentration with no definitive loss of

the relationship, that is, no concentration at which the

effect ceases to be observed.

For receptors for which reference levels are identified, an

exposure assessment is performed. This exposure

assessment uses available ambient data to establish the

exposure of Canadian receptors to the air contaminant.

This information is relevant to the risk characterization.

The depth and accuracy of the exposure assessment are

tailored to the degree of knowledge required to support

the risk estimation, and to support the development of

focused air quality management strategies.

The risk characterization attempts to define the nature and

degree of hazard posed by the air contaminant at known or

current exposure levels. An accurate and unbiased

discussion of the significance of the data is required, as is

information on a variety of endpoints that provide insight

into the full spectrum of responses in a number of

receptors. Estimates of the proportion of the receptor

populations above a specified level of risk, NOAEL, or

LOAEL are made which provide an indication of the

likelihood of occurrence of the adverse effects associated

with exposure to the air contaminant.

Derivation of the Reference Level

In the derivation of the reference level, the science

assessment becomes more than a literature review. The

information is evaluated to determine the receptors for

which there is sufficient information to develop a

reference level, and of those receptors, which are relevant

to Canada. That is, the receptor should be present in

Canada, or extrapolation of the measured endpoint to an

effect on a Canadian receptor should be possible. The

conditions under which the experiments reported in the

literature are performed should occur or be expected to

occur in Canada. There should be general consensus

among the scientific community regarding the quality of

the results and the conclusions regarding the receptor

effect upon which the reference level is based.

The weight-of-evidence approach is the preferred

approach for deriving the reference level and is used when

there are many quality studies upon which to base the

concentration/dose–response relationship. For some air

contaminants there may be one study that is particularly

relevant to Canada, only one study in which

environmentally relevant air contaminant concentrations

were used, or one study that stands out as being the most

comprehensive or applicable in the Canadian context. In

such cases, it may be appropriate to use a definitive study

approach to the derivation of the reference level. In this

case, a single study is selected as best representing the

concentration/dose–response relationship and the

conditions expected in the Canadian environment. The

weight of evidence is provided in summary format to

support the definitive study and the identification of the

reference level.

In deriving a reference level, the variability in receptor

response must be distinguished from the uncertainty in

defining the response. Both of these factors are considered

explicitly. In determining the reference level the level of

uncertainty associated with that level is identified. In a

weight-of-evidence approach, the reference level is the

best estimation from a number of different tests; thus there

will be uncertainty associated with the derived dose and

ambient concentration.

The reference level is the level above which there are

demonstrated effects on human health and/or the

environment. It is scientifically based and defines the

boundary between the LOAEL and the NOAEL. It is

considered to be the level of exposure just below that
Canadian National Ambient Air Quality Objectives:

Process and Status

5

most likely to result in a defined and identifiable but

minimal effect. The reference levels have no safety factors

applied to them, as they are related directly to the

LOAEL, and are the most conservative estimates of the

effect level.

Development of Air Quality Objective Options

The air quality objectives are designed to be targets for

federal, provincial, or regional air quality management

activities. They represent decision making in light of

available scientific information on effects, the continuum

of receptor effects down to very low concentrations (i.e.,

the lack of a dose–response threshold), and the level of

risk posed by the air pollutant. Selection of a risk-based

objective acknowledges that zero risk will not be

achieved. Given the diverse nature of factors that may be

considered in selecting the objective and the uncertainties

associated with the estimates of the toxicological risk, the

selection of the objective is inherently subjective and open

to debate.

Options are developed based primarily on the scientific

considerations of incremental risk, current ambient

exposures, and the lowest level at which effects have been

identified in a receptor population or significant sensitive

subgroup. Selection of the final air quality objective

recommendation reflects the guidance to be reasonable

and workable in light of developing regional and national

air quality management strategies.

Current Status

In the past few years the Federal–Provincial Working

Group on Air Quality Objectives and Guidelines has

developed a protocol for reviewing the science and

deriving the reference levels and has completed science

assessment documents for hydrogen fluoride, carbon

monoxide, and particulate matter (PM <10 and PM <2.5).

Reference levels have been derived for hydrogen fluoride

and particulate matter. Work is currently under way to

prepare science assessment documents for ozone and total

reduced sulphur compounds. Following completion of

these reviews, the existing NAAQOs for nitrogen dioxide

and sulphur dioxide will be reviewed.

Current harmonization initiatives under the Canadian

Council of Ministers of the Environment framework are

working toward the development of Canada-wide

standards (CCME 1997). These standards encompass

qualitative or quantitative standards, guidelines,

objectives, and criteria for protecting the environment and

human health. The primary focus is on ambient

environmental standards for the quality of air, water, soil,

biota, other media, and for other components of

ecosystems as well as ecosystems themselves. Particulate

matter and ozone have been identified as priority

substances for the development of Canada-wide standards

under the harmonization agreement. Canada-wide

standards for particulate matter and ozone will be

developed based on the NAAQO science assessments, and

air quality objectives will not be identified.

Conclusions

The new framework for air quality objectives in Canada

has facilitated the review of existing objectives and the

development of new objectives. It has allowed for a

credible and peer-reviewed science assessment to form the

basis for the NAAQOs, yet provides the flexibility to

recognize the broad range of receptor sensitivities and the

regional nature Canadian air quality problems. It is a

system that is working.

References

CCME (Canadian Council of Ministers of the Environment). 1997.

http://www.ccme.ca/ccme/harmonization.html. March 23, 1997.

Fisheries and Environment Canada. 1976. Criteria for national air

quality objectives: Sulphur dioxide, suspended particulates, carbon

monoxide, oxidants (ozone) and nitrogen dioxide. Reports to the

Federal–Provincial Committee on Air Pollution (1971 and 1973) by

the Subcommittee on Air Quality Objectives, November 1976,

Ottawa.

Hilborn, J., amd M. Still. 1990. A State of the Environment Report:

Canadian perspectives on air pollution. SOE Report No. 90-1.

WGAQOG (Federal–Provincial Working Group on Air Quality

Objectives and Guidelines). 1996. A protocol for the development of

national ambient objectives, Part 1, Science assessment document and

derivation of the reference level(s). Catalogue #En42-17/5-1-1997E.

Environment Canada and Health Canada, Toronto and Ottawa.

WHO (World Health Organization). 1989. Setting environmental

standards: Guidelines for decision making. H.W. de Koning, ed.

WHO, Geneva.
Canadian National Ambient Air Quality Objectives:

Process and Status

6

Appendix 1

National Ambient Air Quality Objectives

Averaging time

Pollutant 1 hour 24 hour Annual Published Reviewed

Carbon monoxide (mg·m-3 ) D 15 6 (8 h) 1974 1996

A 35 15 (8 h) 1974 1996

T 20 (8 h) 1978 1996

Hydrogen fluoride (μg·m-3 ) RL 1.1 0.5 (7 d) 1997

Nitrogen dioxide (μg·m-3 ) D 60 1975 1989

A 400 200 100 1975 1989

T 1000 300 1978 1989

Ozone (μg·m-3 ) D 100 30 1974 1989

A 160 50 30 1974 1989

T 300 1978 1989

RL *

PM <10 (μg·m-3 ) RL 25 1998

PM <2.5 (μg·m-3 ) RL 15 1998

Sulphur dioxide (μg·m-3 ) D 450 150 30 1974 1989

A 900 300 60 1974 1989

T 800 1978 1989

Total reduced sulphur compounds RL *

AQO *

Total suspended particulates (μg·m-3 ) D 60 1974 1989

A 120 70 1974 1989

T 400 1978 1989

Notes:

D: Desirable

A: Acceptable

T: Tolerable

RL: Reference level

AQO: Air quality objective

*

Reviews in progress.
Canadian National Ambient Air Quality Objectives:

Process and Status

7

Appendix 2

CEPA/FPAC Working Group on Air Quality Objectives and Guidelines and

Secretariat

(Membership as of December 1998)

Alberta Randy Angle Alberta Environmental Protection

Alberta Alex Mackenzie Alberta Health

British Columbia Richard Bennett Ministry of Environment, Lands and Parks

British Columbia Ray Copes Ministry of Health and Ministry Responsible for Seniors

Manitoba Jim Popplow Manitoba Health

Manitoba Jean Van Dusen Manitoba Environment

New Brunswick Mark Allen Department of Health and Community Services

Newfoundland Reginald Coates Department of Health and Community Services

Northwest Territories Jim Sparling Department of Resources, Wildlife and Economic

 Development

Nova Scotia Randy Piercey Department of the Environment

Ontario Lesbia Smith Ontario Ministry of Health

Ontario Akos Szakolcai Ontario Ministry of the Environment

Quebec Pierre Walsh (Co-chair) Ministère de l’Environnement et de la Faune

Quebec Michèle Bélanger Ministère de la Santé

Saskatchewan Gord Will Saskatchewan Environment and Resource Management

Yukon Joe Ballantyne Department of Renewable Resources

Canada Ann McMillan Environment Canada

Canada Barry Thomas (Co-chair) Health Canada

Secretariat Elizabeth Bush Environment Canada

Marjorie Shepherd Environment Canada

Barry Jessiman Health Canada

Kerri Timoffee Health Canada
Canadian National Ambient Air Quality Objectives:

Process and Status

8

Reference listing:

Canadian Council of Ministers of the Environment. 1999. Canadian national ambient air quality objectives: Process and status. In:

Canadian environmental quality guidelines, 1999, Canadian Council of Ministers of the Environment, Winnipeg.

For further scientific information, contact:

Environment Canada

Atmospheric Environment Service

Science Assessment and Policy Integration Division

4905 Dufferin St.

Toronto, ON M3H 5T4

Facsimile: (416) 739-4882

or

Health Canada

Environmental Health Centre

Bureau of Chemical Hazards

Tunney’s Pasture

Ottawa, ON K1A 0L2

© Canadian Council of Ministers of the Environment 1999

Excerpt from Publication No. 1299; ISBN 1-896997-34-1

For additional copies, contact:

CCME Documents

c/o Manitoba Statutory Publications

200 Vaughan St.

Winnipeg, MB R3C 1T5

Phone: (204) 945-4664

Facsimile: (204) 945-7172

E-mail: spccme@chc.gov.mb.ca

Aussi disponible en français.