National Ambient Air Quality Objectives For Particulate Matter - Executive Summary

Introduction

The Canadian Environmental Protection Act (CEPA) Federal/Provincial Working Group on Air Quality Objectives and Guidelines (WGAQOG) is directed by the CEPA Federal-Provincial Advisory Committee (FPAC) to develop National Ambient Air Quality Objectives (NAAQOs) for airborne pollutants and to undertake their periodic reassessment. NAAQOs are established to provide a measure of protection to people and the environment from adverse effects due to airborne pollutants.

NAAQOs are developed in two stages, the first of which is the scientific assessment stage, embodied within the Science Assessment Document. The science assessment process concludes with determination of one or more Reference Levels for the pollutant of concern, through appropriate analyses of the scientific data, as described in A Protocol for the Development of National Ambient Air Quality Objectives: Part 1: Science Assessment Document and Derivation of the Reference Level(s). The Reference Level is a level above which an effect on a receptor (human or environmental) has been demonstrated. Reference Levels may be proposed for one or more time periods (e.g. 24 hour, annual) and for one or more receptors. Monitoring technology, economic benefits, and public/stakeholder consultations are introduced in the second phase, which is derivation of the Air Quality Objective (AQO). The AQO may be selected at the Reference Level, or it may be either lower or higher, depending on background levels of the pollutant, uncertainties in the underlying scientific data, and other considerations as listed above. The process by which AQOs are developed is described in A Protocol for the Development of National Ambient Air Quality Objectives: Part 2: Rationale Document and Derivation of Air Quality Objectives (in progress).

Canadian air quality objectives for particulate matter ( PM) were first developed in the 1970s and were revised in the 1980s. At that time, the understanding was that episodes of severe pollution could result in adverse health and environmental impacts but that lower concentrations of PM, such as those generally experienced across Canada, were not particularly detrimental. Beginning about 1990, serious doubt was cast on this assumption, because of an avalanche of scientific studies emerging from the U.S., Canada, Britain and Europe. These studies demonstrated adverse effects of PM on cardio-respiratory health, including both increased hospitalizations and increased premature mortality at pollutant levels that were often far below the current air quality objectives. These findings have prompted re-examination of PM air quality objectives not only in Canada, but also in the U.S., Britain, the European Community and the World Health Organization.

The reevaluation of particulate air pollution has also led to a shift in focus from total suspended particulates (TSP), which encompasses a wide size range of particles, to particles equal or less than 10 micrometers in diameter ( PM₁₀), and its subfractions ( PM_2.5). This reflects the current belief that it is these smaller particle fractions that are primarily responsible for the observed adverse health and environmental effects.

The Science Assessment Document represents the Canadian reexamination of particulate matter air pollution and its possible consequences on human health and the environment. This document derives Reference Levels 2.5 µm). for PM₁₀ (particles ≤ 10 µm) and (≤ PM_2.5 µm)