Particulate matter: A critical Environmental Health issue

Microscopic airborne particles, known as particulate matter, are created by the burning of fossil fuels and by other human and natural activities. There is growing evidence that particulate matter poses a health threat at lower concentrations, and to a broader spectrum of the population, than was previously thought.

For some time it has been known that high concentrations of particulate matter (PM) contribute to cardio-respiratory problems among children, the sick and the elderly, and are linked to the development of symptoms in healthy individuals. However, it is only recently that relatively low concentrations—like those commonly experienced across Canada—have been linked to these effects. The findings are contained in a science assessment published by Environment Canada and Health Canada.

There is no threshold level below which exposure to particulate matter is deemed safe to human health. Adverse effects are specific to the heart and lungs, and include increasing hospitalization (see below) and death rates because of cardio-respiratory diseases, decreased lung function in asthmatics and children, and increases in respiratory stress. Particulate matter also discolours and degrades certain materials, is harmful to vegetation because it blocks photosynthesis by smothering the leaf surface and causing chemical effects to the plant or soil, and reduces visibility outdoors by scattering and absorbing light.

Relationship between sulphate levels (airborne particles) and admissions to hospitals for respiratory problems (Source: Health Canada, 1994 data from southern and eastern Ontario)

Scientists studying the issue are most concerned with tiny particles, the so-called "suspended" portion of PM in air. This "suspended" portion cover particles that are up to 40 micrometres in diameter—about half the width of a human hair. Small particles remain suspended longer, and penetrate deeper into the lungs than larger ones. Of primary interest are those with an upper size limit of 10 micrometres, PM10 as it is known. Researchers are giving particular attention to the particles within that group that are fine (<2.5) and ultrafine (<0.1).

While coarse particulate matter comes from both natural sources, such as windblown soil, pollen, volcanic dust and bacteria, and human-caused sources, like construction or road dust, most fine particles are formed through chemical reactions involving gases and other particles in the atmosphere. The most common precursors to these reactions are nitrogen oxides, sulphur dioxide and volatile organic carbons emitted by the burning of fossil fuels and other industrial processes.

Data on ambient particulate matter levels in cities and rural areas show marked differences in concentrations and characteristics across Canada. Montréal, Windsor, Hamilton, Walpole Island (near Detroit) and Calgary have the highest PM10 levels, with Vancouver and the Windsor-Québec City corridor topping the PM2.5 charts. Pronounced weekly cycles showing the lowest concentrations on Sundays and the highest mid-week also support the connection with human-caused sources.

Many aspects of the particulate matter issue require further study, including the role that particle size, mass and composition play in health impacts. Environment Canada's contribution to this growing body of knowledge includes research on the characterization of ambient particulate matter levels, the composition of particles, the processes involved in its formation, emission and precursor gas inventories, forecasting models, and the long-range transport of air pollutants. Although current efforts to reduce fuel emissions will lead to gradual improvements, a better understanding of the connection among particulate matter, ground-level ozone, acid deposition and hazardous air pollutants will be essential to creating effective strategies for managing these critical air quality issues simultaneously.

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