Effects of Ozone, Sulphates and Particulate-The Effects of Smog on the Health ofCanadians (PRB98-4e)

Smog is formed mainly above urban centres by concentrated human activities including the burning of fossil fuels. Smog is composed mainly of: tropospheric ozone, the result of a photochemical reaction between volatile organic compounds and nitrogen oxides; primary particulate matter such as pollen and dust; and secondary particulate matter such as sulphur oxides, volatile organic compounds, and ammonia gas. The scientific community is paying increasing attention to the effects of air pollution on health. Most studies are carried out on ozone, sulphates, or particulate matter.

Studies show that air pollution has indisputable effects on human health. However, scientists have thus far been unable to establish links between specific pollutants and observed diseases because pollutants scattered throughout the air often come from the same source and are released at the same time, thus forming a mixture. As well, the effects of these pollutants can be influenced by a number of factors, including individual reactions, air pollutant concentrations, pollutant types, exposure, and types and levels of individual activity, all of which are investigated in the studies.

Individuals’ health and age also influence their sensitivity to pollution. Senior citizens, people already suffering from lung problems such as asthma, and children, who spend more time outdoors and have faster heartbeats than adults, are particularly vulnerable to pollutants.(1)

Though these groups are particularly at risk, perfectly healthy adults are also sensitive to the effects of smog if they work or are active outdoors. Physical performance is lower when sustained physical effort is carried out in an urban setting at rush hour, when tailpipe emissions are high. This is because carbon dioxide (CO₂) bonds readily with the red blood corpuscles so that the oxygen supply of persons exposed to pollution is reduced.

Studies carried out to date on the effects of smog on health have used three main methodologies. Epidemiological studies use field data such as the ambient concentrations of pollutants and their actual effects on a given population. Clinical studies expose healthy, at-risk subjects, such as persons with asthma, to pollutants synthesized in the laboratory in concentrations similar to those existing in the natural environment (see table below). Toxicology studies expose animals, tissues, or human cells to pollutants synthesized in the laboratory. Three studies are described in greater detail below; the table illustrates the effects observed from applying the various methodologies.

An ozone concentration of 0.12 parts per million (ppm) is not unusual in urban centres in the summer but, according to this study, even a controlled concentration of 0.08 parts per million caused lung problems among the subjects studied. Whether or not these effects are reversible is not known. Repeated exposure to pollution does attenuate the observed effects, apparently suggesting adaptation, and scientists are studying the effects of intermittent exposure on this supposed adaptation. Other studies would have to be carried out on the public in order to assess chronic long-term effects.

According to a number of epidemiological studies, persons with asthma are, in the short term, hospitalized more often when exposed to lower concentrations of ambient ozone than cause reactions among healthy persons. Scientists are studying the effects of ozone on persons with more severe asthma and persons with allergies.

In the short term, ozone causes irritations and symptoms including coughing and painful breathing.

Study	Methodology	Pollutants	Subjects	Effects on Health	Comments
Study No.1	Review of clinical and epidemiological studies, 1978-1993	Ozone	Healthy adults and children	Reduced respiratory functions Increased reactivity of respiratory passages Lung inflammation Increased respiratory symptoms	Effects increase with exercise. Ozone is more harmful than sulphates. Effects seem to be combined with those of acid aerosols and particulate matter.
			Athletes and persons working outside	Reduced exercise capacity
			Persons with asthma	Increased hospitalizations
Study No.1	Review of clinical and epidemiological studies	Sulphates (sulphur dioxide)(PM₁₀)	Persons exposed to ambient concentrations of between 30 and 150 µ m/m³		Effects occur at indoor ambient concentrations if there are unventilated sources of combustion.
			Healthy adults	Increased reactivity of respiratory passages
			Persons with asthma	Reduced respiratory functions
			Children	Increased respiratory symptoms and infections
Study No.2	Epidemiological study: regression statistics	Ozone, sulphates	Urban air concentrations between May and August	Increased hospitalizations for respiratory illnesses such as asthma, infections, and chronic obstruction of respiratory passages	Ozone is more harmful than sulphates. There is a correlation between temperature and mixture of ozone and sulphates. sulphates’ effect is intensified by an excess of positive ions in the air.
Study No.3	Review	Particulate sulphates		Increased hospitalizations for cardiovascular and respiratory illnesses Increased respiratory symptoms Reduced respiratory functions Links between airborne particulate matter and premature deaths attributable to cardio-pulmonary and respiratory illness

Source: Anonymous, "Health Effects of Outdoor Air Pollution," American Journal of Respiratory and Critical Care Medicine, Volume 153, 1996; The Acidifying Emissions Task Group, Towards a National Acid Rain Strategy, presentation to the National Air Issues Co-ordinating Committee (NAICC).

This study was carried out in 168 hospital emergency rooms in Ontario. It shows a significant positive correlation between hospitalizations for respiratory illnesses and concentrations of ozone and sulphur in the air. The presence of these substances was noted on the day of, and up to three days before, admissions to hospital, from May toAugust and from 1983 to 1988. Of hospitalizations, 5% were linked to the concentration of ozone and 1% to the concentration of sulphates. Ozone was seen to have a greater influence on hospitalizations than sulphates. Causes of hospitalization were asthma, chronic illnesses obstructing the respiratory passages, and infections. These findings applied to all age groups; children suffered most from a mixture of ozone and sulphates, accounting for 15% of hospitalizations, while senior citizens suffered least. The study was carried out in a circular area, 1,000 kilometres across, with 8.7 million inhabitants. With respect to the possible influence of other factors on the link between hospitalizations and ozone and sulphate concentrations, temperature seems to have an effect, but relative humidity and air pressure apparently do not. Where pollutants are concerned, an excess of positive ions in the air seems to influence sulphate concentration. Other studies show a correlation between sulphate concentration and particulate matter in the air.

A number of studies link particulate sulphates with increases in premature deaths, hospitalizations, asthma symptoms, bronchitis and other respiratory illnesses. Senior citizens and persons with existing cardiovascular and respiratory illnesses appear to be more sensitive than the rest of the population.

Some scientists link these effects with fine particulate matter, measuring 2.5 microns in diameter or less (PM_2,5); others, with particulate matter combined with other pollutants such as ozone, sulphur dioxide, and metals.(5) The studies on particulate sulphates state that, even at ambient concentrations of between 30 and 150 microns per cubic metre, these pollutants are linked with increased fatal cardiovascular attacks, particularly when combined with high-risk activities such as smoking. These pollutants are also linked to child hospitalizations, school absences, and increased use of medication by asthmatics.

The effects on health can be chronic or acute. Chronic illnesses include permanent degeneration of respiratory functions, new cases of bronchitis, and increased deaths linked to sustained exposure to air pollution. Acute effects include temporary changes in respiratory functions, more hospitalizations for cardio-pulmonary attacks, and more deaths linked to short episodes of high pollution.(6) The studies also observed other health problems such as aggravated respiratory infections, asthma, emphysema, coronary pathology, and lung cancer.

Although scientists have thus far been unable to establish precise links between specific types of particulate matter and particular effects, these studies show that exposure to these air pollutants increases the frequency of cardiovascular and respiratory illnesses and mortality.

(6) Richard T. Burnett, et al., "Association between Ozone and Hospitalization for Respiratory Diseases in 16 Canadian Cities," Environmental Research, Vol. 72, 1996, p. 24-31.