Ozone

Health Effects

In recent years, smog, a mixture of pollutants in the atmosphere has become increasingly more significant. A primary pollutant of smog, ground level ozone, is a colourless and high-irritating gas [1]. Many acute and reversible health effects have been observed following exposures to ozone lasting anywhere from 5 minutes to 6.6 hours [4]. Such effects include: increases in symptoms of respiratory discomfort (e.g. cough, shortness of breath), inflammation of lung tissue, decrease in lung capacity, increased susceptibility to respiratory illnesses such as bronchitis and pneumonia due to weakening of the body's immune system, and increases in hospital admissions [ec and American).

Both controlled human clinical studies and epidemiological studies have also found plausible links between exposure to ozone and adverse health effects [1]. For instance, a human clinical study conducted to see if low levels of ozone caused changes in inflammatory markers yielded affirmative results. While moderately exercising, healthy young men were exposed to relatively low ozone levels of 80 and 100 ppm (parts per million). Increases in lung inflammation and lung damage indicators were observed [2]. An epidemiological study conducted in Toronto from 1980-1994 also observed a correlation between ambient ozone levels and health effects. This study looked at the association between air pollution and hospital admissions for acute respiratory problems in children less than 2 years of age. Results indicated a positive association between ambient ozone levels with increased hospital admissions in the May -August period.

Epidemiological studies assessing the chronics effects of exposure to ozone indicate a decline in pulmonary function over time. Studies examining the relationship between ozone exposure and increases in mortality also have been done, however, the results are still inconclusive [4].

Susceptible Groups

Susceptible groups to the effects of ground level ozone are adults participating in increased outside activity and children. This is because the significant time spent outdoors by the two groups, increases their exposure to ozone, resulting in increased health risks. Individuals with pre-existing lung disease such as asthma and pulmonary lung disease have also been identified as a susceptible population. This results from studies indicating exposure to ozone can aggravate asthma.

Dose-Response Relationship

Rather than a threshold relationship between ozone exposure and human health, a monotonically increasing one has been observed. Lack of a threshold indicates, a level at which no adverse effects would be expected to occur due to ozone exposure can not be established. Generally, as the ozone concentration increases, so do the occurrence and severity of health effects.
National Ozone Standards

The 1-hour Canadian National Ambient Air Quality Objective for ozone is 82 ppb. Though it is known that ozone-associated adverse health effects occur below this standard level. In Canada summertime 1-hr maximum ozone levels have been recorded up to 213 ppb (ec).