Air parcels containing either ozone or its precursors can be transported some distance from their sources on prevailing winds, and the reactivity of the surfaces over which these air parcels travel influences the ultimate concentration of ozone at downwind sites. The episodes of elevated ozone noted in Southwestern Ontario during the summer months typically originate in the Ohio Valley of the US, and are carried northeast on the prevailing winds. Similarly, the urban emissions of the Greater Toronto Area are carried towards Lake Simcoe, and Nova Scotia and New Brunswick receive air from the metropolitan areas of New York and Boston. The formation of ozone in the biosphere is enhanced during the summer months, as elevated air temperatures and brighter sunlight shift the chemical equilibrium to favour ozone formation. Ozone is a pulmonary irritant, and has been linked to the recently noted increases in juvenile asthma and hospital admissions.
Ozone is also toxic to vegetation at concentrations which commonly occur in rural parts of Canada.
It is absorbed by the leaves of plants through stomata, following the same pathway as carbon dioxide and water vapour. OH , H 2 O 2 and O 2 - . In vitro studies of ozone and cellular molecules suggest that amino acids containing -SH groups are particularly reactive with ozone, whereas polyunsaturated fatty acids reacted far less frequently. Based on these studies, it is assumed that both free and membrane-bound proteins, such as those involved in transport or biosynthesis, may be functionally impaired by ozone fumigation. Indeed, electron micrography has indicated that one of the earliest cellular indications of ozone fumigation is swelling of chloroplasts, with consequent disruption of photosynthetic carbon fixation.