A Historical Overview of the Ozone Exposure Problem

Ozone can be found in essentially all locations in the troposphere. Too much exposure of vegetation and humans to this potent oxidizing gas can prove toxic. Reports of human toxicity to ozone first appeared in the 1800's from accidental occupational exposures when ozone was first discovered. Ozone was recognized as damaging field vegetation with a report of altered leaf morphology in grapes in the 1950s. Ozone is the major oxidant component in photochemical smog, and is produced by reactions of volatile organic compounds and oxides of nitrogen with sunlight present. Soon after the inception of the U.S. Environmental Protection Agency (US EPA), the Agency set a general “oxidants” standard (which included ozone) in 1971. A primary standard was created to protect human health and a secondary standard to protect against agricultural losses, ecological damage, and other losses. Ozone concentrations have decreased steadily over the last two decades in some areas of the U.S., but have increased in other areas. Several aspects of ozone exposure need further characterization, including better determination of rural concentrations and the relationship of outdoor to indoor concentrations. Ozone is one of the six criteria air pollutants requiring a formal reexamination of the new findings of effects on health and vegetation on a periodic basis, a process that leads to the publication of an US EPA criteria document. As a result of further study concerning ozone effects, significant changes were made to pollution standards in 1979 and 1997. This toxicant has remained a major air pollutant of concern in the U.S. despite regulation and intense study over several decades.