History of Ozone and Oxidant Ambient Air Quality Standards:
Adverse, Serious and Emergency

This page last reviewed November 25, 2009

In 1959, the Department of Public Health developed air quality standards for pollutants for which there were adequate data. The standards were designed to protect groups of persons who are the most sensitive to air pollution effects. In order to accomplish this, the Health Department set up three levels of standards: adverse, serious and emergency. These three levels were designed to protect the population from different levels of harmful health and environmental effects. It is important to note, however, that the 1959 standards were developed without a margin of safety. In other words, standards were set at the pollution levels identified in studies as the lowest concentrations at which harmful health effects were reported (DPH, 19591).

The following describes the three different levels of air quality standards.

"Adverse Level"

Levels of pollutants, or possible combination of pollutants, likely to lead to "untoward" symptoms or discomfort, defined the "adverse level." The staff document defined 'untoward symptoms' as symptoms which, in the absence of an obvious cause such as air pollution, might lead a person to seek medical attention and relief. Though not known to be associated with the development of disease, even in sensitive groups, effects under the "Adverse Level" were considered capable of causing populations of people to relocate away from polluted areas, a regulatory concern at that time. The "adverse" level of a pollutant was described as a level that lead to vegetation damage, reduction in visibility, or property damage of sufficient magnitude to constitute a significant economic or social burden.

"Serious Level"

Levels of pollutants, or possible combination of pollutants, likely to lead to insidious or chronic disease, or to significant alteration of important physiological function in a sensitive group, defined the "serious" level. Such an impairment of function implied a health risk for persons constituting such a sensitive group, but not necessarily for persons in good health.

"Emergency Level"

Levels of pollutants, or possible combination of pollutants, and meteorological factors likely to lead to acute sickness or death for a sensitive group of people defined the "emergency Level."



California State Department of Public Health (1959) Technical Report of California Standards for Ambient Air Quality and Motor Vehicle Exhaust.

For more information, please contact Dr. Linda Smith at (916) 327-8225

Ozone History