History of Ozone and Oxidant Ambient Air Quality Standards

This page last reviewed May 6, 2005

This site describes the history of the ambient air quality standards for ozone and oxidant air pollutants in California. Click on dates below, or scroll down, to find more detailed information on the history of the ozone ambient air quality standards.

History of Ozone and Oxidant Ambient Air Quality Standards

Year	Pollutant	Concentration (parts per million)	Averaging Time	Notes
1955	Oxidant	0.5 ppm	1 hour	First of Three Alert Stage - Developed for Los Angeles Air Pollution Control District
1959	Oxidant	0.15 ppm	1 hour	First Statewide Oxidant Standard - Set at the lowest concentration at which eye irritation, vegetative damage and visibility reduction have been reported.
1969	Oxidant	0.1 ppm	1 hour	Standard set to prevent or abate the following effects: eye irritation and possible impairment of lung function in persons with chronic pulmonary disease.
1970	Oxidant	0.10 ppm	1 hour	Standard level set to prevent the aggravation of respiratory diseases and to prevent or abate eye irritation.
1975	Oxidant as Ozone	0.10* ppm	1 hour	Standard level set to prevent the aggravation of respiratory diseases.
1988	Ozone	0.09* ppm	1 hour	Standard set to prevent aggravation of respiratory diseases.
2005**	Ozone	0.09* ppm	1 hour	Standard set to prevent the following short-term health effects: One-Hour and Multi-Hour Exposures - Lung Function Decrements and Symptoms of Respiratory Irritation and Multi-Hour Exposures - Airway Hyperreactivity and Airway Inflammation.
		0.070* ppm	8 hour

*	Defined the highest level of ozone that can be present without adverse health effects.
**	These concentrations were approved by the Air Resources Board on April 28, 2005 and are expected to become effective in early 2006.

Background

The Air Resources Board (ARB) and previous health agencies have been involved in setting ambient air quality standards since the 1950's. In the early years, California agencies set standards for "oxidant," a term describing a mixture of known and unknown oxidizing air pollutants. As new scientific information emerged over the years, it became clear that ozone was the primary cause of respiratory health effects within the oxidant class.

The first ambient (outdoor) air quality standard in California was set in the Los Angeles area because of the severity of smog there. The Los Angeles Air Pollution Control District adopted a three-stage alert system for "oxidants" and three other pollutants in June of 1955. This system was designed to prevent the possibility of an air pollution catastrophe. In 1959, the State Legislature authorized the Department of Public Health (DPH) to set statewide ambient air standards for California. During the same year DPH adopted standards for six air pollutants, including a one hour oxidant standard of 0.15 parts per million (ppm).

The Air Resources Board (ARB) was formed in 1967 and assumed the responsibility of setting ambient air quality standards for oxidant and other air pollutants. Over successive years, the ARB adopted increasingly health protective standards for oxidant, and then ozone. In 1969, the ARB adopted a one-hour oxidant standard of 0.1 ppm, but revised it to 0.10 ppm the following year, adding a decimal place. This change allowed for a more health protective standard. Also in 1970, the ARB analyzed available data and determined that the then existing oxidant standard was below the threshold associated with aggravation of respiratory disease, establishing the standard at a level below which the principal health effects would occur. In 1975, ARB set a standard specifically for ozone (instead of total oxidant), using the ultraviolet photometry chemical analysis method which is specific for ozone. In 1988, ARB reduced the level of the standard to 0.09 ppm.

In the years before the ARB was formed, an ambient air quality standard was set without a margin of safety. In other words, an air quality standard was set at the lowest concentration of a pollutant at which harmful health effects had been observed and reported (DPH, 1959¹). In the present day, air quality standards define clean air, and represent the maximum amount of a pollutant that can be present in outdoor air without harm to the public's health. Air quality standards are designed to provide a margin of safety for the most sensitive members of the public.

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

1955

In June of 1955, the Los Angeles Air Pollution Control District established a three-stage smog alert system for four air pollutants, including ozone. This system was designed to prevent a possible air pollution disaster in Los Angeles County. Oxidant concentrations are presented in parts per million (ppm) in air.

Three Stage Alert System¹ for Oxidant (1955)
First Alert (Relatively Safe)	Second Alert (Harmful)	Third Alert (Dangerous)
0.5 ppm²	1.0 ppm	1.5 ppm

1.	Rule 156, VII. Los Angeles Air Pollution Control District; an alert was called if the oxidant level reached the indicated concentration.
2.	Oxidant concentrations were averaged over one hour.

1959

In 1959, the Department of Public Health developed and published statewide air quality standards for California, as instructed by the State Legislature (Assembly Bill 1386).

On December 4 of that year, the State Department of Public Health's Advisory Committee on Air Sanitation set the first ambient air quality standards for California. The Health Department established three levels of standards: Adverse, Serious and Emergency. While state air quality standards for other pollutants were set for all three levels, the oxidant standard was established for only the adverse level.

Oxidant¹ Index at the Adverse Level²(1959)
Concentration of Oxidant	Averaging Period	Method of Analysis	Bases for the Standard³
0.15 ppm	1 hour	Potassium Iodide	Eye Irritation, Vegetative Damage and Visibility Reduction

1.	Oxidant - At the time of adoption of this standard, "oxidant" was thought to include ozone, nitrogen dioxide, hydrocarbons, photochemical aerosols and possible other unknown oxidants.
2.	Adverse Level - ARB defined the "Adverse Level" as the concentration of an air pollutant likely to lead to 'untoward symptoms' or discomfort such as eye irritation. 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.
	Also in the adverse level category were levels of pollutants that lead to costly and undesirable effects other than those in humans. These included damage to vegetation, reduction in visibility, or property damage of sufficient magnitude to constitute a significant economic or social burden.
3.	Bases for the Standard: The terminology, "Bases for the Standard" referred to the health and environmental effects which began to appear at the level of the standard.
	In 1959, there were not enough high quality health effect studies to set standards at the "Serious" and "Emergency" levels for the individual components of "oxidant" (ozone, nitrogen dioxide, hydrocarbons and "photochemical aerosols"). The Department of Public Health published notes on several compounds thought to be included in the mixture termed "oxidant," citing studies and papers which presented the most up-to-date health effects data at that time. The following paragraphs describe the documented health effects for the individual components of "oxidants."
	Ozone, at 1 ppm for eight hours daily for about a year, induced bronchiolitis and fibrositis in rodents (Stokinger, H.E., Wagner, W.D., and Dobrogorski, O.J., A.M.A. Archives of Industrial Health 16: 514m 1957). Extrapolation of these data to man is difficult. Functional impairment data were reported by Clamann and Bancroft (Clamann, H. G. and Bancroft, R.W., Advances in Chemistry, No. 21, pp.352-359); at 1.25 ppm some effect was observed on residual volume and diffusing capacity. The variability of the tests was not reported. Additional data would be needed before a standard is set.
	A value of 2.0 ppm of ozone for one hour might produce serious interference with lung function in healthy persons, and the assumption was made that this potential health effect might cause acute respiratory illness in sensitive persons. (Clamann, H. G., op. cit.)
	Five ppm of nitrogen dioxide for eight hours induced decreased pulmonary function in animals. Slightly more might produce pulmonary fibrosis (Stokinger, personal communication); nitrogen dioxide from air pollution exposures is usually combined with nitric oxide and ozone. More data on human exposures would be needed prior to setting a standard.
	Hydrocarbons are a group of substances most of which, normally, are toxic only at concentrations in the order of several hundred parts per million. However, a number of hydrocarbons can react photochemically at very low concentrations to produce irritating and toxic substances. Because of the large number of hydrocarbons involved, the complexity of the photochemical reactions, and the reactivity of other compounds such as nitrogen dioxide and ozone, it was not considered possible to establish "serious" and "emergency" levels for hydrocarbons at that time. The standard document stated that, from the public health standpoint, the concentration of these hydrocarbons which react photochemically should be maintained at or below the level associated with the oxidant index defined in the "adverse" standard.

1967

The Mulford-Carrell Act established the Air Resources Board (ARB), and authorized the agency to set air quality standards for the state of California. The Act also directed the ARB to establish regional air quality basins.

1969

On September 17, 1969, ARB adopted a stricter, more health-protective one-hour standard for "oxidant," redefining the term to be "oxidant including ozone." The term "Most Relevant Effects" referred to the health effects which the standard was intended to prevent or abate.

Oxidant Including Ozone¹ (1969)
Concentration	Averaging Period	Method	Most Relevant Effects
0.1 ppm²	1 hour	Potassium Iodide	Eye Irritation; Possible impairment of lung function in persons with chronic pulmonary disease³.

1.	At that time, the group of compounds included in the "oxidant" group were thought to include ozone, peroxides and peroxyacyl nitrates, but not nitrogen dioxide (see NO₂ Standard and History). A correction factor was added for the measurement of nitrogen dioxide.
2.	The standard was said to be exceeded in an air basin when 0.1 ppm or more of oxidant, including ozone, occurs seven (7) or more days in 90 consecutive days or three (3) or more consecutive days.
3.	Most Relevant Health Effects to be Prevented or Abated included eye irritation and possible impairment of lung function in persons with chronic pulmonary disease. At that time, these effects were thought to be associated in some way with the presence of ozone in the atmosphere, but not necessarily directly caused by it.

1970

On November 19, 1970, ARB adopted revisions to the Table of Standards. ARB retained the one-hour 0.1 ppm ozone standard but altered statements about health effects and the ozone levels that would violate the standard.

Oxidant Including Ozone (1970)
Concentration	Averaging Period	Method	Most Relevant Effects
0.10 ppm¹	1 hour	Potassium Iodide	Eye Irritation^2,3

1.	The ambient ozone air quality standard is said to be violated when the average hourly ozone concentration exceeds 0.1 ppm, without reference to frequency or duration of occurrence. The following statement was removed, "Ozone standard said to be exceeded when 0.1 ppm or more of oxidant, including ozone, occurs seven days (7) or more in any 90 consecutive days or for three (3) or more consecutive days."
2.	Most Relevant Effects to be Prevented or Abated - The term, "Most Relevant Effects" refers to the health effects which the standard was intended to prevent. Although the level of the standard was then associated with eye irritation, the 0.1 ppm hourly standard was considered to be below the concentration associated with aggravation of respiratory diseases.
3.	The statement, "Possible impairment of lung function in persons with chronic pulmonary disease" was removed under the "Most Relevant Effects column."

1971

In 1971, the US EPA established a national air quality standard of 0.08 ppm for ozone, as required by 1970 amendments to the federal Clean Air Act.

The federal standard specified the chemiluminescent method of analysis, which was reported to be specific for ozone¹. At that time in California, the "oxidant" ambient air quality standard of 0.10 ppm used the relatively nonspecific potassium iodide method. In a staff report dated March 15, 1972, the ARB and the State Health Department determined that neither method was sufficiently sensitive or accurate enough to distinguish measured results from one another. Thus, there was insufficient reason to change ARB's air quality standard for oxidant.

1.	Note that the U.S. EPA's chemiluminescent method of analysis for ozone or oxidant used a version of the potassium iodide method (however, not the ARB version) to calibrate and help verify the accuracy of results.

1975

On May 15, 1975, the ARB adopted revisions to the one-hour ozone standard, defining "oxidant" as ozone, and changing the measurement method.

Oxidant as Ozone (1975)
Concentration	Averaging Period	Method	Most Relevant Effects¹
0.10 ppm	1 hour	Ultraviolet Photometry²	Aggravation of Respiratory Diseases

1.	Most Relevant Effects to be Prevented - This level was considered to be below that associated with aggravation of respiratory diseases.
2.	ARB substituted the ultraviolet photometry method for the neutral buffered potassium iodide method. The new method is specific for measuring ozone and was considered superior to the former method.

1988

On May 24,1988, the ARB adopted a stricter, more health-protective one-hour ozone standard. The air quality standard now refers to ozone, and not "oxidant."

Ozone (1988)
Concentration	Averaging Period	Method	Most Relevant Effects
0.09 ppm¹	1 hour	Ultraviolet Photometry	See Footnote #2

1.	These standards are violated when concentrations exceed those set forth in the body of the regulation.
2.	Most Relevant Effects to be Prevented Include:
	a.	Short-Term Exposures Pulmonary function decrements and localized lung edema in humans and animals. A risk to public health from ozone exposure is implied by alterations in pulmonary morphology and host defense in animals.
	b.	Long-Term Exposures Risk to public health implied by altered connective tissue metabolism and altered pulmonary morphology in animals after long-term exposures and pulmonary function decrements in chronically exposed humans.
	c.	Welfare Effects Yield loss in important crops and predicted economic loss to growers and consumers. Injury and damage to native plants and potential changes in species diversity and number. Damage to rubber and elastomers and to paints, fabric, dyes, pigments, and plastics.
	d.	Comments The standard is intended to prevent adverse health effects. The standard, when achieved, will not prevent all injury to crops and other types of vegetation, but was intended to place an acceptable upper limit on the amount of yield and economic loss, as well as on adverse environmental impacts.

1999

In 1999, the California Legislature adopted the Children's Environmental Health Protection Act.

This Act required an evaluation of California's ambient air quality standards to determine whether they adequately protect public health, including that of infants and children, with an adequate margin of safety. Staff of the ARB and the Office of Environmental Health Hazard Assessment (OEHHA) were directed to evaluate and prioritize for review existing California standards. Those air quality standards found possibly inadequate would undergo full review and possible revision.

From the evaluation mandated by the Children's Environmental Health Protection Act, staff scientists of ARB and OEHHA published a December 2000 report, concluding that significant harmful health effects might occur among both children and adults when outdoor ozone concentrations are at or near the current (1988) State standard. Staff gave ozone a high priority for comprehensive review of available health data.

2005

Staff scientists at the ARB and OEHHA evaluated the available scientific information on the health effects, atmospheric chemistry, public exposure levels and welfare effects of ozone. From this evaluation, staff developed recommendations which are designed to adequately protect public health, including that of infants and children. These recommendations were approved by the Air Resources Board at its April 28 meeting and are expected to become effective in 2006.

Draft Recommendations for Ozone (2005)
Concentration¹	Averaging Period	Method²	Most Relevant Effects
0.09 ppm*	1 hour	Ultraviolet Photometry	See Footnote #3
0.070 ppm*	8 hours	Ultraviolet Photometry	See Footnote #3

* Recommended ambient air quality standards for ozone.

1.	These levels are not to be exceeded.
2.	Staff recommended that the ultraviolet photometry method of analysis be retained and to incorporate all federally approved ultraviolet methods as California Approved Samplers for ozone see list of methods at:
	US EPA, Ambient Monitoring Technology Information Center (AMTIC) Air Monitoring Methods - Criteria Pollutants
3.	Most Relevant Effects to be Prevented Include:
	a.	Short-Term Exposures One-Hour and Multi-Hour Exposures - Lung Function Decrements and Symptoms of Respiratory Irritation Such as Cough, Wheeze and Pain Upon Deep Inspiration Multi-Hour Exposures - Airway Hyperreactivity and Airway Inflammation
	b.	Long-Term Exposures Ozone can induce tissue changes in the respiratory tract and is associated with decreased lung function, respiratory symptoms, hospitalization for cardiopulmonary causes and emergency room visits for asthma.
	c.	Welfare Effects Yield loss in important crops and predicted economic loss to growers and consumers. Injury and Damage to Forests
	d.	Comments The standard is intended to prevent adverse human health effects. The standard, when achieved will not prevent all injury to crops and other types of vegetation, but is intended to place an acceptable upper limit on the amount of yield and economic loss, as well as on adverse environmental impacts.