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EPA's Air Quality Standards on Ozone


The ozone air quality standards were revised by the U.S. Environmental Protection Agency (EPA) in October 2015.

  • Primary air quality standards are set by the EPA to protect human health.
  • Secondary standards are set by the EPA to protect the environment.
  • The final ozone standards, both primary and secondary, were set at 70 parts per billion (or 0.070 ppm). 
  • The previous ozone standard established in 2008 was 75 parts per billion ppb (or 0.075 ppm).

Approximately every five years, the Clean Air Scientific Advisory Committee reviews new health and environmental data on a specified pollutant. After the review, the committee makes recommendations to the EPA Administrator on whether the existing standards are acceptable, or revisions should be considered. This is done to ensure that human health and the environment continue to be protected based upon the most recent scientific data. In April 2018, the EPA determined that Pima County meets the standards based on 2014, 2015 and 2016 data. Should Pima County not meet the standards, PAG, in cooperation with local, state and federal officials would develop an areawide plan and include these additional measures: 

  • Conduct a County baseline emissions inventory
  • Perform periodic inventory updates
  • Meet new industrial permitting requirements
  • Comply with the standards within three years if Pima County is classified as a marginal nonattainment area. Places that are classified with a more severe nonattainment status will be allowed more time to meet the standards.

What is ground-level ozone and how does it affect human health?

  • Ground-level ozone (GLO) is a harmful pollutant and is a major component of smog.
  • GLO is not the ozone layer, which is an invisible gas that occurs naturally in the upper atmosphere and protects the earth by filtering out harmful ultraviolet radiation.
  • GLO can damage lung tissue and make people more susceptible to respiratory infections. It is a severe lung irritant at high levels and can cause shortness of breath, coughing, wheezing and stinging eyes.
  • GLO is especially harmful to children, the elderly and those with impaired health. High ozone levels can inhibit plant growth and can cause damage to crops and forests.
  • GLO is not produced directly but is the result of complex reactions involving sunlight and chemical precursors (oxides of nitrogen and volatile organic compounds). These precursors originate from sources such as motor vehicle exhaust and industry emissions. They are also produced by local plants and soils (biogenics). In 2017, the Pima County Department of Environmental Quality commissioned an ozone precursor inventory to determine the local sources of ozone precursors. The results are shown below:


View the PDEQ report.

What is PAG’s role?

  • PAG is the designated air quality planning agency for Pima County.
  • PAG addresses air quality issues to meet federal, state and local requirements.

Who must comply with the EPA’s ozone standards and when?

All states must comply with the new ozone standards as well as with the other national ambient air quality standards (NAAQS) for carbon monoxide, particulate matter, lead, nitrogen dioxide and sulfur dioxide. Depending on an area’s level of nonattainment (marginal to extreme), states will be required to meet the standards over the April 2021 and 2038 period.

What programs help to curb ozone levels?

PAG has many programs in place to reduce vehicle emissions, a major source of the chemicals that combine to form ozone:

Regional Transportation Authority Plan and Special Taxing District. The RTA's 20-year plan (FY 2007-2026), which is funded by a half-cent exise tax of the RTA's special taxing district within Pima County, has delivered a variety of projects and services that help reduce congestion and improve traffic mobility. These include: expanded transit services, including the Sun Link streetcar, new greenways and bike paths/lanes, new sidewalk connections, improved intersections to reduce idling and new roadways that shorten drive time.

Transportation Planning. PAG is the regional transportation planning agency for the Tucson region and develops long-range and short-range transportation plans which are designed to reduce vehicle emissions by:

  • Evaluating potential road projects for congestion relief benefits. Free-flowing traffic reduces idling and fuel use, and lowers air pollution emissions.
  • PAG manages a program to coordinate the review and retiming of traffic signals throughout the region on a regular basis. Signal timing improvements reduce stops and idling traffic, resulting in less fuel consumption and emission.

Tucson Clean Cities. This is a voluntary program of the U.S. Department of Energy to advance the nation's economic, environmental and energy security by:

  • Supporting local actions to reduce the reliance of foreign sources of petroleum in transportation.
  • Promoting the use of alternative-fuel vehicles and fuels.
  • Building a local refueling infrastructure for these vehicles.

Sun Rideshare. This is a regional commuter assistance program that promotes the use of transportation alternatives, such as carpooling and riding the bus.

Travel Reduction Program. This is an employer assistance program for commuters:

  • Emphasizes reducing congestion and improving air quality.
  • Promotes the use of alternative transportation for daily trips to reduce pollution, energy consumption and traffic congestion in the region.

Bicycle and Pedestrian Planning. PAG brings together diverse groups, interests and jurisdictions in order to improve bicycle and pedestrian facilities.

Will the 2015 ozone standards impact the business community?

The business community and economic development will not be impacted by the 2015 ozone standards as long as Pima County remains an attainment area.

Has Pima County been in nonattainment before?

Yes. Pima County’s carbon monoxide levels exceeded the health standards in the 1980s. PAG developed a State Implementation Plan that established programs to reduce emissions to bring the region into attainment. These ongoing programs, which also help to reduce ozone precursor emissions, include:

  • Establishment of a vehicle inspection program
  • Sale of specialized gasoline during winter months
  • Creation of a regional Travel Reduction and Rideshare Program and PDEQ educational outreach program

Will federal regulations play a role in attaining the 2015 ozone standards?

Yes. According to the EPA’s estimates, some precursor emissions will be reduced by existing or pending federal regulations that control the following:

  • Vehicle emissions
  • Pollutants affecting visibility
  • Industrial and vehicle greenhouse gas emissions

What additional measures have other areas taken to control ozone?

Maricopa County has been an ozone nonattainment area for several years for not meeting prior ozone standards. Maricopa County’s measures to control ozone levels include the following:

  • A more stringent vehicle emissions inspection program
  • Exclusive sale of cleaner-burning gas during the ozone season
  • Non-road vehicle emission standards
  • Tougher enforcement of registration and vehicle inspection programs 

What can individuals do to help keep our air healthy?

Since vehicle emissions are a major contributor to the chemicals that combine to form ozone, individuals can:

  • Drive less
  • Ride the bus
  • Ride a bicycle
  • Walk
  • Carpool

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