Ozone - April through September

Ozone is a colorless, odorless gas that occurs naturally in the upper atmospheres where it absorbs harmful ultraviolet rays. But at ground level, ozone is created when sunlight and heat cause chemical reactions between volatile organic carbon particles and nitrogen oxide particles. Because ozone is formed with sunlight and heat, concentrations may reach unhealthy levels on warm, sunny days.

The new ozone standard (0.080 ppm) set by the Environmental Protection Agency (EPA) is for an 8-hour exposure. The more stringent eight-hour standard provides a more realistic exposure to harmful health effects of ground-level ozone pollution. The standard is based on medical studies indicating that prolonged exposure to low-level ozone concentrations is as harmful to human health as exposure to higher levels for shorter durations.

When we are close to an exceedance of that standard a High Pollution Advisory (HPA) will be issued by the Arizona Department of Environmental Quality (ADEQ). These advisories alert Valley residents and businesses to reduce driving and encourage other behavior changes to help prevent an ozone exceedance.

Ozone Health Watches will be issued when air quality is considered unhealthy for sensitive population groups: children, seniors, and people with respiratory ailments.

It is important to participate in trip reduction so that we do not reach exceedance levels.

Ozone PowerPoint Presentation

Sources of Ozone - Maricopa County, 1995

Ground-level ozone is formed by a chemical reaction between volatile organic compounds (VOCs) and oxides of nitrogen (NOx) in the presence of sunlight. Sources of VOCs and oxides of nitrogen include:

• Automobiles, trucks, and buses.



• Large industry and combustion sources such as utilities.



• Small industry such as gasoline dispensing facilities and print shops.



• Consumer products such as paints and cleaners.



• Nonroad engines such as aircraft, locomotives, construction equipment, and lawn and garden equipment.



• Ozone concentrations can reach unhealthy levels when the weather is hot and sunny with relatively light winds.

Current Situation

For ozone, EPA determined in May 2001 that the Valley has attained the federal 1-hour ozone standard, as no violations of the standard have occurred since 1997. The new 8-hour ozone standard means that additional effort will be needed to avoid exceedances. ADEQ has adopted strategies to help keep Maricopa County from reaching unhealthy ozone levels.

What Strategies are in Place to Reduce Ozone?

• Cleaner burning gasoline is sold in the Phoenix-metro area during the summer months.



• Vapor recovery systems control emissions of gasoline vapors when you fill your gas tank.



• Enhanced Vehicle Emissions Testing Program - I/M147.



• Voluntary Vehicle Repair and Retrofit Program provides for the installation of an emission upgrade kit designed to reduce exhaust emissions.



• The Clean Air Program is a public education and marketing campaign that encourages the use of alternative forms of transportation and other pollution reducing strategies.



• Maricopa County's Trip Reduction Program requires Valley employers with 50 or more employees to encourage their employees not to drive to work alone.

Find out how you can help to reduce pollution in the Valley.

Ozone can be harmful to the public. Please visit Health Effects of Ozone to learn more about the health risks of exposure to ozone pollution.