DEEP: Ozone Fact Sheet

Ozone Fact Sheet

What is Ozone?

  • Ozone is an extremely reactive, colorless gas comprised of three atoms of oxygen.  Ozone exists naturally in a layer of the earth's upper atmosphere known as the stratosphere, where it shields the earth from the sun's harmful ultraviolet rays.  However, ozone found close to the earth's surface, called ground-level ozone, is a component of smog and a harmful pollutant.
  • Ground-level ozone is produced by a complex chemical reaction between volatile organic compounds (VOCs) and nitrogen oxides (NOx) in the presence of sunlight. (See: EPA: What is ozone?)
  • In addition to the natural production of VOCs from trees and other vegetation, sources of man-made VOCs and NOx include:
    • Automobiles, trucks and buses
    • Gasoline storage, transfer and refueling
    • Large combustion sources at utility and industrial facilities
    • Industrial use of solvents and degreasing agents
    • Off-road engines such as construction equipment, aircraft, locomotives, boats and lawn & garden equipment
    • Consumer products such as paints and cleaners

What are the Health and Ecological Effects of Ozone?

(See: EPA: Impacts from Ozone)
  • Exposure to ozone has been linked to a number of respiratory health effects, including significant decreases in lung function, inflammation of airways, and increased symptoms such as cough and pain when breathing deeply.
    • Children are among the most at risk from ozone exposure because their respiratory systems are still developing and they breathe more per pound of body weight than adults.  Active children often spend significant time outdoors during the summer, when ozone levels are at their highest.  Children also have a higher incidence of asthma, which may be aggravated by ozone exposure.
    • Individuals with existing respiratory diseases such as emphysema, chronic bronchitis, and asthma are also at risk because their lung function is already reduced and cannot tolerate the additional reduction caused by ozone exposure.  Aggravation of existing respiratory disease can result in increased medication use, as well as hospital admissions and emergency room visits.
    • Even healthy adults who are active outdoors (e.g., outdoor workers, joggers) respond more severely to ozone exposure than people at rest.
    • Long-term exposure to moderate levels of ozone may cause permanent lung structure changes and worsen chronic lung disease.
  • High concentrations of ozone can contribute to reductions in agricultural crop production and forest yields, as well as increased susceptibility of plants to disease, pests and other environmental stresses such as harsh weather.

When are Ozone Levels in the Air Considered to be Unhealthy?

  • The Clean Air Act requires the U.S. Environmental Protection Agency (EPA) to establish National Ambient Air Quality Standards (NAAQS) that adequately protect public health.  In 1997, EPA revised the ozone NAAQS by establishing a new, more stringent standard referred to as the 8-hour standard because measurements are averaged over an 8-hour period.
  • The previous standard, referred to as the 1-hour standard because measurements are averaged over each 1-hour period, had been in place since 1979.  The 1-hour standard was met when the expected number of days per calendar year with maximum 1-hour average concentrations above 125 parts per billion (ppb) (i.e., the 1-hour ozone design value) is equal to or less than one.
  • The current 8-hour standard is met when the 3-year average of the annual fourth highest daily maximum 8-hour average concentration (i.e., the 8-hour “design value”) is not equal to or greater than 85 ppb.
  • As part of EPA’s implementation of the 8-hour standard, the 1-hour standard was revoked as of June 15, 2005.  However, states are required to maintain control programs which were included in their state implementation plan (SIP) for the 1-hour standard.

What are the Ozone Levels in Connecticut?

  • The Connecticut Department of Energy and Environmental Protection (CT DEEP) has been measuring ambient ozone levels since the 1970’s. CT DEEP’s current monitoring network (Figure 1) includes eleven ozone monitoring sites located around the state. (See also: CT Air Monitoring Sites)
  • Typically, measured ozone levels in Connecticut exceed the NAAQS on several days each summer, depending on weather conditions.  The highest ozone levels usually occur on the hottest summer days, when the prevailing winds transport emissions that add to Connecticut’s own contribution to ozone production, as follows:
    • Surface-level winds from a southwesterly direction transport emissions from the New York City area, as well as other urban areas along the Interstate-95 corridor, into Connecticut.
    • Winds higher up in the atmosphere (at around 2000 to 5000 feet) are from the west, transporting emissions from large power plants in the Midwest into Connecticut.
  • All of Connecticut is currently classified as “nonattainment” for the 8-hour ozone NAAQS.
  • Although classified as “nonattainment,” Connecticut’s peak ozone levels have improved dramatically since 1980 as a result of numerous local, regional and national emission control strategies.  For example, Connecticut’s 1-hour ozone design values have declined from 272 ppb in 1980 to 137 ppb in 2005 (See Figure 2). A similar downward trend has occurred in the number of days when 8-hour ozone levels exceed the 8-hour standard. (See also: CT Ozone Trends)

How Can I Find Out if Ozone Levels Will be Unhealthy?

  • Ground-level ozone concentrations tend to be especially high on summer days when the weather is hot and sunny.  Each day from May through September, CT DEEP staff retrieve and review monitored ozone data and weather forecast information, and then issue ground-level ozone forecasts for the following day.
  • Whenever ozone concentrations are expected to exceed the health standard, an “Ozone Action Day” is forecasted. The forecast is made available to the public on a daily basis in the following ways.
    • 24-hour toll free Clean Air Hotline:  1-800-249-1234
    • Online at the CTDEEP’s Air Quality Index webpage: CT AQI webpage
    • Online at the US EPA’s AIRNOW website: EPA Airnow

What is Connecticut Doing to Continue to Reduce Ozone Levels?

  • Numerous local, regional and national emission control programs have been implemented over the last 25 years to produce the improvements in ozone levels described above.  Some of the ongoing ozone reduction programs include:
    • National motor vehicle emission standards for new cars and trucks (See: Vehicle Standards)
    • Reformulated gasoline (See: Reformulated Gasoline)
    • Gasoline vapor controls for bulk storage tanks, tanker trucks, underground storage tanks and dispensing pumps at gas stations
    • Vehicle emission inspection and maintenance
    • National standards for paints, consumer products and automobile refinishing
    • “Reasonably Available Control Technology” at industrial and commercial facilities
    • Increasingly stringent emission standards for power plants and municipal waste combustors
    • Phase-in of tighter emission standards for engines used in construction equipment, watercraft, locomotives, farm equipment and lawn & garden equipment
  • Several additional programs have been adopted and will be implemented over the next several years to continue progress towards achieving the ozone NAAQS.  These control programs include:
    • Requirements that vehicles sold in Connecticut meet California standards for new cars and trucks
    • Enhancements to Connecticut’s vehicle emission inspection and maintenance program
    • Requirements for additional controls at gasoline stations and automobile refinishing shops
    • Requirements for sale of gasoline cans that minimize spillage and vapor emissions
  • States with 8-hour nonattainment areas are required to develop plans (State Implementation Plans, or SIP’s) by June 2007 that include sufficient additional controls to achieve the 8-hour ozone NAAQS.  For “moderate” nonattainment areas, such as Connecticut, 8-hour NAAQS compliance is mandated to occur by June 2010.  The CT DEEP will be working with EPA and other states in the Northeast to identify and implement additional cost-effective control programs to meet that mandate.  There will be opportunity for public comment prior to adoption of any new regulations.

What Can I Do to Reduce Emissions that Cause Ozone Formation?

  • We all make decisions every day that can have an impact on the quality of the air that we must breathe.  Check out these tips for improving air quality to find out ways you can modify what you do in your car, in your yard, and around your house to minimize your contribution to high ozone levels in Connecticut.