Ozone is a colorless gas that is a major constituent of smog. This pollutant alone contributes to the majority of unhealthy air quality days in CT, as measured by the Air Quality Index (AQI). Ozone is found both at high altitude and ground level. High altitude ozone is beneficial because it shields the earth from the sun's ultraviolet radiation. Ground level ozone is harmful because it reacts with the mucus membranes of the respiratory system and causes inflammation.

Ozone forms in the air from other pollutants: volatile organic compounds (VOCs) and nitrogen oxides (NO and NO2) in the presence of ultraviolet (UV) radiation. Ozone does not come directly from any source. The VOCs that form ozone come from vehicle and industrial exhaust as well as evaporation of gasoline, solvents and paints, and even natural sources.

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.

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.

Related Links:

Annual Summary of Ozone Monitoring Data

Air Quality Trends - Ozone

EPA Analysis of National and Regional Ozone Trends

Ozone Planning Efforts

Daily Air Quality Index

Content last updated on May 13, 2019