Ground Level Ozone (O3)


Ozone (O3) is a highly reactive gas molecule formed of three oxygen atoms.  It forms in the Earth’s atmosphere in two different places:

  • in the high atmosphere 6–30 miles above the Earth’s surface (stratosphere) where it protects the Earth, and
  • in the atmosphere at ground level (troposphere) where it is a dangerous toxic.

In the stratosphere it forms naturally when ultraviolet radiation from the sun reacts with oxygen in its regular molecular form (O2).  Stratospheric ozone is beneficial and protects life on earth because it becomes a layer through which 97–99% of the harmful ultraviolet light from the sun cannot pass.  Without this stratospheric ozone layer, life on the earth as we know it could not exist.

In the atmosphere at ground level, Ozone is not pollution that is emitted directly, but forms in chemical reactions between pollutants called nitrogen oxides (NOx) and volatile organic compounds (VOCs).  Typically this chemical reaction takes place in the presence of sunlight and heat especially during the months of summer, but the same reactions have been observed also in cold, winter conditions in high elevation surface locations.  At ground level, Ozone is a dangerous toxic and is the principle component of smog.  Ozone also acts as a greenhouse gas in the troposphere, contributing to regional climate warming to varying degrees based on the local concentration.


 Ozone in the atmosphere (click image to view)

Ozone Health Effects

Ground level ozone can cause serious health problems such as:

  • Making it difficult to breathe deeply.
  • Coughing and sore throat.
  • Shortness of breath.
  • Lung diseases such as asthma, and emphysema.
  • Inflammation and damage of airways.
  • Eye irritation.
  • Headaches.

Ecosystem Effects

Ground level ozone can cause harmful effects on vegetation and the ecosystem. Some of these negative effects are the following:

  • Interference  with the ability of plants to produce  and store food.
  • Loss of species diversity.
  • Reduction in tree growth.
  • Damage on trees’ leaves, harming appearance of vegetation.
  • Change in water and nutrient cycles.

Ozone Reduction Rates

How can Ground Level Ozone be reduced?

  • Keeping your vehicle well tuned.
  • Avoiding idling your motor vehicle excessively.
  • Conserving energy and recycling.
  • Limit driving; carpool, walk, or ride a bicycle.
  • Using public transportation.