Ozone Insight

What is Ozone?

Ozone is a molecule composed of three atoms of oxygen, designated by the chemical symbol O. It is created naturally by lightning and by solar ultraviolet rays in the upper atmosphere. It is also generated by photochemical reactions between air pollutants in urban and industrial areas. Ozone is a virtually colourless gas with a characteristic acrid odour. It is slightly soluble in cold water. Ozone is strongly oxidising and can be used as a deodorising and bleaching agent. At very low levels, it can make the air smell fresh (eg after lightning). At higher levels it can be harmful to human health.

How can ozone be harmful?

• Decreases in lung function
  
• Aggravation of asthma
  
• Throat irritation and cough
  
• Chest pain and shortness of breath
  
• Inflammation of lung tissue
  
• Higher susceptibility to respiratory infection
  

Even low concentrations of ozone can be harmful to the upper respiratory tract and the lungs. The severity of injury depends on both by the concentration of ozone and the duration of exposure. Severe and permanent lung injury or death could result from even a very short-term exposure to relatively low concentrations.

Exposure to extremely low concentrations of ozone initially increases the reactivity of the airways to other inhaled substances (bronchial hyper responsiveness) and causes an inflammatory response in the respiratory tissue. Exposure to ozone during exercise or work increases susceptibility to this effect. Increased bronchial responsiveness has been observed following 7-hour exposures to 0.08, 0.1 or 0.12 ppm (with moderate exercise), or a 1-hour exposure to 0.35 ppm. This response occurs almost immediately following exposure to ozone and persists for at least 18 hours.

Other symptoms observed following acute exposures to 0.25-0.75 ppm include cough, shortness of breath, tightness of the chest, a feeling of an inability to breathe (dyspnea), dry throat, wheezing, headache and nausea.

More severe symptoms have been seen following exposure to higher concentrations (greater than 1 ppm) and have included reduced lung function, extreme fatigue, dizziness, inability to sleep and to concentrate and a bluish discolouration of the skin (cyanosis). Ozone concentrations greater than 2 ppm can be irritating to the eyes within minutes. Intermittent exposure to 9 ppm for 3-14 days has produced inflammation of the bronchi and lungs.

An acute occupational exposure to approximately 11 ppm for 15 minutes caused severe respiratory irritation and almost caused unconsciousness. A 30-minute exposure to 50 ppm is considered potentially lethal.
                                    - Canadian Centre for Occupational Health and Safety