Knowledge Center

Ozone is a highly toxic and colorless gas, characterized by a strong odor. Ozone can be found in two layers of the atmosphere: approximately 25km above the surface of the earth (stratosphere) and at the lowest atmospheric layer (troposphere), in which we live. The ozone in the stratosphere protects us from ultra-violet radiation. Conversely, at ground level, ozone is known for its harmful effects on our health.

Ground level (troposphere) ozone is formed when polluted air, especially volatile organic compounds (VOCs) and NOx (a mix of nitric oxide, NO, and nitrogen dioxide, NO2) from traffic and manufacturing operations, interact with sunlight and high temperatures. In large quantities, it becomes smog. Emissions from industrial facilities and electric utilities, motor vehicle exhaust, gasoline vapors, and chemical solvents are some of the major sources of NOx and VOC (1).

Exposure to ground-level ozone can cause various health problems, including chest pains, coughing, congestion, and throat and eye irritation. It can worsen respiratory diseases like bronchitis, asthma, and pneumonia. There is also a growing body of evidence linking exposure to ozone and accelerated development of different malignant tumors (1).

Ozone also adversely affects eco-systems and crops by reducing production and increasing susceptibility to diseases, pests and extreme climate conditions.  

Researchers from the University of Southern California have shown that exposure to ozone may cause asthma. According to this research, healthy children practicing at least three outdoor sports in areas with high ozone concentrations were more than three times as likely to develop asthma than children who were not engaged in sports (2). This asthma risk was not found in children living in areas with low ozone concentrations. Physical activity increases breathing rate, bringing ozone into the body and worsening its hazardous health effects. Studies on animals show that breathing ozone into the body can cause morphological changes in the respiratory system.

Studies worldwide have found that ozone levels are higher during the weekend, even though that’s when there are lower levels of car emissions. This phenomenon is known as the "ozone weekend effect." The formation of ozone depends on a chemical balance between the pollutant emission rate and pollutant decomposition rate in the atmosphere. Researchers found that although small reductions in NOx may increase ozone levels, larger  reductions of NOx emissions will change the chemical balance leading to the formation of ozone, thus reducing its concentrations and harmful effects on our health (3).