Even at low levels, ozone can cause a number of respiratory effects. It is the brown-orange gas that lies over many urbanized areas. It is sometimes easier to see from tall buildings or other heights. Its primary component is ground level ozone, an invisible gas. Its visible portion is composed of particulate matter, or small bits of dust, soot, aerosols and other substances.
Ozone is a gas that occurs both in the Earth s upper atmosphere and at ground level.
In the Earth s lower atmosphere, near ground level, ozone is formed when pollutants emitted by cars, power plants, industrial boilers, refineries, chemical plants, and other sources react chemically in the presence of sunlight. Smog poses serious health hazards. It irritates the respiratory system, reduces lung capacity, can cause permanent lung damage following repeated exposures and can aggravate existing conditions such as asthma, bronchitis, emphysema and heart disease. Depending on the level of exposure, it also may cause symptoms such as coughing, choking, wheezing, nausea, chest pain, headache, difficulty breathing and eye irritation. People who already are especially vulnerable to air pollution are even more vulnerable to smog when exercising or engaging in serious work.