colourless gas formed from chemical reactions between nitrogen oxides and hydrocarbons in the presence of sunlight near the earth's surface.

Ozone (O3) that occurs near the surface of the Earth. In pollution it causes concern because of its toxic effects.

Secondary ozone pollution, formed through photochemical processes in the atmosphere at the presence of nitrogen oxides, volatile organic compounds and sunlight.

ozone (03) that occurs near the surface of the Earth. It is a pollutant of concern in smog because of its toxic effects.

ozone that is formed in the troposphere when chemicals produced by cars, power plants, factories, and other pollutants are baked in the hot sun. Ground-level ozone makes it hard for us to breathe, and is harmful to the leaves of plants and trees. (Back to Ozone Action! Days)

Formed by a reaction between nitrogen oxides and volatile organic compounds in the presence of sunlight. Levels have been greatly increased by human activities such as the burning of fossil fuels.

Ozone is produced at ground level when some of the chemical components of vehicle exhaust and industrial emissions react with sunlight. At ground level, ozone is a powerful and irritating pollutant. In fact, it is the main component of smog. (See also Ozone, Stratospheric ozone).