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even small increases in the levels of air pollutant ozone may have an adverse effect on the health of children, causing them to miss school, a new report suggests. "We detected ill health effects in school children because of levels well below the current air quality standard for allowable levels of ozone," said Frank Gilliland of the University of Southern California in Los Angeles, the us , who conducted the study.

Ozone is produced by a chemical reaction that occurs when sunlight hits air pollutants emitted in automobile exhaust. Breathing air with ozone can cause coughing, respiratory irritation, nausea and permanent damage to the lungs in people of all ages, but children and the elderly are especially vulnerable.

The investigators analysed daily levels of three common air pollutants -- ozone, nitrogen dioxide and fine particles -- and compared them with daily absenteeism rates of 2,081 student of fourth grade during the first six months of 1996. As the levels of ozone increased in the air by as little as 20 parts per billion, the researchers saw a simultaneous increase in the incidences of absenteeism due to respiratory illness by 83 per cent.