Summer ’07: Hot days and unhealthy air

New data from the Central Pollution Control Board suggests that Delhi’s air now poses risks greater than ever before to your lungs, reports Avishek G Dastidar.

As if the intense heat this year was not enough, new data from the Central Pollution Control Board now suggests that Delhi’s air now poses risks greater than ever before to your lungs.

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An analysis of the air-pollution data by the Centre for Science and Environment (CSE) shows that the city’s daytime air this summer has been very high on ground-level ozone. This has resulted from a reaction between pollutants like nitrogen oxide (NOx) and hydrocarbons triggered by very strong sunlight.

Anumita Roychowdhury, associate director, CSE, said: "Ozone levels are expected to be higher in summer. But uncommonly high levels have been recorded this year."

The analysis shows that ground-level ozone, known as "bad ozone", was almost twice the permissible limit set by the WHO, which is 100-mg/cubic metre for an eight-hourly average. The ozone layer in the atmosphere, however, is good — it protects us from the sun’s ultraviolet rays.

In Siri Fort, the maximum level touched a dangerous 184.4 mg/cubic metre on June 10, while Bawana recorded 197.7 mg/cubic metre. The last time bad ozone crossed the WHO limit was in 2001, at 140-mg/per cubic metre.

Dr TK Joshi, head, Centre for Environment and Occupational Health, said: "People with cardiovascular ailments and asthma are at grave risk." The Environmental Protection Agency of the US said in a recent report titled Ozone-Good Up High Bad Nearby, that "ground-level ozone in the US is responsible for an estimated $500 million in reduced crop production... affecting the landscape of cities".