Return of the smog

the deadly smog that engulfed the capital in winter last year is back, and much earlier too. "Due to a drop in temperature during winter, the Earth's surface cools faster than the atmosphere. In such conditions, the layer of air between the Earth's surface and the atmosphere -- up to 900 metres from the ground -- undergoes inversion. This means that instead of rising up into the atmosphere, the layer remains over the surface. As a result, the dust and emissions from vehicles remain suspended in this layer of air," says S C Gupta, director, regional office, Indian Meteorological Department. When mixed with sufficient moisture in the air, it gives rise to a haze, which is dispelled only when the Earth's surface warms up towards noon, he says.

Giving reasons for the early appearance of smog this year, Gupta says that rains and heavy winds usually sweep pollutants away, thereby not allowing smog to gather. This year, the usual rains from the western disturbances have not taken place leading to the persistence of a dry spell in October. "We are also experiencing light winds and low temperatures in the days which enable the lower particles to remain in the air, thus giving rise to smog," he adds.

Seasonal variation show a dangerous build-up of air pollution during winter. For instance, in December 1998, the levels of tiny particles less than 10 microns in size -- particles that are highly toxic and penetrate our lungs -- had become eight times the prescribed standards.

This year too, doctors in Delhi have reported an escalation in the number of smog-related respiratory diseases. As the intensity of smog increases, the incidence of heart and bronchial diseases also rises. R K Goel, director, department of environment, believes that cases of asthma in Delhi are 12 per cent above the national average. A study conducted by J N Pande, Narendra Bhatta and G C Khilnani, Ambient Air Pollution and Casualty visits at aiims, says "there is a marked increase in asthma and chronic obstructive lung disease cases in November and December, when the smog levels are maximum."

Says S K Chhabra, department of cardio-respiratory physiology, Vallabhai Patel Chest Institute, who is at present conducting research on air pollution-related illnesses, "The smog is harmful because of its particulate content. It is harmful for people who have pre-existing lung diseases such as asthma and bronchitis."

The situation gets critical during the festival of Diwali. The Central Pollution Control Board had set up a monitoring station at the Bahadurshah Zafar Marg in 1997. On the day of Diwali, the suspended particulate matter (spm) levels doubled as compared to the previous day. Another study conducted at the All India Institute of Medical Sciences, (aiims), New Delhi, in 1997-98 revealed that the number of asthma cases increased dramatically after Diwali. "For a week after Diwali, cases keep pouring in," says J N Pande, professor and head, department of medicine, aiims.

Smog is also taking a toll on new-born infants. Every day about 30 cases of respiratory problems come to Kalawati Saran Children's Hospital. Many complain of bronchiolitis, a viral infection, that has attained alarming proportions due to high levels of ambient air pollution. Doctors at the hospital say that not only are the number of patients increasing but the intensity of the spasms is also becoming more frequent every year. Scientists believe that air pollution can stunt the growth of foetuses and may finally result in abnormalities in the child.

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