Pollutants found indoors are similar to those found outdoors and, in some instances, they actually come from outdoor sources, according to a new study, `Exposure Assessment in the Middle Class Sub-population of East Delhi', which is being conducted by Dr Mahendra Pandey, a scientist at the Central Pollution Control Board (CPCB), and Dr Nandita Shukla, a research assistant with the Council of Scientific and Industrial Research (CSIR).

The study reveals that Mayur Vihar in east Delhi presents a classic example of a residential area where the indoor concentration of Suspended Particulate Matter (SPM) was found to be almost double of that found outside.

Heavy traffic on the nearby highways, proximity to the NOIDA industrial belt and flyash from the nearby power plants contribute to the poor ambient air inside houses in Mayur Vihar and the surrounding areas of east Delhi.

The levels of SPM - a dangerous pollutant emanating from diesel vehicles - at all locations in east Delhi was found to be lower during the day than during the night owing to the phenomenon of `atmospheric inversion', which is active at sunset and prevents dispersion of air pollutants during the night.

After sunrise, the earth's surface gets heated and the convective currents generated rise vertically till noon and gradually erode and destroy the ground inversion layer formed and stabilised during the evening.Car exhaust and fine particles can readily infiltrate into houses especially if windows are kept open, but there are significant internal sources of pollution adding to the problem.

A variety of pollutants originate inside houses from such human activities as cooking, cleaning, smoking and heating. Many studies have shown that the concentration of pollutants inside the kitchen can be sixty times higher than that found in the outside environment.

If raw fuels such as cow dung, wood, leaves and sawdust are used, the problem naturally becomes worse because organic fuels generate thousands of pollutants, including carcinogens, increasing the risk of lung cancer. Women are naturally at a greater risk. But the east Delhi study shows that even in houses where relatively safer fuels such as cooking gas are used, the concentration of pollutants could be significantly higher than in the outside air nearby.

In fact, almost none of the middle-class families surveyed used raw biomass fuels such as cow dung or firewood and separate investigations had to be mounted to discover the source of pollutants.

According to Dr Pandey, while pollutants disperse rapidly outdoors, they stay trapped indoors for a very long time, increasing the exposure level of the residents. Chronic effects of indoor pollution include inflammation of the respiratory tract and reducing resistance to respiratory infections, which in turn enhances susceptibility to the inflammatory effects of smoke and fumes to establish a vicious cycle of pathological changes.

Most pregnant women in India are already anemic due to malnutrition and at such a stage, exposure to pollutants, particularly carbon monoxide (CO), is naturally dangerous, Dr Pandey said. The biological effects of CO exposure on the foetus and newborns are not yet clear but studies have shown that babies delivered by mothers who live in high indoor concentrations of CO weigh less than those delivered by mothers living in normal conditions. High concentrations of CO may be found in kitchens and living rooms in which cooking gas is used improperly and without proper ventilation and some cases of fatal poisoning have been reported in the winters.

In east Delhi, 23 per cent of the population was found to be suffering from severe respiratory disorders while another 31 per cent was found to be suffering from mild or moderate breathing problems. Adult females were the worst sufferers from ailments such as asthma and allergic rhinitis, further confirming that people who stay indoors are exposed more to pollutants.

The main problem with indoor pollutants is that most of these are smaller and can be inhaled easily. Called respirable particulate matter (RSPM) these pollutants easily penetrate into houses.

According to Dr Nandita Shukla, a research assistant with the Council of Scientific and Industrial Research (CSIR), each house resembles a reaction vessel in a laboratory with chemicals continuously entering and exiting.

Some of these chemicals can react with one another creating products such as free radicals which are potentially irritating and would be negligible were it not for continued renewal.

Other products of indoor chemistry are more stable than free radicals but are difficult to detect using the sampling and analysis techniques currently applied to indoor air.

Dr Pandey and Dr Shukla say that effective techniques exist to control indoor pollutants but these call for much higher levels of public awareness and cooperation. Meanwhile, the only people who benefit are chemists selling drugs for respiratory disorders at an increasing rate of twenty per cent per annum in Delhi.