According to the ministry officials, these trees have a high air pollution tolerance index (APTI) and can catch and contain dust or smog, absorb pollutants and improve the ambient quality. The ministry has recommended that saplings of these trees be grown in the city's nurseries in large numbers and also be used for systematic plantation.

Says Conservator of Forests M.S. Negi: ``We had compiled a report some time ago wherein we had identified and listed trees that absorb different types of pollution. For instance, if Neem is good for absorbing noise pollution, bamboo and peepal are good for absorbing dust, heat and other emissions.''

``The ministry has recommended that these trees be planted especially around the industrial areas. This will create a curtain of sorts, which would absorb the pollutants and save the adjoining residential areas from their harmful effects.''

The list of trees is divided into four parts based on their APTI for an effective check on pollution. Part-I (which includes trees like Mango, Sehjana Phali, Kathal, Molshree, Banyan and Pilkhan) lists evergreen trees that have a dense canopy and can screen all kinds of pollutants if planted in large numbers.

Part-II has trees that may be raised to absorb pollutants and improve the air's ambient quality. These are comprised of Mango, Sheesham and Jamun trees.

Next come those species of trees that can absorb the left-over pollutants. The list, which is made up of 11 species, includes Neem, Dhaak, Cassia, Ashok, Acacia, Kadamb, Mahua and Peepal.

The fourth list is made up of trees that have a low APTI but are indicators of the level of pollution. It is suggested that these trees -- Kaint, Papri, Kachnaar, Silver Oak, Amla, Jacaranda, Gular -- be planted in all the curtains and used to monitor the air pollution level of the area.

Admitting that there was very little space available in and around industrial areas, Negi said: ``We can plant them on roadsides, in vacant spaces along the roads, gram sabha land and wherever else we get space.''

Negi added that many of these species were already being grown in their nurseries and were being planted in the city as well as distributed free of cost to residents as well as organisations. Plants which absorb dust, temperature and emissions from traffic and industries: Neem, Bamboo (Baans), Amaltaas, Sheesham, Peepal, Molshree, Mango, Jamun, Arjun, Teak (Sangwaan), Imli (Tamarind).

Plants that can be used to restore and landscape garbage dumps: Babool, Subabool, Arjun, Gulmohar, Jacaranda, Siras, Amaltaas, Eucalyptus, Kadamb.

Plants that check noise pollution: Ashok, Cassia, Neem, Kachnaar, Banyan, Peepal, Jacaranda, Jangal-Jalebi, Semal.

Plants suitable for areas where gaseous pollutants are dominant: Acacia, Bel-Pathar, Ulu-Neem, Siras, Neem, Bougainvillea, Sheesham, Peepal, Mahua, Hibiscus and Imli (Tamarind).