On the pollutant hunt

As per the naaqm data for the year 1992, which covered 290 stations in the country, the annual values (minimum, maximum and annual average) for so₂ , no₂ (nitrogen dioxide) and spm -- also called critical pollutants -- are discussed herewith. For the first critical pollutant, so₂, the 41 reporting stations from the south (Kerala, Tamil Nadu, Pondicherry, Goa, Karnataka, Maharashtra and Andhra Pradesh (ap)), with the sole exception of Jagadamba centre in Visakhapatnam (ap), reported an annual average level at below 30 g/m 3 . Only Visakhapatnam needed a close watch as the peaks even crossed 200 g/m 3. Otherwise, the overall annual average for the southern states worked out at 13 g/m 3.

The states of Orissa, Madhya Pradesh (MP), Gujarat and the union territories of Daman and Diu and Nagar Haveli, had annual average so₂ concentrations on a slightly higher side compared to the south -- of the 36 reporting stations, three (one each at Nagda, Vapi and Ahmedabad) reported levels at 30 g/m 3 ; six stations reported peaks crossing 100 g/m 3 . The overall annual concentration was 16 g/m 3 .

In the north Indian states, of the 64 reporting stations, 13 posted annual average so₂ levels crossing 30 g/m 3 (one each in Punjab, Haryana and Delhi, two in Uttar Pradesh (up), and four each in Bihar and West Bengal-- wb). Gajroula, up, then the town with the highest so₂ concentration in India, reported annual averages of 114 and 131 g/m 3 from its two monitoring stations, with peaks crossing 300 g/m 3 . All stations in the Dhanbad-Jharia and the Calcutta-Howrah industrial belts had high so₂ averages, above 30 g/m 3 . The overall annual average levels of so₂ for the northern region was 23 g/m 3 .

Killer gas
In spite of minimum concentrations of no₂ emissions being more widespread than those of so₂ country-wide, the gas has not been accorded as much attention. In south India, annual average no₂ levels were reported at 22 g/m 3 , except at one location each in Kottayam (Kerala), Parel (Mumbai), Balanagar and Abids in Hyderabad (ap) and two stations at Visakhapatnam (ap). Peaks crossed 120 g/m 3 at all these stations. In central India, annual average no₂ levels crossed 30 g/m 3 at 11 stations (two each in Orissa and mp and seven in Gujarat) of a total of 36 reporting stations. Peaks crossed 120 g/m 3 at eight stations located in congested and high-traffic areas of large cities like Cuttack, Jabalpur, Surat, Baroda and Ahmedabad.

The situation is much worse in the northern region. Of the 64 reporting stations, 35 (seven in Rajasthan, all six in Punjab, five in Delhi, two in up, four in Bihar, eight in WB and three in Assam) reported average annual levels crossing 30 g/m 3 , with three stations even crossing 80 g/m 3 . Peak values were found to cross 120 g/m 3 at 22 stations, exceeding 200 g/m 3 at six. The overall annual average no₂ levels worked out to 29 g/m 3 .

Here, there and everywhere
spm concentrations over large tracts of India remain higher when compared to the West and, as such, the national ambient air quality standards allow higher annual average spm concentrations than permitted in Western countries.

Of the 41 stations monitored in south India, 21 satisfied the annual average criteria of 140 g/m 3 and all but one station (Jagadamba centre in Visakhapatnam) reported levels less than the 360 g/m 3 limit for industrial areas. But peak 24-hr concentration levels showed up at over 200 g/m 3 at all but six stations (two each in Chennai, Thiruvananthapuram and Kochi) and at over 500 g/m 3 at 10 stations. k r Circle in Mysore reported 677 g/m 3 at peak and 297 g/m 3 annual average levels. The highest peak was 1,238 g/m 3 at Chandrapur in Maharashtra. The overall annual average for the 41 south Indian stations was 155 g/m 3 .

Of 36 stations in central India, only four -- in Daman and Diu and Nagar Haveli -- met the 140 g/m 3 annual average limit and five stations in mp (two in Korba and one each in Satna, Jabalpur and Indore ) reported values far above the 360 g/m 3 annual average levels reported from industrial areas. Peak values crossed 500 g/m 3 at 22 stations.

In north India, of the 64 reporting stations, 13 (four in Assam, three each in wb and Punjab, one in Himachal Pradesh and two in Rajasthan) reported an annual average spm level of 140 g/m 3 ; 14 (two in Rajasthan, four in Delhi, and eight in up) had levels higher than 360 g/m 3 . The highest annual average of 866 g/m 3 was reported from Rajpur Road, Dehra Dun, up. The overall annual average spm level for all stations worked out to 273 g/m 3 .

More in the fray
Besides so₂, no₂ and spm levels, there are a number of other pollutants which are equally or more important from the point of view of public health. These include carbon monoxide (co), respirable particulate matter (RPM), lead, carcinogens like benzo(a)pyrene, ozone and several gaseous pollutants.

• Though it was one of the four air-pollutants for which national standards for ambient air quality were notified in 1982, CO is, even today, rarely being monitored, primarily because of the unavailability, cost and difficulties in maintenance and calibration of instruments for measuring co in low ranges (1-25 parts per million -- ppm). Limited monitorings at busy traffic junctions in large cities show that co levels are often much beyond permissible limits. At the ito crossing in Delhi, co levels are always over 10 ppm, peaking at 15.4 ppm.

• rpm has only recently been added to the list of pollutants requiring constant monitoring. Indications to date are that the prescribed limits of 60 g/m 3 are being crossed.

• Another toxin emitted mainly from petrol-driven vehicles is lead. At busy traffic crossings in Delhi, it has been recorded that the 1.0 g/m 3 limit prescribed for residential areas is being exceeded. The highest value recorded was 8.5 g/m 3 at Shahdara in 1992.

• The composition of spm determines the effects of various carcinogenic elements on public health. A large silica content in the respirable fraction of spm causes the deadly silicosis. Flyash from coal-fired thermal stations may contain a number of heavy metals like cadmium, chromium, nickel and arsenic.

• Data on benzo(a)pyrene and other carcinogens are not substantial. But the reported values of 150-750 g/m 3 in Mumbai and 30-750 g/m 3 in Delhi show that the levels of such pollutants are high and need to be monitored extensively and regularly.

• No monitoring has yet begun for ozone and other oxidants in India though these are now being regarded as the most critical air pollutants in the West.

• Gases like hydrogen sulphide, carbon sulphide, ammonia, carbon, hydrochloric acid, hydrogen fluoride and hydrocarbons need to be monitored around their respective sources of pollution; for example, ammonia emissions around ammonia or urea plants and carbon emissions around chlor-alkali plants.

G D Agrawal is the honorary advisor, Chitrakoot Gramoday Vishwavidyalaya, Madhya Pradesh.