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Sulphur dioxide
Suspended particulate matter
Carbon monoxide
Oxides of nitrogen


Figure 1 indicates the location of the current GEMS/Air monitoring sites operated by NEERI. These three sites monitor SO2, suspended particulate matter (SPM) and nitrogen dioxide (NO2). Monitoring was discontinued at these sites in 1988 and recommenced in January 1990. All three stations have been moved in the past and therefore only long-term data from 1980 onwards are presented here. It should also be noted that the NEERI site classifications used in this report are different from those given by the GEMS/Air data base. The data presented in this report are taken directly from NEERI sources.

In 1978 BMC set up nine monitoring stations in Bombay measuring SO2, SPM and NO2. In 1984 there were 20 stations in operation. Very few details have been provided as to the location of these sites, the monitoring methods used or any results other than annual mean concentrations (for an unknown number of sites). This would suggest that the BMC's results should be made widely available for assessment. lf valid, these data would prove invaluable due to their geographic spread.

Spot carbon monoxide (CO) and hydrocarbon (HC) monitoring have been undertaken at a number of roadside sites in the past. However, at present there is no co-ordinated monitoring programme for CO, ozone (O3) or HC.

Sulphur dioxide

Emissions :
Figure 2 shows that industrial sources account for nearly all SO2 emissions in Bombay. Following a 66 per cent increase in SO, emissions between 1970 and 1980 the rate of increase has slowed significantly over the past ten years. In 1990 estimated total SO2 emissions were around 157,000 tonnes per annum. This levelling off in emissions is largely due to the introduction of natural gas as a major fuel source, from the newly opened gas fields located off the west coast. An inventory of SO2 emissions from industrial sources conducted in 1973 is presented in Table 1. Although the industrial structure of Bombay has changed considerably since then, it can be assumed that the current distribution of emissions is similar. The chemical industry was found to be the principal source of SO2 (NEERI, 1991a).

Ambient Concentrations:
Ambient SO2 monitoring at the three GEMS/NEERI sites reveals that annual mean concentrations having dropped significantly between 1980 and 1987 to below WHO annual guide levels, had increased substantially in 1990 (Figure 3).However, annual mean SO, concentrations are still within the WHO guideline range (NEERI, 1980, 1983, 1988, 1990, 1991a, 1991b). Annual data from Bombay Municipal Corporation for 1978-1988/89 show a similar trend (NEERI, 1991a).

Monitoring conducted in the Air Pollution Survey of Greater Bombay 1970-73 indicates that SO2 levels first started to decrease in the 1970s, probably due to planning measures such as the relocation of industry and increased stack heights. Annual mean SO, concentrations of 67 micro g m-3, 63 micro g m-3 and 53 micro g m-3were recorded in 1971, 1972 and 1973 respectively (NEERI, 1991a).

Seasonal Variation in SO2 concentrations is minimal; peak concentrations occur in January - the coldest month of the year (NEERI, 1988).

Suspended particulate matter

Suspended particulate matter emissions have increased significantly in recent years and are projected to continue rising into the next century (Figure 2). As with SO2, industry is the dominant source, accounting for 93 per cent of all emissions. Table 1 indicates that in 1973, 67 per cent of all industrial SPM emissions were caused by power plants (NEERI, 1991a).

Domestic emissions have remained relatively constant in the past and are forecast to remain stable despite the projected increase in population. This is in part through the switch from biofuels, such as wood, charcoal and animal dung and also coal, to less 'dirty' fuel such as liquid petroleum gas (LPG) and kerosene (NEERI, 1991a).

Suspended particulate matter emissions attributable to Transport, have increased greatly. The Transport sector doubled its share in total estimated SPM emissions between 1970 (2 per cent) and 1990 (4 per cent). However, these estimates are extremety low considering Bombay's motor vehicle population. Recent estimates suggest that transportation, especially motor vehicles, accounts for approximately 35 per cent of particulate emissions in the Greater Bombay area. (Shah, 1992). This proportion is likely to increase further with in-creasing motor vehicle traffic. Diesel vehicles and very old vehicles are the main source of particulate in the Transport sector. Cars and trucks are the major source of Transport SPM (NEERI, 1991a). The low proportion of estimated domestic emissions may, in part, be due to difficulties in adequately quantifying domestic sources. Other inventories suggest that over 20 per cent of total SPM emissions originate from domestic sources (Shah, 1992).

Ambient Concentrations:
Ambient air quality monitoring at the three GEMS/NEERI sites reveals that both annual mean (Figure 4) and 98th percentile (Figure 5) TSP levels are higher at the residential monitoring station at Bandra than at the commercial and industrial sites, where one would expect motor vehicle and industrial emissions to dominate (NEERI, 1980, 1983, 1988, 1990, 1991a, 1991b). This may indicate an underestimation of the contribution of domestic sources in the emissions inventory. Alternatively, as suspended particulate matter concentrations at the residential site have increased in line with those at other sites, it is possible that this site may be heavily influenced by Transport emissions as it is close to the busy Swami Vivekanand road. Transport SPM emissions may also have been underestimated in the NEERI inventory.

Smoke from diesel vehicles is of great concern as its constituents (e.g., polycyclic aromatic hydrocarbons) are carcinogenic. The popularity of two-stroke engines in autorickshaws and motorcycles is also a factor for consideration. Two-stroke fuel requires the addition of engine oil which, when burnt in the combustion process, produces the characteristic blue smoke.

Ambient SPM concentrations are likely to increase further in the coming decade unless control measures are adopted. The increase in industrial productivity is the greatest contributor to increasing SPM emissions.

However, it should be noted that SPM concentrations in the early 1970s were higher than those during the 198Os; an annual mean of 380 micro g m-3 was calculated for 1973 (NEERI, 1991a).

Mean monthly SPM concentrations are considerably reduced during the monsoon (June to October). Monsoon levels are approximately half those of the winter (November to February).

Analysis of SPM in the Air Pollution Survey of Greater Bombay 1971-73 indicated a high proportion of organic matter; 10 sites throughout Bombay gave a mean of 46 per cent. It is this organic matter which is the greatest risk to health, thus suggesting that the natural dust component in Bombay, which is non-volatile, is not as great as in other Indian cities such as Delhi.


Ambient Concentrations:
Table 2 shows monthly mean lead (Pb) levels in SPM sampled at 10 sites in Bombay during the Air Pollution Survey of Greater Bombay 1971-73. Monthly mean values were found to exceed the WHO annual guideline (1 micro g m-3) at seven of the 10 sites; the mean across all 10 sites was 1.4 micro g m-3 with a maximum of 2.4 micro g m-3 at the Goregaon site. This wide distribution would suggest that petrol-driven motor vehicles are the main source of ambient Pb. The number of petrol-driven motor vehicles has risen from approximately 125,000 in 1971, to 468,000 in 1987 and to 588,000 in 1989. The Pb content of petrol in India in 1986 was 0.800 g /l for premium and 0.560 g /1 for regular (Octet). The current mean Pb content of petrol from the Bombay refineries is 0.155 g/l (Indian Department of the Environment cited by NEERI, 1991a). Monitoring undertaken at the GEMS/NEERI sites in 1990 indicates that annual airborne Pb levels have fallen significantly since the 1970s to between 0.25 and 0.33 micro g m-3 well below the WHO guideline of 1 micro g m-3 (NEERI, 1991c). It is likely that kerbside levels will be much higher. Lead in street dust is also likely to be high and accumulation and resuspension will also result in increased personal exposure.

Carbon monoxide

The increase in motor vehicle population is reflected in CO emissions from this source. Estimated emissions have increased from 69,000 tonnes per annum in 1970 to 188,000 tonnes per annum in 1990-91 (Figure 2). This increase is likely to continue into the next century; NEERI estimate that CO emissions will be almost 255,500 tonnes per annum by 2000. Most of this increase is attributed to motor vehicle Transport which is estimated to be responsible for 89 per cent of total CO emissions in 1990 (NEERI, 1991a).

It is estimated that domestic CO emissions account for 11 per cent of the total in 1990. Over the past 20 years the proportion of domestic CO has decreased as the Transport sector has gained in importance. However, domestic emissions have increased overall and are likely to increase further in coming years. Changes in fuel use are likely to reduce domestic emissions (LPG produces CO). Increasing population will result in greater energy demand and hence increased emissions of CO. Recent research on CO emissions suggests that domestic sources and in particular biofuels, such as wood, charcoal and dung, make a larger contribution to anthropogenic and urban emissions than originally believed. Personal exposure, especially indoors (kitchen) is a very important factor for consideration when examining health effects. Forecasts based on increasing industrial activity indicate that 1 per cent of CO emissions will be from industrial sources by 2000 (NEERI, 1991a).

Ambient Concentrations:
Monitoring of CO is not undertaken by NEERI in Bombay at the present time. However, the Maharashtra State Pollution Control Board have undertaken a number of short-term roadside surveys between 1984 and 1987. Carbon monoxide levels were monitored at several roadside sites during periods of peak traffic flow (i.e., 0800-1200 hours and 1700-2100 hours). Eight-hourly mean concentrations ranged between 4-20.6 micro g m-3, a maximum hourly concentration of 50 micro g m-3 was recorded at the Haji Bachoo Ali Hospital. Maximum hourly concentrations are generally around 23-29 micro g m-3 - below the WHO guideline value (micro g m-3). It is important to realise that these are results from roadside surveys and are not representative of ambient background CO levels which, due to Bombay's favourable meteorology, are likely to be quite low.

Oxides of nitrogen

Estimated and projected emissions of oxides of nitrogen (NOx) (as NO2) are presented in Figure 2. It would appear that although emissions are increasing, largely as a result of the contribution of increasing Transport emissions, the rate of increase has slowed significantly in the 1980s and that since 1980 industrial emissions have to a large extent stabilised. NEERI projections indicate that despite increasing productivity industrial emissions will remain around 27,000 tonnes per annum by 2000. It is difficult to see how this stability has been achieved and how it will be maintained given the increase in industrial productivity. The switch to natural gas is likely to increase NOx emissions significantly. In 1973 power plants were the main source of industrial NO, followed by chemical works (Table 1) (NEERI, 1991a).

Transport is estimated to account for 52 per cent of NO, emissions in 1990 and it is projected that Transport emissions will have increased by approximately 14,600 tonnes per annum by 2000.

Detailed vehicle emissions inventories produced by the Indian Department of the Environment (NEERI, 1991a) indicate that diesel vehicles (predominantly trucks) are the dominant source of motor vehicle derived NO, in Bombay.

Ambient Concentrations:
Nitrogen dioxide is monitored at all three GEMS/NEERI sites in Bombay. Figure 6 shows the trend in 98 percentile NO2 concentrations between 1982 and 1990 at the GEMS/NEERI stations. Levels of NO2 increased Until 1985. In 1990 98 percentile values were similar to those in 1982 (70-85 micro g m-3). Concentrations at all three GEMS/NEERI sites remain relatively consistent suggesting that NO2 concentrations are evenly distributed throughout the city (NEERI, 1980, 1983, 1988, 1990,1991a, 1991b). This would point towards secondary NO2 formation. Annual mean trends produced by BMC in Bombay and Chembur have been significantly lower than those observed at GEMS/NEERI sites since 1983. However, as no details of monitoring methodology and site location have been provided for the BMC sites, direct comparison of the data is not attempted (NEERI, 1991a).

Diminished insolation during the monsoon period reduces photochemical conversion of nitric oxide (NO) to NO2 and therefore ambient levels are lower during this period. Maximum concentrations occur in winter, particularly in November and December.


Ambient Concentrations Ozone is not routinely measured in Bombay. Increasing NO, and hydrocarbon emissions and relatively high insolation imply that if O3 is not already a problem in the Bombay region it is likely to become a problem during the 1990s. Continuous monitoring of urban O3, however limited, should be regarded as a major priority by the authorities in order to identify if and when ambient urban O3 becomes a threat to human health.


Air Pollution Situation:
Bombay has some specific air quality problems mainly attributed to increasing industrialisation and motorization.

On a positive front, planning enforcement measures, such as the relocation of industries and increased stack heights, together with the introduction of natural gas have proved to be partially successful in slowing the decline in air quality and should be encouraged further. Low-sulphur coal, a relatively small motor vehicle population and the scrubbing effect of the monsoons helps to reduce overall ambient concentrations in the city.

Main Problems:
Heavy industry on the island tends to create most of the pollution which is often blown by westerly winds over New Bombay on the mainland. Direct comparison Of SO2 levels in 1976 revealed that concentrations in New Bombay were twice those on the island.

The most important threat to air quality comes from the projected rise in urban population, which is forecast to increase by approximately 5 million between 1990 and 2000. This scale of increase will result in a huge increase in domestic emissions alone, simply for cooking and heating purposes. As population increase outstrips infrastructure development, such as electric supply from gas-powered power stations, people will be forced to use, or revert to, 'dirty' ,fuels. The speed of development necessary simply to house and provide employment for this growing population means that proper planning measures cannot be adopted. Air quality considerations are very often a low priority.

Urban sprawl off the island will inevitably result in an increased number and length of motorised trips, this leading to congestion and increased emissions.

Control Measures:
The most effective methods of preventing worsening air quality in Bombay relate to slowing the rate of urbanisation, in order to allow proper development of infrastructure and urban planning. Any further relocation or decentralisation of industry in the Greater Bombay region should recognise possible impacts upon surrounding and/or neighbouring areas. This also applies to the location of residential areas adjacent to large industrial sites.

Health effects Between 1977 and 1983 the Environmental Pollution Research Centre, Department of Respiratory Medicine, at KEM Hospital conducted a comparative epidemiological study of 4,129 residents from the Khar (low), Chembur (moderate) and Lal Bag (high) districts of Bombay and a rural (control) area situated 40 km from the city. Standardised prevalence for number of disorders were determined and classified according to SO2 levels (Kamat and Doshi, 1987).

Table 3 shows that people living in areas with elevated SO2 (i.e., > 50 micro g m-3) suffered an increased prevalence of dyspnoea (breathing difficulties), coughs and common cold. The 'urban low' area had the lowest morbidity except for cardiovascular disease. The moderately polluted area showed a higher level of morbidity for common colds, intermittent cough and dyspnoea. Rural prevalence were not as low as might have been expected. However, the villages studied had no sanitation, to protected water supply, poor housing, widespread use of hazardous cooking fuel, poor nutrition and poorer medical care than in Bombay. All these factors will inevitably influence the health and lung function of the rural community. It should be noted that the rural sample showed better lung function at older ages. In all areas young children (under five) and the elderly showed the greatest respiratory morbidity.

The study also revealed a significant correlation between NO2 and frequent colds; NO, and SPM and coughs; and between SO2, NO2, SPM and dyspnoea and chronic cough. The frequency of common colds was observed to decline due to changes in industrial fuel use (switch to natural gas) and a strike.

Cross-sectional studies showed higher morbidity among slum residents, particularly in the urban medium pollution load area, probably due to confounding factors similar to those which influence morbidity in the rural population. Nutrition, occupation and smoking were shown to affect morbidity in addition to air pollution. Relatively constant weather conditions throughout the year mean that seasonal influences were found to be of little significance in terms of health effects.

Examination of standardised mortality data from between 1971 and 1979 also revealed that higher respiratory cardiac and cancer mortality were associated with high air pollution.

A vehicle pollution component was added to the study in 1982. Carboxyhaernoglobin (COHb) levels in blood were related to traffic flow and clinical symptoms. Higher levels of COHb were found in areas with slow-moving traffic with heavy or moderate vehicle densities. People living inflates facing road traffic also showed higher COHb levels. The only significant correlation between elevated COHb and symptom morbidity was an increase in the incidence of chest pain and irritability.


Faiz, A., Sinha, K., Walsh, M. and Varma, A. 1990 Automotive Air Pollution: issues and options for developing countries, World Bank Policy and Research Working Paper WPS 492, The World Bank, Washington DC.

Kamat, S. R. and Doshi, V. B. 1987 Sequential health effects study in relation to air pollution in Bombay India, European Journal of Epidemiology 3,265-277.

NEERI 1980 Air quality in selected cities in India 1978-1979, National Environmental Engineering Research Institute, Nagpur.

NEERI 1983 Air quality in selected cities in India 1980-1981, National Environmental Engineering Research Institute, Nagpur.

NEERI 1988 Air quality status in ten cities in India 1982-1985, National Environmental Engineering Research Institute, Nagpur, India.

NEERI 1990 Air quality status in ten cities in India 1986-1987, National Environmental Engineering Research Institute, Nagpur. (Unpublished report).

NEERI 1991a Air pollution aspects of three Indian megacities, Volume II: Bombay, National Environmental Engineering Research Institute, Nagpur.

NEERI 1991b Air quality status 1990, National Environmental Engineering Research Institute, Nagpur.

NEERI 1991c Air quality status: Toxic metals, polycyclic hydrocarbons, anionic composition and rain water characteristics (Delhi, Bombay and Calcutta), National Environmental Engineering Research Institute, Nagpur.

Shah, J. 1992 Personal communication, The World Bank, Washington DC.

UN 1989 Prospects of World Urbanisation, 1988, Population Studies, No. 112, United Nations, New York,

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