The air is heavy

The air is heavy

The euphoria over the growth in the diesel-powered private vehicular segment would evaporate if people were to open their eyes to the evidence on environmental and health hazards of diesel engines. Diesel engines are primarily responsible for harmful emissions of suspended particulate matter ( spm ) -- small particles which are respirable and extremely toxic -- along with oxides of nitrogen ( no x ) and ozone.

The Central Pollution Control Board ( cpcb ), New Delhi, has concluded that diesel is responsible for 100 per cent of the particulate matter produced by vehicles, 95 per cent of nitrogen dioxide ( no 2 ) -- considered the most dangerous of no x -- and 96 per cent of sulphur emissions. The cpcb does not measure ozone, an extremely harmful gas.

The World Health Organisation ( who ) has concluded that spm is the most serious air pollutant. Further, there is growing evidence that there is no safe level for particulate pollution. In other words, even if particulate levels are below the standards, they still remain dangerous to human health.

The Centre for Science and Environment ( cse ) conducted a detailed analysis of levels of diesel-related air pollutants in Delhi from data provided by the cpcb . The data is restricted to only three pollutants -- spm , no 2 and so 2 -- and is available for only the years 1987 to 1995. There is also data for 1996 for spm . The data shows the following:

SPM: In every breath you take
The annual average spm level in Delhi's air remained consistently high, much above national standards and total spm is constantly above the standard at all the monitoring stations almost every day of the year. The annual average maximum levels ranged from 7.6 times the permissible limit (140 microgramme per cubic metre) in 1988 to 16.7 times higher than the limit in 1992 (see graph: Total spm levels in Delhi ).

The cpcb does not monitor particles less than 10 microns (one micron is one-millionth of a millimetre) in size or pm 10 on a regular basis in Delhi. Called respirable suspended particulate matter ( rspm ), these particles cause the worst damage as they can penetrate deep into the lungs. The cpcb only monitors total spm . In other words, the quantity of all particles in the air. But short term monitoring of pm 10 levels by cpcb shows that, on an average, nearly 40 per cent of total spm in Delhi is pm10 . It is these particles which are most dangerous.

In 1998, cpcb monitored pm10 at the ito crossing. A cse analysis of the data shows that rspm levels were also well above the standard. In November, they went six times above the standard (see graph: rspm levels at ITO crossing ).

HEALTH EFFECTS:
A 1991-92 World Bank study on the health effects of air pollution in 36 Indian cities revealed that spm levels led to the premature death of 40,000 people every year in the cities surveyed. The study, repeated for the year 1995 by cse , showed that the number of deaths had increased to 52,000, a rise of 28 per cent in just three years.

The who has concluded that, on a worldwide basis, spm is the most serious air pollutant which is resulting in total excess deaths per year of 460,000 additional deaths. Scientists point out that not all particles are equally dangerous. It is pm 10 or less which are more dangerous. The worst, however, are fine particles which are less than 3.5-2.5 microns in size. Because of their size, these particles cannot be easily exhaled. They stay inside the lungs for a longer period corroding the cells, ultimately leading to the growth of a tumour.

According to a uk study conducted to understand which sources were contributing to airborne particulate matter in 1996, it was found that smaller the size of the particulate, the higher was their share in diesel emissions. While 17 per cent of pm10 and less was from diesel vehicles, as much as 52 per cent of pm 0.1 was from diesel vehicles (see graph: Size matters ).

The tinier the particulate matter the more harmful it is for human health. A recent uk study found that 90 per cent of the particles emitted by diesel vehicles are 1 micron or less. In other words, almost all particles produced by diesel are so fine that they penetrate deep into the lungs.

The California Air Resources Board ( carb ) formally designated diesel particulate as a Toxic Air Contaminant on August 27, 1998 which means that it has the potential to cause cancer. In addition, the Scientific Review Panel of carb has pointed out that chronic exposure to 1 microgramme per cubic metre (g/m 3 ) of diesel exhaust will lead to additional 300 cases of lung cancer per million people. Thus, for a population like Delhi, this means an additional 3,000 extra cases of lung cancer for a chronic exposure to 1 g/m 3 of diesel exhaust.

Further, particulate matter in diesel is coated with polycyclic aromatic hydrocarbons ( pah s), which are highly carcinogenic. Japanese scientists have discovered a new pah called 3-nitrobenzathrone in diesel exhaust, and they have found it to be the strongest carcinogen till date. Another mutagen known to exist in diesel exhaust is 1,8 dinotropyrene.

NO2 : Slow and steady rise
The levels of no 2 , a highly toxic gas which attacks the lungs, recorded in Delhi have been rising rapidly and so has the annual average. Though the annual average level remained below the standard, it has been increasing rapidly in the nine years from 1987 to 1995 (see graph: no 2 levels in Delhi ).

At the ito crossing, except for the monsoon months, there are several days when no 2 reaches critical levels. In the month of January and February 1998, no 2 levels exceeded the permissible limits by more than 1.5 times.

Haemoglobin is known to absorb no 2 more easily than oxygen. About 80 to 90 per cent no 2 inhaled is easily absorbed into the bloodstream. This reduces the oxygen-carrying capacity of the blood. no 2 causes lung tissues to become leathery and brittle and can cause lung cancer and emphysema (or severe breathing problems). Emphysema occurs due to the breakdown of the air sacs in the lungs, which then progressively diminishes the ability of the lungs to exchange oxygen and carbon dioxide in the blood stream. Thus, no 2 causes bronchitis and bronchopneumonia.

OZONE: The killer trend
Ozone is considered a secondary pollutant because it is produced as a result of the interaction of other air pollutants, particularly no x , which, in turn, the result of diesel vehicle emissions, and hydrocarbons, produced by both diesel and petrol cars. Because of a large number of two-stroke vehicles (two and three-wheelers), Delhi's air has high levels of hydrocarbons. In the presence of sunlight , no 2 reacts with hydrocarbons to produce ozone, a highly toxic gas, known to cause asthma. But the cpcb does not monitor ozone on a regular basis, except for one site, namely ito . A few studies done by the Central Road Research Institute ( crri ) and the School of Environmental Sciences of Jawaharlal Nehru University ( jnu ) show very high ozone concentrations in Delhi. In most cases, the maximum concentration of ozone has exceeded the upper limit of who guidelines by two times.

The 1989-90 study conducted by jnu reported high ozone levels during the summer months (June-August), especially around noon, and low levels during the winter months (November-January), which is in keeping with the trends noted worldwide. The maximum concentration was observed during August 1990.

Subsequent studies conducted by crri and jnu have revealed some unusual trends about ozone levels in Delhi. The crri study carried out in 1991 showed high ozone levels even during winter months, when "ground-based temperature inversion" is common. It appears that pollutants which lead to the formation of ozone get trapped in the inversion conditions which leads to high ozone levels even during the early hours of the day though traffic levels are low. As the day progresses, the pollutants get dispersed leading to reduced levels of ozone, which begin to build up again in the evening because of the inversion effect (see graph: Ozone levels in Delhi ).

A great deal of research has been conducted on the health effects of ozone which shows that it impairs the lung function and causes asthma. Ozone is absorbed by mucous membranes in the lungs by a process of dissolution in water. Since ozone is a powerful oxidant, it damages the nasal cavity and throat as well as sensitive parts of the lungs that are responsible for exchange of gases between air and blood circulation.

Children and young adults show greater risk to ozone exposure than older adults. And asthmatic children appear to be at special risk from ozone exposure.

Bad to worse?
The levels of pollutants in Delhi's air is already bad. And the unchecked growth of the dieselisation of the private automobile fleet and two-stroke vehicles means going from bad to worse. Already, diesel consumption has overtaken petrol in the last decade. Between 1980-81 and 1990-91, the growth rate of petrol consumption was higher than that of diesel but this trend was reversed during the period 1990-91 to 1996-97 when the use of diesel grew at a more rapid rate (see graph: Road rage ).