The quality of Kolkata’s air has assumed alarming proportions. The city’s pollution level in the middle of this month has been higher than that of Delhi’s, according to the US Consulate in Kolkata, which had made an estimate of the pollutants. However, West Bengal’s environment minister and the Mayor of Kolkata have categorically refuted the assessment, iterating that conditions will improve by the end of winter.

Be that as it may, the air pollution data report of the US Consulate can differ from the findings of the West Bengal Pollution Control Board, and the variation is not unlikely for various reasons. The technique adopted covers the quality of high-volume air sampler equipment, chromatograph attenuator adjustment, chemicals used, sensors and auto analysis of ambient air quality procedures. But this does not imply that the Consulate’s report is absolutely wrong.

The PCB’s data states that the particulate matter is much higher than that of Delhi. For example, its report of 15 January, as available on the website, indicates the presence of pollutants in ambient air in south Kolkata. These are: sulphur dioxide 12.0; PM 2.5 – 169.0; nitrogen dioxide – 63.17; PM10 – 311.33 (all values are in microgram/cubic meter) and the Air Quality Index (AQI) is 338 which is extremely poor, as per guidelines framed by the World Health Organisation.

The Green Bench of Calcutta High Court has directed that no fuel will be given to any vehicle in the city unless the pollution control certificate (PUC) is furnished. It has also raised a pertinent question ~ Why is compressed natural gas(CNG) not used in Kolkata as in other cities? It criticised the authorities for the indifference towards air pollution which has assumed “gruesome proportions”, according to WHO and UNEP (United Nations Environment Program).

Delhi has recently adopted stringent measures following a stricture from the Supreme Court. These steps include the use of compressed natural gas (CNG) and plantations. Kolkata on the contrary has effected virtually nothing. The air we breathe is poisoned with anthropogenic and natural emissions. However, air pollution is not a new problem. As long as man has lived in cities, he has developed a propensity to pollute the air. It is a problem of the ever-expanding technological society.

Most artificial impurities are injected into the atmosphere at or near the earth’s surface. Therefore, what is critical about air pollution is its scope and severity. It is well known that for most pollutants the troposphere cleanses itself within a very short period of time because of the so-called “vertical mixing tendency”. Rain also helps remove the impurities to a certain extent, but acid rain damages the environment. Therefore, any substance that is not part of the air’s gaseous make-up is regarded as a pollutant.

Air-borne suspended particulate matter (SPM), respiratory particulate matter (RPM) and contaminant gases like volatile organic matter exist in the atmosphere in various degrees. The size of particulate matter (PM) is an extremely important factor in order to understand its impact on the human body and the absorption potential in the throat and lungs. If the PM is larger than 10 micrometers in diameter, it gets trapped in the nose and throat and never affects the lungs.

On the other hand, particles smaller than 2.5 micrometers in diameter percolate to the bronchial tubes and can enter the deepest portions of the lungs. In Kolkata, air pollutants exist in gaseous or particulate form. Their concentrations are expressed most commonly either in microgram per cubic meter (gram to the power-3 of air) or as volume mixing ratio (1 ppb=10 to the power-9) which are diverse in character. Toxicological, clinical and epidemiological studies revealed the danger of PM inhalation leading to chronic lung diseases, inflammation, irritation of lungs, susceptibility to viral and bacterial pathogens, changes of blood chemistry, causing carcinoma and heart attacks.

Air pollution is not confined to a particular territory but is a trans-boundary phenomenon. In the major urban cities, the quality of air has been deteriorating rapidly over the past two decades. The problem is particularly acute in Kolkata and its suburbs where the air is unclean, according to standards fixed by the World Health Organisation. The city’s ever-increasing population, expected to be around 15 million by 2020, is posing a serious problem. Emission from vehicles has been identified as the major source of pollution in the Kolkata metropolitan region. It is responsible for nearly 60 per cent of the city’s total pollution level. The situation is appalling owing to the increasing number of vehicles and the limited space for their movement.

Domestic consumption of fossil fuels, sometimes out in the open and pollutants from small industries and godowns are further accentuating the problem. The pollutants vary from one place to another. Its intensity is maximum in the heart of the city. The common air pollutants in Kolkata are: sulphur dioxide, oxides of nitrogen, carbon monoxide, hydrocarbons, heavy metals like lead, and traces of dangerous carcinogenic polynuclear aromatic hydrocarbons (PAH). In order to minimise the effect of air pollution and make the city a better place to live, work and invest in, the British Overseas Development Administration has advanced certain recommendations, called the Calcutta Environment Management Strategy and Action Plan (CEMSAP).

It has identified auto-emissions from the vehicles of outmoded technologies as solely responsible for environmental hazards. The CEMSAP has also pointed out that the 24-hour average concentration of SPM, sulphur dioxide, nitrogen oxides, carbon monoxide and hydrocarbons in some parts of the city are far above the limits of the Central and State Pollution Control Boards. The air pollution index (API) is the highest at the Howrah Bridge approach, followed by the BBD Bag area.

The roadside air quality is far worse than the standards for all pollutants. The menace is horrendous in the headquarters of Nadia, Hooghly, Burdwan districts. The poor are the worst affected. The pavement dwellers, underprivileged and vulnerable groups are exposed to direct health hazards. The dense air pollution leads to higher rates of mortality and morbidity.
Lead petrol has been banned in most developed countries.

But unleaded petrol has other disadvantages which need to be addressed. Lead-free petrol releases a higher level of aromatic organic compounds and a high concentration of benzene which is known to be potentially carcinogenic. According to WHO, the risk of cancer is substantial.

Given the horrifying level of air pollution in Kolkata, how is it that millions manage to survive? One probable explanation is that the ambient air pollutants are shared by millions of people and they act as biological filters. The body doesn’t immediately suffer any symptoms of danger, but they do arise after a prolonged period of time. As the pollutants are chiefly the outcome of auto-emissions, the entire auto-emission regulatory process needs to be revamped immediately.

Reduction of vehicular emissions through continuous check, strict enforcement of the law and periodical survey of the emission control equipment are imperative. The air quality monitoring process should be strengthened.

The vehicles that are run on outdated technology should be immediately discarded. Special emphasis should be given to the use of natural gas (CNG). The use of catalytic converters inside a car exhaust system also has its benefits. The use of lead-free petrol in cars without converters is a danger to public health. Personal exposure to benzene at service stations should be minimised. Planting more trees can cleanse the air.

The quality of fuel used in automobiles also helps curb air pollution. Its samples need be analysed regularly. The infrastructure must be suitably developed and the equipment for continuous auto-emission control, including, mobile laboratories, need to be utilized properly. The success of mitigating air pollution depends largely on popular participation and awareness of the environmental health hazards emanating from the problem of auto-emission.

The writer, a former Reader in Chemistry, Presidency College, Kolkata, was associated with UGC and UNICEF.