Air pollution in ten Indian cities assumed alarming proportions and was linked to deaths of 33,000 people every year between 2008 and 2019, a study published on 6 July 2024 in the Lancet Planetary Health Journal points out. The report succinctly examined the link between short-term exposure to fine particulate matter (PM 2.5) and daily mortality rate. It also revealed an increase in the daily mortality rate even in cities where the levels of fine particulate matter were lower than the current Indian air quality standards. The cities included are Mumbai, Bengaluru, Kolkata and Chennai.

Meanwhile, Rohtak in Haryana state has been identified as the most polluted city in June this year, when compared to around 250 cities in the country as per a report early this month of the Centre for Research on Energy and Clean Air (CREA) based on data available from the Central Pollution Control Board (CPCB). The State of Global Air report 2024 clearly pinpointed the sad demise of 8.1 million people worldwide in 2021 which were linked to air pollution. It bears recall that the permissible annual average concentration of PM 2.5 exposure as per WHO guidelines should not exceed 5 micro gm/cubic metre for more than three to four days per year. The limit as prescribed by CPCB is 60 micro gm/cubic metre under the National Ambient Air Quality Standard (NAAQS).

The recent Lancet report clearly indicates the imperative necessity to revise existing pollution standards pragmatically. The recent database considered meaningfully, in addition to particulate matter PM 2.5 and PM 10, the mischief potential of ground measurements of nitrogen dioxide, which is a toxic gaseous material capable of penetrating deep inside the respiratory system. The highest concentrations of oxide of nitrogen were found in the Eastern Mediterranean region, a matter of grave concern. Thus, emissions reduction from industries, vehicles, biomass burning etc needs immediate attention.. The air quality of the National Capital Region has assumed alarming proportions in recent years. The action initiated by authorities to curb the menace is too little and too late, and it exposes the gross negligence of air quality management. The Indian Medical Association sounded an alert but the Delhi government locked horns with the Centre for its obligations and responsibilities and took the matter to the apex court.

Despite the National Green Tribunal’s stringent strictures in the past, no respite for the common people seems to be evident and the situation has deteriorated considerably. The smog, the fog and smoke contamination in northern parts of India extracts a heavy toll, and every day two lives are lost in India due to air pollution. The air we breathe is poisoned with anthropogenic and natural emissions all the time. 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 everexpanding technological society. The situation has been exacerbated by climatic change 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 ability”. Rainfall also helps in removing the impurities to a certain extent, but acid rain damages the environment, now a matter of grave concern. Therefore, any substance that is not a part of air’s gaseous make-up is regarded as a pollutant. Air-borne suspended particulate matter (SPM), respiratory particulate matter (RPM) and contaminant gases exist in the atmosphere in various degrees. Air pollution is not confined to a particular territory but is a trans-boundary phenomenon. In urban areas of India, the quality of air has been deteriorating rapidly over the past two decades. The problem is particularly acute in major Indian cities and its suburbs where the air is unclean according to standards fixed by the World Health Organization. Ever-increasing population levels also pose a serious problem. Emission from vehicles has been identified as a major source of pollution in the Delhi metropolitan region, and is said to be 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, multistoried building and road construction, ever increasing number of vehicles, whimsical burning of agricultural wastes, and emissions of SPM from thermal power stations are adding to the problem. The pollutants vary from one place to another. Their intensity is the most in the heart of the city. The common air pollutants in Delhi are sulphur dioxide, oxides of nitrogen, carbon monoxide, hydrocarbons, peroxyacetyl nitrite (PAN) which causes irritation of eyes, heavy metals and traces of incredibly dangerous polynuclear aromatic hydrocarbons (PAH) which are carcinogenic in character.

Air pollutants exist in gaseous or particulate form. Their concentrations are expressed most commonly either in micrograms per cubic meter (g to the power-3 of air) or as volume mixing rate (1 ppb =10 to the power-9 ) which are diverse in character. The poor and the weaker sections of society are acutely affected by pollution. The pavement dwellers, underprivileged and vulnerable groups are exposed to direct health hazards. Not surprisingly, the heavy air pollution leads to higher rates of mortality and morbidity. Leaded petrol has been banned in most developed countries. But unleaded petrol has disadvantages which need special attention. 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. Suitable measures need to be taken immediately to eliminate the emission of toxic benzene into the air. 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 absolutely necessary. The air quality monitoring process should be strengthened. The use of catalytic converters inside a car exhaust system has its benefits. The use of leadfree petrol in cars without converters is a great risk to public health. Personal exposure to benzene at service stations should be minimized. All service stations must display warnings about the risk of benzene exposure.

The vehicles that are running on outdated technology should be immediately discarded. Developing suitable sophisticated technology for manufacture of electric cars, gradually replacing diesel and petrol vehicles, would be beneficial. Planting more trees in the city can cleanse the air. Finally, the success of mitigating air pollution depends largely on the participation of people and their awareness of environmental health hazards.

(The writer, a former Reader in Chemistry at Presidency College, Kolkata, was associated with the UGC and UNICEF)