Air quality has been a keen issue in India, especially over the Ingo Gangetic Plain during the post-monsoon and winter. As per recent studies, the deteriorating air quality in this part of the country is significantly posing health damage, leading to the loss of the county’s net human resources and economic prospects.

In the past few decades, the union as well as the state regulatory bodies have taken different action plans for mitigating the air quality problems. In recent times, the Govt. of India has launched a mega program called the National Clean Air Programme (NCAP) for the urban atmospheres of the country that do not meet the annual benchmark value of PM10 as prescribed by the Central Pollution Control Board (CPCB) of India.

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The cities that do not meet the PM10 benchmark values (60 µg m-3) are classified as non-attainment cities. The primary goal of NCAP was to reduce the annual PM10 concentration by 30 per cent in five years (2019-2024) in these non-attainment cities. Strategic action plans were suggested for different non-attainment cities after careful air quality monitoring and source identification studies.

Interestingly, Kolkata, the state capital of West Bengal, has also been enlisted as a non-attainment city under the NCAP programme. Although the city is enlisted among the non-attainment cities, the air quality of Kolkata significantly varies between seasons. While the summer and monsoon remain relatively clean and within the prescribed benchmark, the post-monsoon and winter seasons remain critically polluted, leading the annual average past the national standard.

The implementation of action plans as suggested by NCAP shows positive results in reducing the particulate matter, specifically PM2.5 concentration, over the city. A recent study published in a highly prestigious journal shows that NCAP has effectively reduced the PM2.5 concentration compared to the pre-NCAP era by reducing emissions from transport, industry, and secondary sources. However, the same study also mentioned that while NCAP is effectively reducing emissions from the above-mentioned sources, it is not as effective in curbing emissions from the biomass/trash/MSW burning and road dust for Kolkata. More interestingly, the study also suggested that even if the cumulative PM2.5 concentration goes low due to NCAP, the toxicity of PM2.5 in terms of its oxidative potential remains almost the same during the pre- and post-NCAP era.

PM2.5 can undergo a catalytic in situ reaction within the living human cell, generating reactive oxygenated species that create an oxidant/antioxidant imbalance in the cell, leading to damage or death of the cells. The capacity of PM2.5 to produce reactive oxygenated species in the living human cell is called its oxidative potential (OP). It should be mentioned that the OP of PM2.5 over Kolkata is manyfold higher compared with the advanced metro cities of Europe or the USA. Studies have shown that transition metals such as iron or manganese, along with toxic organic components released from road dust or open burning (MSW/trash or biomass), were the primary cause of the high OP value of PM2.5 over Kolkata. Hence, the policymakers associated with the air quality management of the city should be more focused on these two sources to reduce the toxicity of the aerosol and improve the quality of life of the citizens.

As we are near the great Indian festival Diwali, the emissions of transition metals and redox-active organic components from illegal firecrackers could increase the toxicity of aerosols to the highest level. A recent study of the atmosphere of the Sundarbans has shown how the acid dissolution of transition metals could increase the intrusive toxicity of the atmospheric aerosol, leading to significant damage to the environment and living organisms. The acid-dissoluted transition metals could also facilitate the formation of secondary particulate matter, causing high PM2.5 concentrations and associated effects over Kolkata. Hence, a strict ban should be imposed on the unauthorised firecrackers during the festival.

The writer is a national post doctoral fellow