Cleaner air could bring down pollution deaths by 6.5 lakh in India: Study
If the low levels air pollution reached during the lockdown period are maintained, India’s annual death toll could reduce by 6.5 lakh, says a study by the Indian Institute of Technology (IIT) Delhi, and two Chinese universities – Fudan University in Shanghai and Shenzhen Polytechnic.
Restricted economic activity during the first month of the lockdown, which was the most stringent, saw a 52% average reduction in excessive risk (health risk assessment due to air pollution exposure) for particulate matter (PM) across India. The latest study also estimated a four-time decline in health risks associated with other pollutants.
Researchers studied concentrations of six pollutants, PM10 and PM2.5, carbon monoxide (CO), nitrogen dioxide (NO2), ozone (O3), and sulphur dioxide (SO2) between March 16 and April 14 from 2017 to 2020, in 22 cities across India. The study – ‘Effect of restricted emissions during Covid-19 on air quality in India’ – was published in the peer-reviewed science journal Elsevier Public Health Emergency Collection, earlier this month.
“If this low concentration during one month persisted for a year, it would save the lives of 6.5 lakh people, which would have otherwise been lost due to air pollution health effects,” said Sri Harsha Kota, corresponding author from IIT-Delhi.
A study by the Lancet Planetary Health journal, one of the first assessments for annual deaths due to air pollution, had recorded that close to 12.4 lakh deaths were attributed to air pollution in 2017 in India.
In the latest study, researchers calculated the average annual concentration for previous years (2017 to 2019), compared it with the reduced average concentration during the lockdown, and analysed it for the rest of the year. “At the same time, we calculated the health risk in both scenarios using base-line mortality and population data to arrive at this conclusion,” said Kota.
The pollutant measuring indicator – air quality index (AQI) – reduced by 30% pan-India, with a 44% drop in north India, 33% in the south, 32% towards the west, 29% for east, and 15% for central parts of the country, the study found.
Among major cities, Delhi observed the maximum AQI improvement of 49%. The study used air quality dispersion modeling (AERMOD) for the National Capital Region (NCR) where they considered meteorological factors during the lockdown and compared it with unfavourable weather conditions during November 2019.
“The results show that predicted PM2.5 could increase only by 33% during unfavourable weather. This means a significant improvement in air quality can be expected if strict execution of air pollution mitigation plans is implemented even if meteorological conditions are adverse,” said Kota.
Delhi NCR was followed by Kolkata at 44%, Mumbai at 38%, Bengaluru (32%), and Chennai (28%). “Using simulations such as chemical transport models, we saw that cities in north and east India, with very high air pollution, generally persisting during this time of the year, benefited most from the lockdown. However, with the advantage of sea breeze, Mumbai witnessed maximum reduction across peninsular India,” said Kota.
PM2.5 concentration reduction was a maximum across most regions, the study said. India witnessed a 43% drop for PM2.5, 31% for PM10, 10% for CO, and 18% NO2 during the lockdown compared to previous years. While there were negligible changes for SO2, a sharp rise (17%) was recorded for ozone concentration. Ozone, which affects climate, increased marginally (10-20%) across northern, western, and central India, but eastern parts saw a mammoth 89% increase compared to previous years.
“Whenever there is a decrease in PM, ozone increases as there is more sunlight [photochemical] penetration through the atmosphere,” said Kota, explaining that various Chinese studies had similar results during their lockdown period.
An independent expert, who was not part of the study, said the lockdown had helped identify new background air quality levels for different regions but cautioned about the surge in air pollution post lockdown. “The comparison with the World Health Organization (WHO) safe limits is not rational anymore, and we will realise after the lockdown that we can never reach the lowest levels of 10 micrograms per cubic metre, even if all anthropogenic sources are on hold. There is a need now for region-based air quality standards based on land-use pattern and socio-economic conditions,” said Dipankar Saha, former additional director, Central Pollution Control Board. “To boost the economy when the lockdown is called off, there will be a surge in emissions again but we must realise activities need to be opened up in a phased manner. Exceeding standards by 10-20% are acceptable but levels rising over 150% the safe limit will nullify all positive developments witnessed during the lockdown.”
‘NCAP needs to consider O3 as a secondary pollutant for city action plans’
India’s National Clean Air Programme (NCAP), which seeks to reduce pollution levels by 20-30% by 2024 across 122 non-attainment cities, identifies PM as the primary pollutant. However, the study suggested that secondary pollutants such as ozone also needed to be considered. “China’s Blue Skies Project went through a similar transition. India is already showing the indication of higher O3 levels when other pollutants reduce. During summer months, the Centre should consider precursors to ozone when they talk about non-attainment cities, and in addition to PM, O3 has to be kept in mind while preparing action plans,” said Kota.
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