A study by researchers at the Indian Institute of Technology-Madras, in collaboration with experts from Germany, the U.K. and the U.S., has found that chloride-rich particles reduce visibility over northern India, including in New Delhi. The study was published in Nature Geoscience.
Several studies done earlier had identified that particulate matter or aerosol particles with a diameter less than 2.5 micrometres are a major pollutant, responsible for haze and fog formation over the Indo-Gangetic Plain.
Since the role of PM2.5 in haze and fog formation over Delhi and its detailed chemistry was not well understood, policies could not be developed to improve air quality and visibility, though it is a common knowledge that dense fog brings life to a halt, resulting in severe financial losses and endangering human lives.
The study explained that industrial processes and the burning of plastic waste were responsible for high particulate matter. They also caused complex chemical reactions involving hydrochloric acid (HC1), which is emitted in the atmosphere, resulting in haze and fog during chilly winter nights.
The study was carried out in collaboration with Max Planck Institute for Chemistry, Germany; Harvard University, U.S.; Georgia Institute of Technology, U.S.; and Manchester University, U.K. State-of-the-art instruments measured the chemical composition and other important properties of the particulate matter, besides the relative humidity and the temperature, in Delhi for a month. The findings surprised the researchers.
Sachin S. Gunthe, associate professor in the Department of Civil Engineering at the IIT-Madras, said, “We realised that despite absolute PM2.5 mass burden over Delhi being much less than the other polluted mega-cities around the world, including Beijing, the pollution and atmospheric chemistry of Delhi is much more complex to understand. This work put forward the importance of measurements and modelling approaches to scientifically conclude that half of the water uptake and visibility reduction by aerosol particles around Delhi is caused by the HC1 emissions, which is locally emitted in Delhi from the burning of plastic waste and other industrial processes.”
The real challenge was to delineate the role of high chloride in visibility reduction, he said. “The resolution of the mechanism was derived with the collaborative effort by all the partners with various tools of analysis. This study is a demonstration of a successful large-scale scientific collaborations that are so vital for climate studies,” he said.
Dr. Gunthe said, “Scientifically, our job is half-done. The burning of plastic waste can emit highly toxic chemicals called ‘dioxins’, which can accumulate in the food chain, causing severe problems in reproduction and the immune system. We further need to investigate in this direction. Enhancement in the fundamental science of air pollution should be given importance as much as technology development to tackle pollution.”
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