January 28, 2021 12:00:54 am
An international study led by researchers from the Indian Institute of Technology (IIT), Madras, has found chloride to be the highest inorganic fraction in particulate matter (PM), primarily responsible for haze and fog formation in northern India including the national capital. The study has been published in Nature Geoscience, a prestigious peer-reviewed international journal.
Previous studies in this regard have identified PM2.5 (particulate matter or aerosol particles with diameter less than 2.5 micrometre) as a major pollutant that is responsible for haze and fog formation over the Indo-Gangetic Plain, including Delhi. However, the role of PM2.5 and the detailed chemistry of haze and fog formation over the national capital has been poorly understood thus far. The study by IIT Madras greatly enhances our understanding about the precise role of PM2.5 in the chemistry of fog formation, which will help policy makers frame better policies for improving the air quality and visibility in northern India, said a statement issued by IIT Madras on Wednesday.
The study provides a scientific explanation for the source of high chloride in the PM2.5 mass over Delhi and quantifies its role in haze and fog formation and visibility reduction. It explains that complex chemical reactions involving hydrochloric acid (HCl), which is directly emitted from plastic-contained waste burning and other such industrial processes, is primarily responsible for high PM2.5 chloride and subsequent haze and fog formation over Delhi on chilly nights.
With the onset of the winters every year, most of the Indo Gangetic Plain is invariably engulfed in dense fog and haze, particularly during the months of December and January. Over the national capital, too, dense fog negatively impacts the air and surface transport, jeopardising human lives and resulting in huge financial losses.
Dr Sachin S. Gunthe, associate professor at the department of civil engineering, IIT Madras, who supervised the study, said that despite the absolute PM2.5 mass burden over Delhi being lesser than other polluted mega cities around the world – such as Beijing – the pollution and atmospheric chemistry of Delhi is much more complex to understand. The study put forward the importance of measurements to scientifically conclude that half of the water uptake and visibility reduction by aerosol particles around Delhi is caused by the HCl emissions, which are locally emitted due to plastic-contained waste burning and other industrial processes. Dr Gunthe said that the real challenge was to delineate the role of high chloride in visibility reduction.
The group of scientists and students involved in the study made use of state-of-the-art instruments to measure the chemical composition and other important properties of PM2.5, relative humidity levels and temperatures in Delhi. These instruments were operated round-the-clock for one month with extreme care and dedicated expertise and the observations were then used in complex chemical models.
The study was carried out in collaboration with Max Planck Institute for Chemistry, Germany; Harvard University, USA; Georgia Institute of Technology, USA; and Manchester University, UK. “This study is a demonstration of successful large scale scientific collaborations that are so vital for climate studies,” Dr Gunthe added.
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