IIT Madras researchers find particles responsible for haze, fog formation in Northern India

Over the national capital dense fog negatively impacts the air and surface transport resulting in huge financial losses and jeopardizing human lives.

An international study conducted by the researchers from the Indian Institute of Technology (IIT) Madras has found out that chloride is the highest inorganic fraction in particulate matter, primarily responsible for haze and fog formation in Northern India including Delhi. The study has also been published in the journal Nature Geoscience. The study was led by IIT Madras and carried out in collaboration with Max Planck Institute for Chemistry, Harvard University, Georgia Institute of Technology, and Manchester University.

IIT Madras says many studies in the past have identified PM2.5 (particulate matter or aerosol particles with a diameter less than 2.5 micrometer) as a major pollutant, responsible for haze and fog formation over the Indo-Gangetic plain, including Delhi. The researchers say that the role of PM 2.5 and the detailed chemistry of haze and fog formation over national capital was poorly understood. Such a lack of understanding was the biggest hurdle in developing the policies to improve the air quality and visibility.
With the approaching winter season, every year, most of the Indo Gangetic Plain is engulfed in a dense fog and haze, particularly during the months of December and January. Over the national capital dense fog negatively impacts the air and surface transport resulting in huge financial losses and jeopardizing human lives.

The study explains that complex chemical reactions involving Hydrochloric Acid (HCl), directly emitted in the atmosphere from plastic contained waste burning and few industrial processes, is primarily responsible for high PM2.5 chloride and the subsequent haze and fog formation over Delhi during chilly winter nights.

The group of scientists and students deployed state-of-the-art instruments to measure the chemical composition and other important properties of PM2.5, along with relative humidity and temperature in Delhi, which were operated round the clock for one month. The observations were then used in complex chemical models.

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