Chloride-rich particles responsible for visibility reduction over Delhi: IIT-Madras study

Chennai: 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, primarily responsible for haze and fog formation in northern India, including Delhi.

The study has been published in the prestigious peer-reviewed international journal 'Nature Geoscience'.

Earlier studies had identified PM 2.5 (particulate matter or aerosol particles with a diameter less than 2.5 micrometre) as a major pollutant responsible for haze and fog formation over the Indo-Gangetic plain. However, the role of PM 2.5 and detailed chemistry of haze and fog formation over the national capital was poorly understood. This study will greatly enhance people's understanding about the precise role of PM 2.5 in fog formation and help policymakers frame better policies to improve air quality and visibility in the national capital, the researchers said.

Dense fog and haze engulf the Indo-Gangetic plain during the months of December and January. In Delhi, the dense fog impacts air and surface transport resulting in huge financial losses and jeopardize human lives.

The new study not only provides the scientific explanation for the source of high chloride in PM 2.5 mass over Delhi but also quantifies its role in haze and fog formation and visibility reduction. It explains that complex chemical reaction involving Hydrochloric Acid (HCl), which is directly emitted in the atmosphere from plastic contained waste burning and few industrial processes, is primarily responsible for high PM 2.5 chloride and subsequent haze and fog formation over Delhi during chilly winter nights.

The study led by IIT Madras was carried out in collaboration with Max Planck Institute for Chemistry, Germany; Harvard University, USA; Georgia Institute of Technology, USA; and Manchester University, UK.

Elaborating about the findings of this research, Dr. Sachin S. Gunthe, an associate professor in the department of civil engineering, IIT Madras, said, "We realized that despite absolute PM 2.5 mass burden over Delhi is much less than other polluted megacities 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 HCl emissions, which is locally emitted in Delhi potentially due to plastic contained waste burning and other industrial processes."

He hoped the research findings will help policy makers to efficiently enforce and implement policies that are already in place towards regulating open burning of plastic contained-waste and other potential chlorine sources.