Study links chloride to fog and haze in Delhi

A study published in a prestigious peer-reviewed International Journal Nature Geoscience has found Chloride to be the highest inorganic fraction in particulate matter, primarily responsible for haze and fog formation in Northern India including National capital Delhi.

Chennai: An International Study led by Researchers from Indian Institute of Technology Madras has found chloride to be the highest inorganic fraction in particulate matter, primarily responsible for haze and fog formation in Northern India including National capital Delhi.

The study has been published in a prestigious peer-reviewed International Journal Nature Geoscience.

Many studies in the past have identified PM2.5 (particulate matter or aerosol particles with diameter less than 2.5 micrometres) as a major pollutant, responsible for haze and fog formation over Indo-Gangetic plain including Delhi. However, the role of PM2.5 and 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.

This study not only provides the scientific explanation for the source of high chloride in PM2.5 mass over Delhi but also quantifies its role in haze and fog formation and visibility reduction. The study explains that complex chemical reactions 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 PM2.5 chloride and the subsequent haze and fog formation over Delhi during chilly winter nights. While previous researchers also have observed high chloride in PM2.5, the potential source of such a high chloride and if it played any role in haze and fog formation was a scientific mystery.

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

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 with extreme care and dedicated expertise. The observations were then used in complex chemical models.

The study identifies waste burning as a major pollutant source, which is responsible for emissions of aerosol precursors as well as other toxic substances such as chlorinated dioxins and other persistent pollutants that affect human health. The study also emphasised need to improve the policies related to air pollution, solid waste management including e-waste, and food safety to systematically address the environmental issues in India.