CHENNAI: A study led by researchers from the Indian Institute of Technology Madras (IIT-M) has found that burning of plastic and industrial processes to be primarily responsible for haze and fog formation in Northern India, including Delhi.
Sachin S Gunthe from the Department of Civil Engineering, who led the study, along with his teammates aimed to answer the question, “If overall PM2.5 mass burden over Delhi is much lower than polluted megacity of Beijing, then why is visibility reduction a major problem in Delhi?”
The ‘smog’ formation in Delhi and the rest of the Indo-Gangetic plain was attributed, by many studies, to PM2.5 (particulate matter or aerosol particles with diameter less than 2.5 micrometre). Further, the slash-and-burn agricultural practice has also been long seen as a reason for the haze. However, this study shows that chlorides in the PM2.5 mass over the region was the cause behind the poor visibility.
The role of PM2.5 and detailed chemistry of haze and fog formation over national capital was poorly understood, said a statement from the institution. This study aims to help policymakers frame better policies for improving the air quality and visibility in Delhi. The study has been published in the peer-reviewed International Journal Nature Geoscience.
The study explains the complex chemical reactions involving Hydrochloric Acid (HCl) that is directly emitted in the atmosphere from plastic-containing waste burning and a few industrial processes. The HCl from various sources combines with ammonia and condenses into an aerosol and exponentially increases its water uptake ability, eventually leading to dense fog formation. In the absence of the excess chloride, the fog formation otherwise would be suppressed significantly.
The study also suggests that the chloride pollution was also emitted locally. According to the statement, high PM2.5 chloride levels are primarily responsible for the 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.