Invisible India Gate due to Smog at Raj Path on November 08, 2020.

During winters, cities along the Indo-Gangetic Plains turn into hazy gas chambers year on year with little to no visibility. Interestingly, the visibility in these north Indian cities drops much lower even with similar and sometimes even lesser pollution compared to other parts of the world. The reason behind this has been a longstanding puzzle for scientists.

Now, a team of researchers from IIT Madras have attempted to solve this mystery. The lead author of this study, Dr Sachin S Gunthe, says that the research started with a fundamental question: If overall PM2.5 mass burden over Delhi is much lower than polluted megacity Beijing, then why is visibility reduction still a major problem in Delhi?

For the first time, they have tried to demystify the chemical compositions of winter haze to better understand this problem. And Chloride-rich particles were shown to be the reason behind the reduced visibility in cities like Delhi.

Chloride, the culprit

As the results indicated that the presence of chloride in particulate matter is the primary culprit that impacts visibility, the research took a bold new step towards solving the long-standing mystery behind extremely low visibility in northern cities. The findings indicated a persistent presence of high chloride in Delhi, while it was episodically high chloride in Chennai.

With the results from the first couple of days, it was very clear to us that Delhi is different; because generally for a polluted urban region like Delhi, one would expect sulfate to be the highest inorganic fraction of particulate matter; however, we found chloride to be the highest inorganic fraction of particulate matter, explains the co-author of the study Prof. R. Ravikrishna from IIT Madras.

Plastic burning to blame

The study states that a key ingredient for dampening visibility is the presence of Hydrochloric Acid (HCl), which is emitted through plastic burning and a few industrial processes. Moreover, the HCl concentration is also mixed with ammonia, which is also emitted in great amounts over the region. Together, they act as a deadly combo, causing around 50% of the reduced visibility, says the study.

Given that we find plastic burning as a potential cause of the reduced visibility, we hope these findings will help policymakers to efficiently enforce and implement policies that are already in place towards regulating open burning of plastic contained-waste and other potential chlorine sources, hopes Dr Gunthe.

The researchers claim that this is the first time that plastic burning has been linked to visibility and climate. Burning of plastic waste emits toxic fumes that are hazardous for human health. Now, the present study adds one more reason to tackle this menace posing risk to the lives of city residents. The poor visibility over the national capital region leads to financial burden and loss of human lives as it hampers the air and surface transport and results in deadly mishaps.

Chemical composition of pollution

None of the previous scientific studies has focused on the detailed chemistry of haze and fog formation over the Indo-Gangetic Plain, as per the official statement from IIT Madras. The current study sheds light on the precise role of PM2.5 in the chemistry of fog formation. Particulate matter or PM2.5particles of diameter less than 2.5 micrometreis regarded as a major pollutant in the National Capital Region.

The team deployed round the clock, state-of-the-art instruments to measure the chemical composition and important properties of PM2.5, along with relative humidity and temperature, in Delhi and Chennai. Furthermore, they used chemical models to process the observations and find answers.

Scientifically, our job is half done. Plastic-contained waste burning can emit highly toxic chemicals called dioxins, which can accumulate in the food chain causing severe problems with reproduction and the immune system. We further need to investigate in this direction. Enhancement in the fundamental science of air pollution should be given importance as much as technology development to tackle pollution, concludes Dr Gunthe.

The study has been conducted by the Indian Institute of Technology, Madras, along with researchers from Max Planck Institute for Chemistry, Germany, Harvard University, USA, Georgia Institute of Technology, USA and Manchester University, UK.

The study was published in the journal Nature GeoScience this week and can be accessed here.

Link:
Blinding Plastic: In a First, IIT Madras Decodes Chemistry Behind Low Visibility in Delhi | The Weather Channel - Articles from The Weather Channel |...