New Delhi: Scientists have determined why smog forms at night during winters in the national capital, contrary to all the rules of atmospheric chemistry. For the past three years, New Delhi has been ranked the world’s most polluted capital. Its high levels of air pollution have been linked with a large number of premature deaths. In winter, the particulate matter levels exceed 500 micrograms per cubic meter of air. A team of researchers from the Paul Scherrer Institute (PSI) in Switzerland along with scientist from the Indian Institute of Technology (IIT) Kanpur and colleagues investigated the origin of these extremely high particulate levels in nighttime New Delhi in winter.
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“The chemical processes that take place in the air at night are unique to the Indian capital and have not been observed anywhere else in the world,” said Imad El-Haddad, an atmospheric chemist at PSI and one of the corresponding authors of the study.
The study, published in the journal Nature Geoscience, found that the trigger for the high levels of particulate matter is the fumes emitted when wood is burnt.
Wood burning is common practice for around 400 million people living in the Indo-Gangetic Plain, who use wood for cooking and heating.
In the absence of strict regulations, materials other than wood are also burnt, sometimes including plastic and other waste materials, the resaerchers said.
Such fires produce a mixture of gases containing countless chemical compounds, such as cresol, which our noses associate with the typical smell of fire, as well as sugar-like molecules from the burnt cellulose in the wood, they said.
These molecules, the team noted, cannot be seen in the air with the naked eye, even in high concentrations.
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However, as night falls the temperature in New Delhi drops so rapidly that some of the gas molecules condense and within a few hours clump together to form particles up to 200 nanometres across, which can be seen as a gray haze, they said.
Lubna Dada, an atmospheric scientist at PSI and one of the authors of the study said,
Condensation from gas to particulate phase resembles the way in which water droplets form on kitchen surfaces when one is cooking. Particles in the atmosphere act as large surfaces on which gases can condense.
This process, the researchers said, is very different from that in other places. Beijing, for example, is probably the best-studied megacity in the world in terms of its air pollution.
However, in the atmosphere of the Chinese capital, particle formation follow different chemical pathways, according to the researchers.
In China, the gases from emissions such as traffic and wood burning react in the atmosphere during the day when they are exposed to light resulting in the formation of less volatile fumes capable of forming particles during the haze, they said.
Such a pathway was also expected in New Delhi, however the opposite happens. Haze formation from the condensation of directly emitted fumes occurs at night, without photooxidation, driven by increased emissions together with a sharp decrease in temperatures.
Imad El Haddad added,
We have shown for the first time that semi-volatile gases can form such particles at night, contributing to the haze.
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(This story has not been edited by NDTV staff and is published from a syndicated feed.)
NDTV – Dettol have been working towards a clean and healthy India since 2014 via the Banega Swachh India initiative, which is helmed by Campaign Ambassador Amitabh Bachchan. The campaign aims to highlight the inter-dependency of humans and the environment, and of humans on one another with the focus on One Health, One Planet, One Future – Leaving No One Behind. It stresses on the need to take care of, and consider, everyone’s health in India – especially vulnerable communities – the LGBTQ population, indigenous people, India’s different tribes, ethnic and linguistic minorities, people with disabilities, migrants, geographically remote populations, gender and sexual minorities. In wake of the current COVID-19 pandemic, the need for WASH (Water, Sanitation and Hygiene) is reaffirmed as handwashing is one of the ways to prevent Coronavirus infection and other diseases. The campaign will continue to raise awareness on the same along with focussing on the importance of nutrition and healthcare for women and children, fight malnutrition, mental wellbeing, self care, science and health, adolescent health & gender awareness. Along with the health of people, the campaign has realised the need to also take care of the health of the eco-system. Our environment is fragile due to human activity, which is not only over-exploiting available resources, but also generating immense pollution as a result of using and extracting those resources. The imbalance has also led to immense biodiversity loss that has caused one of the biggest threats to human survival – climate change. It has now been described as a “code red for humanity.” The campaign will continue to cover issues like air pollution, waste management, plastic ban, manual scavenging and sanitation workers and menstrual hygiene. Banega Swasth India will also be taking forward the dream of Swasth Bharat, the campaign feels that only a Swachh or clean India where toilets are used and open defecation free (ODF) status achieved as part of the Swachh Bharat Abhiyan launched by Prime Minister Narendra Modi in 2014, can eradicate diseases like diahorrea and the country can become a Swasth or healthy India.