Delayed flights and trains, road accidents: What is causing thick fog in Delhi?

As a cold wave maintains its grip in northern India, a thick blanket of fog covers parts of the Delhi-National Capital Region (NCR). For more than a week, citizens of the National Capital have been waking up to hazy mornings as dense fog covered the city, leading to low visibility and traffic disruptions. Several trains and flights have also experienced delays in their operations because of the fog blankets. With temperatures dropping to almost seven degrees, the weather office has issued a warning of “dense to very dense fog” in Delhi and the neighbouring states of Uttar Pradesh, Rajasthan, Punjab, and Haryana. What causes fog in Delhi? How bad is the current situation? Why is a cold wave a common occurrence in the Capital? Let’s take a closer look. What causes thick fog in Delhi? Meteorologists attribute the current dense fog to the passing of a western disturbance, night moisture, clear skies and low wind speed. According to Indian Express which quoted India Meteorological Department (IMD) scientist Kuldeep Srivastava, moisture was brought in by a western disturbance that facilitated the creation of fog. In addition, the morning breeze was mild over the city.

“With faster winds, mixing takes place rapidly and fog will not form. There are a few factors that came together to contribute to the very dense fog cover on Monday. The presence of a significant amount of moisture and clear skies helped – when the sky is clear, the temperature tends to rise during the daytime, and in the early hours, the earth radiates this energy back to the atmosphere, contributing to the formation of fog,” he said. When temperatures drop at night and in the early morning, water vapour condenses and creates fog because colder air cannot store as much moisture as warmer air. In certain places, the amount of intense fog can also vary; for example, Palam may have denser fog than Safdarjung. RK Jenamani, also a scientist at IMD who spoke with the newspaper, explains this scenario: “Sometimes, there are local features that contribute to denser fog formation in some areas. Palam usually sees more fog hours than Safdarjung. In city areas, temperatures tend to be higher and moisture supply may be restricted because of concrete areas and roads.” Why is it a regular recurrence in the Capital? Along with low winds, low temperatures, and moisture availability, pollution particles present in the environment make the hazy conditions more noticeable, according to a 2022 report by Outlook India. Particulate matter, or aerosol particles with a diameter of less than 2.5 micrometres, or PM2.5, has been highlighted in numerous studies as a key pollutant that causes haze and fog development across the Indo-Gangetic plains, including Delhi. Additionally, haze and fog creation in northern India is mostly caused by burning plastic garbage, according to the report which cited a 2021 study conducted by the Indian Institute of Technology Madras (IIT-M). The study says the primary cause of high PM2.5 chloride levels and the haze and fog formation that ensue over Delhi on cold winter nights is complex chemical reactions involving hydrochloric acid (HCl), which is directly released into the atmosphere from burning plastic waste and certain industrial processes. It should be mentioned that the inversion height, or the point at which pollutants cannot be forced higher into the sky, decreases in the winter. Consequently, this causes pollutants to gather close to the ground. As a result, water vapour attracts more particles that condense close to the ground. [caption id=“attachment_13549202” align=“alignnone” width=“640”] Vehicles ply on NH-24 amid fog on a cold winter morning, in New Delhi. PTI[/caption] The processing of metal, e-waste, and plastics, as well as the burning of biomass and plastic-contained garbage, are among the small-scale enterprises that directly emit hydrochloric acid (HCl) into the atmosphere in Delhi. The excess ammonia in the environment is subsequently reacted with this HCl to create particulate ammonium chloride (NH4Cl). How bad is the current situation? The IMD has issued a warning of “dense to very dense fog in Delhi and Uttar Pradesh from 27 to 29 December and over isolated pockets of north Rajasthan and north Madhya Pradesh today. As per the Met Department, visibility recorded at 5.30 am today was Amritsar-0, Patiala, Srinagar, Bareilly, Lucknow and Prayagraj-25 metres, Varanasi-50, Jhansi-200, Ganganagar-50, Kota-500, Delhi-Safdarjung-50, Delhi (Palam)-125. Morning visuals from Delhi’s Dhaula Kuan, India gate, Barapullah, and the Delhi-Noida border area showed them engulfed in dense fog. The city’s air quality likewise saw a precipitous drop following weeks of good air. As measured by the Air Quality Index, the average air quality fell to 381, or “very poor.” Delhi’s minimum temperature fell to seven degrees Celsius, while the highest temperature of 24 degrees Celsius is predicted. The Capital’s Central Pollution Control Board’s (CPCB) air bulletin states that Anand Vihar had an AQI of 441 while Lodhi Road in central Delhi had an AQI of 327. The air quality at the IGI airport was 368. The AQI values for nearby Ghaziabad and Noida were 336 and 363, respectively. The forecast indicates that for the following week, the air quality will continue to decline. As per information sourced from the Delhi Airport FIDS (Flight Information Display System), the airport is facing delays affecting approximately 110 flights, both domestic and international arrivals and departures, due to dense fog. 28 international departure flights, 15 international arrival flights, 42 domestic departure flights and 25 domestic arrivals were affected as of 8.30 am on Wednesday. The Delhi Airport Authority has issued an advisory stating that while landing and takeoffs continue, flights not compliant with CAT III (category III) standards may face disruptions. Notably, CAT III refers to a type of instrument landing system that allows flights to land in low-visibility conditions such as fog, snow, and rain. More than 25 trains approaching Delhi or passing through Delhi stations are running late due to the dense fog. How is the number of accidents rising due to fog? Numerous collisions were reported on Uttar Pradesh’s roadways while they were still covered in fog. On the Agra-Lucknow Expressway, several cars crashed, leaving one person dead and twelve injured. A speeding truck in Bareilly collided with a house close to the Bareilly-Sultanpur route. The number of road deaths caused by foggy conditions grew to 14,583 last year, an increase of over nine per cent from 2021, according to data released by the Ministry of Road Transport. 15,597 people had major injuries. Uttar Pradesh had the highest number of these fatalities (3,920), followed by Madhya Pradesh (1,177), Tamil Nadu (1,032), and Bihar (1,842). With a maximum of 135 road deaths, Chennai was the city with the highest number of deaths, followed by Delhi with 132. Driving too fast and changing lanes when it’s cloudy and foggy are riskier, according to road safety experts. The Times of India reported that staying in the designated lane is crucial since fog makes visibility poor, making passing impossible.