On November 10, local time, the Diwali festival in India kicked off. Setting off fireworks during this festival, which is as important as the Chinese Spring Festival, is a local traditional custom and has also ushered in a new round of deterioration in the air quality in New Delhi, the capital of India.
Prior to this, residents in the capital had endured nearly a week of bad air that could be described as "toxic." For the record, New Delhi's air quality index (AQI) crossed 500 on November 6, with a number above 150 considered unhealthy. From November 3 to 9, the daily concentration of fine particulate matter with a diameter of less than 2.5 microns (PM2.5) in New Delhi reached more than 200 micrograms per square meter, 13 times the value recommended by the WHO.
Severe smog and air pollution forced schools to close, companies began to allow people to work from home, and the government recommended that children, the elderly and people with chronic diseases stay indoors as much as possible, but this did not stop people in the capital from celebrating the festival. After Diwali, New Delhi’s air quality index climbed to the 400-500 range. Some media reported that since November, the average air quality index in New Delhi has exceeded 350, with multiple communities exceeding the 500 mark, and the reading at a recording point in one community even reached an astonishing 999 - the pollution level exceeded the instrument examination range.
Such severe air pollution has attracted people's attention, but in fact, at this time of year, New Delhi, a megacity with a population of more than 30 million, will experience a baptism of air pollution. Scientists say that apart from the densely populated capital, other cities in India also suffer from air pollution during the windless season from October to December.
Most of India, including New Delhi, has a tropical monsoon climate, with strong monsoons in summer and windless seasons in winter. During the current season, less rainfall is available to wash pollutants out of the air. In addition, as temperatures drop, the height of the upper boundary of the troposphere decreases, which means that the space in the troposphere that accommodates human activities shrinks, leading to a greater concentration of pollutants within it.
Another culprit of air pollution is the farming practice of burning land. Farmers in northern India, especially wheat growers in the states of Punjab and Haryana northwest of New Delhi, still burn stubble to clear their fields in preparation for planting in the new year. A 2019 study found that 42% of the city’s black carbon emissions in fall and winter came from crop burning. Another study estimates that PM2.5 from crop burning can account for up to 50% to 75%.
However, the current situation in the Indian capital is somewhat unexpected. In an interview with Nature News, a policy researcher at the Energy, Environment and Water Resources Committee in New Delhi said that because the amount of crop burning in Punjab this year was lower than in previous years, people would have thought that the level of pollutants in the air would not rise too much, but in fact However, due to changes in meteorological conditions such as the decrease in monsoon wind speed, pollutants in the air have accumulated and the situation is getting worse.
In addition, the emissions from cities themselves are enough to create a toxic cocktail. Pollutants are produced by vehicle emissions, coal power plants, brick kilns, the burning of garbage, and the wood and charcoal used in homes to burn fires for cooking.
To make matters worse, pollutants already in the air may react with each other to form secondary pollution. When conditions are right, nitrogen oxides, sulfur oxides, volatile organic compounds and ammonia in the air will all react with each other to produce more fine particulate matter. PM2.5 and PM10 in smog have been shown to invade the lungs and sometimes even enter the bloodstream. Not only can they cause breathing difficulties and dry coughs, and eye irritation, long-term exposure has also been linked to cardiopulmonary disease, respiratory infections, and adverse birth outcomes. In South Asia alone, air pollution causes more than 2 million premature deaths each year, according to the World Bank.
This year’s Diwali is an important five-day festival in India from November 10th to 14th. To welcome Diwali, every household in India will light candles and oil lamps that symbolize light, prosperity and happiness. Many areas will also hold grand fireworks shows, which are as important as the Chinese Spring Festival. However, fireworks set off for Diwali increase the level of pollution. On the last day of Diwali, New Delhi became the most polluted city in the world, according to IQAir, a Swiss company that specializes in air quality monitoring. In an interview with the media, a doctor said that the air in the Indian capital now causes health damage equivalent to smoking 10 cigarettes a day.
Starting from November 13, New Delhi began to implement a week-long motor vehicle restriction. The rules are somewhat similar to those in Beijing: from 8 a.m. to 8 p.m., vehicles with odd-numbered numbers will travel on odd-numbered days, and vehicles with even-numbered numbers will travel on even-numbered days. However, some local scientists believe this approach has limited effectiveness. Because people will switch to motorcycles, which generally produce more pollution than cars. In addition, car drivers may choose to travel at night outside of restricted traffic hours. Due to low night temperatures, the troposphere itself is relatively small in size, which will only make pollution concentrations worse.
In fact, the smog-plagued Indian capital had two "smog towers" installed in 2021. It's an air purification system with giant fans capable of filtering 1,000 cubic meters of air per second, costing more than $2 million per "tower." However, studies have shown that this device can only purify the air within a few hundred meters of the surrounding area and is basically ineffective for most people in the city.
Another media report stated that the New Delhi city government is currently seeking permission from Indian federal agencies to artificially spray artificial rainfall agents such as silver iodide and dry ice above the city to induce precipitation. It is reported that the plan was developed by researchers from the Indian Institute of Technology (IIT) and is planned to be carried out in two phases. Experts suggest that the first phase could be implemented on November 20-21 and could cover a land area of 300 square kilometers. Rainfall washes away particulate matter from the troposphere, making the air cleaner and more transparent. In fact, New Delhi experienced brief rains during the first two days of Diwali, which did help bring down pollution levels.
However, some experts are not optimistic about the effectiveness of artificial rainfall. Polash Mukerjee, an independent researcher in the field of air quality and health, said in an interview with the media that although rainfall can immediately reduce air pollution levels, it can only last for 48 to 72 hours-pollution will rebound soon. In addition, the method of spreading artificial rainfall from aircraft is costly and diverts scarce resources to measures that have no clear or lasting impact and treats the symptoms rather than the root causes.
Another expert on climate change and sustainable development agreed, arguing that simply changing meteorological conditions such as rainfall or wind speed would not solve the pollution problem. Indian society needs to make a more concerted effort rather than piecemeal trial and error experiments.