India’s capital, New Delhi, is preparing a new weapon in the fight against deadly air pollution: cloud seeding. The experiment, which could take place as early as next week, would introduce chemicals like silver iodide into a cloudy sky to create rain and, it’s hoped, wash away the fine particulate matter hovering over one of the world’s largest cities.
The need is desperate. Delhi has already tried traffic restriction measures, multimillion-dollar air filtration towers, and the use of fleets of water-spraying trucks to dissolve the particulate matter in the air—but to no avail.
The use of cloud seeding, if it goes ahead, would be controversial. “It’s not at all a good use of resources because it’s not a solution, it’s like a temporary relief,” says Avikal Somvanshi, a researcher at the Center for Science and Environment in New Delhi. Environmentalists and scientists worry that most of the government’s response is focused on mitigating the pollution rather than trying to cut off its source. “There is just no political intent to solve this, that is one of the biggest problems,” says Bhavreen Kandhari, an activist and cofounder of Warrior Moms, a network of mothers demanding clean air.
The air is so bad that schools in Delhi and its surrounding areas have announced closures, and offices are allowing employees to work from home. The government has advised children, elderly people, and those with chronic diseases to stay indoors as much as possible. Diesel trucks, except those carrying essential goods, are no longer allowed into the city. Spells of rain last week cleaned up the air, but the respite was short-lived as air quality worsened again, aided by firecrackers set off over the weekend to celebrate Diwali, the Hindu festival of lights.
Now, Delhi officials are seeking permission from federal agencies in India to try cloud seeding. The technique involves flying an aircraft to spray clouds with salts like silver or potassium iodide or solid carbon dioxide, also known as dry ice, to induce precipitation. The chemical molecules attach to moisture already in the clouds to form bigger droplets that then fall as rain. China has used artificial rain to tackle air pollution in the past—but for cloud seeding to work properly, you need significant cloud cover with reasonable moisture content, which Delhi generally lacks during the winter. If weather conditions are favorable, scientists leading the project at the Indian Institute of Technology in Kanpur plan to carry out cloud seeding around November 20.
Until then, at least, Delhi will remain shrouded in a thick gray haze, which has become a toxic winter ritual. The smog, a dangerous cocktail of particulate matter and noxious gasses, results from a series of unfortunate events that happen at the start of winter.
In late October, farmers in northern India, particularly wheat growers in the states of Punjab and Haryana northwest of Delhi, use a cheap and easy method to clear their paddy fields for fresh sowing—lighting fires to burn off stalks left behind after harvesting. In doing so, they inadvertently send plumes of smoke into the air. Authorities have tried to convince farmers to switch to using machines to remove crop residue instead of burning it, but farmers can’t always afford that method. Some small startups turn the crop residue into pulp that can then be used to make cardboard items. State and federal governments have also been looking into paying farmers to not burn their fields.
Even on the worst days, smoke from crop burning only accounts for about a third of Delhi’s pollution, says Somvanshi. And just stopping farm fires won’t make the smog go away because there’s no dearth of polluting activities in and around Delhi—coal-fired power plants, brick kilns, burning garbage, household usage of wood and charcoal for cooking, and more.
As if external sources aren’t enough, fine particulate matter can also form through chemical reactions. When conditions are right—a little moisture in the air, low temperatures—all the gaseous pollutants, specifically nitrogen oxides, sulfur oxides, volatile organic compounds, and ammonia, start reacting and create secondary particulate matter, says Somvanshi. Almost 25 percent of fine particulate matter (an air pollutant abbreviated as PM 2.5) in Delhi is caused by this reaction. Secondary particulate matter formation is also a risk with cloud seeding, says Gufran Beig, a meteorologist and air pollution expert at the Indian Institute of Tropical Meteorology. For air quality to improve significantly, you need heavy and sustained rainfall. If cloud seeding is able to produce only drizzle, then humidity will rise, likely spurring secondary aerosol formation, he says.
Part of the blame for Delhi’s winter smog also lies with an atmospheric phenomenon called inversion. In summer, air near the ground is warmer, while air at greater heights is colder. As a result, whatever is emitted on the ground naturally rises up with the hot air and is dispersed, says Somvanshi. When winter sets in, things get inverted, quite literally. “As the ground temperature falls, the air right next to the ground becomes cooler, and as you go up it gets hotter,” he says. A layer of cold, heavy air forms across northern India, stopping any vertical movement. Being a landlocked city, Delhi doesn’t have sea breezes to move the pollution horizontally, says Somvanshi. As a result, the pollutants have nowhere to go.
The resulting haze puts a natural sepia filter on the city at dusk. Across Delhi, digital screens display in neon letters the Air Quality Index (AQI), a measure of the concentration of pollutants in the air. The World Health Organization recommends that the average AQI over a 24-hour period be less than 15. Delhi’s city-wide average AQI most days this month has been over 350, data from the Central Pollution Control Board shows. One neighborhood maxed out the recordable level of 999 and several crossed the 500-mark.
The most harmful ingredients in this deadly mix are PM2.5 and PM10—airborne particles or aerosols only a few microns in diameter—which enter your body when you breathe and lodge themselves in the lungs, even entering the bloodstream sometimes. In the short term, they can cause difficulty breathing and leave you with long, dull headaches, itchy eyes, or a persistent dry cough. Prolonged exposure to fine particulate matter has been linked to heart and lung diseases, respiratory infections, adverse birth outcomes, and more. According to the World Bank, air pollution is responsible for more than 2 million premature deaths annually in South Asia alone.
Throughout the pollution season, Delhi restricts construction activity to reduce the amount of dust in the air and uses water trucks to try to dampen remaining dust. The city also has two “smog towers”—air purifier systems with giant fans that filter 1,000 cubic meters of air per second and cost more than $2 million apiece. But studies show that they only clean the air a few hundred meters around them and are largely ineffective.
One measure that does target emissions directly is the odd-even policy, where vehicles with odd license plate numbers are allowed on the streets on odd dates and those with even numbers on even days. But Delhi imposes the rule sparingly, and it only applies to a small segment of vehicles, says Beig. “It doesn’t really mean anything if you are taking out one bucket of water from the ocean,” he says. To really work, rules like odd-even should be applied throughout the year, says Kandhari. For that, Delhi needs a better public transport system, she adds.
The silver lining is that annual average PM 2.5 levels in Delhi have been declining, albeit gradually, since 2015, Somvanshi’s research has shown. This improvement is visible during the summer and monsoon months, when weather conditions are friendlier, he says.
Kandhari says her biggest fear is of not seeing a smog-free Delhi in her lifetime. Surprisingly, despite the seasonal outcry, Delhi’s bad air hasn’t become an electoral issue. And so, ahead of general elections next year, Kandhari has one important request for her fellow Indians: When politicians come to you for your vote, ask them where clean air is on their list of priorities.
