Air quality in Delhi

11/22/24

Last summer, DC’s air quality index (AQI) climbed over 200, the sun became red, and heavy smoke filled the air. Stepping out of my apartment, the air felt nostalgic. I spent part of my childhood in Delhi. This past week, the AQI in Delhi reached 490, categorizing the air quality as "severe plus."

Schools closed down, offices went remote, nonessential construction and demolition projects were banned, trains were canceled, and flights were diverted or delayed. Some people brought out their N95 masks, some people roamed around without; some could work from home and some, like street vendors, rickshaw drivers, or the homeless, didn’t have a choice. Angry reddit threads piled up.

Sources: Central Pollution Control Board, Govt. of India; EPA Air Quality Tracker; IQ Air; EP&CCD Punjab.

To make sense of the graph, AQI ranges from 0 to 500 (different countries have different standards). It was developed by the EPA and is calculated by converting measured pollutant concentrations to a uniform index.

Delhi suffers mainly from fine particulates, PM2.5, a tiny toxic particle that settles deep into lungs and organs, wreaking havoc on immune defenses. Air pollution in Delhi shortens the lives of its residents by 11.9 years, according to the Air Quality Life Index (AQLI) at UChicago. A 2021 Study found that adolescent children living in Delhi had a higher BMI and a higher prevalence of asthma, respiratory symptoms, allergic rhinitis, and eczema than their South Indian counterparts.

I kept seeing cigarette smoke equivalents to air pollution in the news, so I took PM2.5 concentration data and converted it to a number of cigarettes passively inhaled using Berkeley Earth’s rule of thumb: 22.2 μg/m3 of PM2.5 is 1 cigarette.

Source: Central Pollution Control Board, Govt. of India

Source: Google Search Trends

What happens in November? Diwali, for one. And post-harvest agricultural waste burning.

Uttar Pradesh, Punjab, and Haryana, key agricultural states close to Delhi, have two growing seasons: May to September (Kharif) and November to April (Rabi). Many farmers plant rice in May and wheat in November. They burn their fields in late September to get rid of the rice debris. This practice, called stubble burning, is illegal, but it’s also the quickest and cheapest way to get fields ready to harvest wheat. In 2008, the government mandated that Northern farmers sow rice later to take advantage of the rain. This means they're burning their fields later too.

Burn a field in September, and the wind causes the smoke to wither away. But burn one a month later, and the smoke travels to nearby cities like Delhi. Harvard researcher Tina Liu found that the delay in timing also increased the number of fires, which is also increasing greenhouse gases.

The same situation is playing out 263 miles away in Pakistan’s Lahore. As the city’s AQI reached 500, the city went into “green lockdown:” schools, offices, bazaars, and public spaces have been closed. Hundreds have been hospitalized. UNICEF’s representative in Pakistan said the smog was so bad that it was visible from space. One of the causes repeatedly blamed in both Delhi and Lahore is stubble burning. Pakistani Punjab's senior minister Marriyum Aurangzeb asked Indian Punjab to collaborate on a joint plan to tackle smog, as some smog from India came into Lahore.

But farmers make up a small part of the problem and take much of the blame. Currently, the Indian Institute of Tropical Metereology estimates stubble burning to contribute an average of 20% to Delhi's PM2.5 concentration. But according to a 2023 review, stubble burning makes up about 3-4% of the annual average PM2.5 concentration, making the problem much bigger than just agriculture. Year-round, most pollution comes from vehicle exhaust (10-30%), followed by road and construction dust (10-30%), power plants (10-30%), cooking and heating (10-30%), open waste burning (5-15%), dust storms (<5%), and Diwali firecrackers (<1%). Similarly in Pakistan, the AQLI suggests that 45% of the air pollution comes from vehicle emissions and 40% comes from industrial emissions.

Source: What Is Polluting Delhi’s Air? A Review from 1990 to 2022. Sustainability. 2023; 15(5):4209. https://doi.org/10.3390/su15054209

The winter is also a strong trap for pollution. Delhi in the winter doesn’t have the volume of wind needed to disperse emissions like the monsoon. At the same time, the city sees a rise in emissions from burning coal, biomass, and waste for warmth.

What’s the government doing about it?

The Delhi government is looking into inducing artificial rain, but until they get approval from the federal government, 114 water tankers have been deployed to sprinkle water around the city.

Delhi’s considering the odd-even experiment again, where vehicles with registration numbers ending in odd numbers could drive on odd days and even numbers on even days. When it was implemented in January 2016, there was some improvement, but April 2016 and November 2019’s attempts saw no noticeable difference in pollution.

But the quick fixes to this yearly problem - lockdowns, sprinklers, artifical rain - won't nudge the deeper roots. Delhi's public transportion is poorly connected and expensive. The bus system is unreliable, underfunded, and overloaded. There isn't much incentive to get out of private vehicles, which are the worst emitters of PM2.5. Long-term solutions include increasing infrastructure for public transportation, walking, and cycling; promoting the use of clean fuels, enforcing emissions standards for industries, improving waste management, and increasing the city’s green cover. I was excited when Delhi's first tree census was launched last year. But almost a year later, the data hasn't been released.

What's left is to come up with a solution.