Delhi woke up to its pollution crisis in October 2016, when the city experienced smog episodes with PM2.5 levels—dangerous fine particulate matter—reaching 750 micrograms per cubic metre, 12 times the safe limit. 

In response, the Aam Aadmi Party government implemented the "Odd-Even" scheme to reduce vehicular emissions. However, the scheme's impact has yet to be measured. In addition, the same year, the Supreme Court directed the Ministry of Environment, Forest and Climate Change (MOEFCC) to devise a coordinated plan to tackle pollution episodes, resulting in the Graded Response Action Plan (GRAP) in 2017.

However, the capital’s pollution crisis has been decades in the making. 

India introduced landmark legislations, such as the 1981 Air (Prevention and Control of Pollution) Act and the 1986 Environment (Protection) Act, to curb pollution. However, Delhi's air pollution crisis dates back to the 1990s. During this decade, rapid urban growth and industrialisation overwhelmed any impact of these legislative measures.

In 1996, the Centre for Science and Environment released its Slow Murder report, chronicling the city's worsening pollution. This report spurred the Supreme Court to intervene, demanding an action plan from the Delhi government.

Delhi’s government proposed its first air pollution control plan in 1998 and launched the Environment Pollution (Prevention and Control) Authority (EPCA) in 1998. The Authority introduced compressed natural gas (CNG) for public transport vehicles, reducing emissions from buses and auto-rickshaws.

However, in the 2000s, Delhi's population grew exponentially—from 16.6 million in 2001 to over 46 million by 2011. The number of registered vehicles, too, grew from 4.24 million in 2004 to over 10.8 million in 2018. The city’s public transportation infrastructure buckled under the pressure of overpopulation. 

At the same time, Delhi saw an industrial relocation as many factories moved to NCR towns outside the capital city’s borders. This only created new pollution hotspots. Other factors include burning crop residue in neighbouring states, particularly during winter, when weather conditions trap pollutants closer to the ground.

Transparency and monitoring showed some progress during the 2010s. In 2009, the National Ambient Air Quality Standards were revised to include 12 pollutants. In 2014, the National Air Quality Index(NAQI) was introduced. The NAQI simplified air quality data into accessible categories, raising public awareness about the severity of Delhi’s air pollution.

In 2017, India attempted to attack vehicular pollution by implementing Bharat Stage IV (BSIV) vehicular emission norms nationwide. However, this proved insufficient in the face of growing sources of pollution. Meanwhile, solid waste burning and unregulated construction activities continued unabated.

Despite these efforts, Delhi's pollution levels remain dangerously high, especially during winter. Experts attribute this to a combination of factors, including weak regulation enforcement, gaps in public transport infrastructure, and economic pressures on farmers leading to continued stubble burning.

In its December 20, 2021 issue, Where Stars Don’t Shine, Outlook explored the issues surrounding Delhi’s pollution problem in depth. Ashutosh Sharma wrote about how efforts to curb the city’s declining air quality should not be limited to only the winter months but also need year-long attention. Aditya Dubey traced how the city’s youth were rising against political inertia and leading the fight for cleaner air. And Bharati Chaturvedi highlighted how the crisis affected underprivileged children the worst. 

You can read more from the issue.