Which Delhi air myths don't hold up?

Four claims come back every winter. Each has a grain of truth, and each collapses when you look at the numbers.

Do houseplants clean indoor air?

Not measurably, at any number of plants a home could hold.

The idea traces to a 1989 NASA technical memorandum by B. C. Wolverton and colleagues, Interior Landscape Plants for Indoor Air Pollution Abatement, which studied how plants and their soil might remove indoor pollutants and proposed a plant-based air filter.¹ The experiments behind this line of research were run in sealed test chambers, nothing like a ventilated room.²

In a 2020 review, Bryan Cummings and Michael Waring converted 196 results from 12 such chamber studies into a common measure, the clean air delivery rate. The median plant cleaned about 0.023 m³ of air per hour. To match the cleaning that ordinary air exchange with the outdoors already provides in a typical building, they estimated you would need 10 to 1,000 plants per square metre of floor.² The review dealt with volatile organic compounds, gases rather than particles.

Do smog towers clean the air?

Only very close to the tower, and the effect fades within a few hundred metres.

Delhi built large smog towers at Connaught Place and Anand Vihar. In an affidavit to the National Green Tribunal in November 2023, the Delhi Pollution Control Committee said they had little effect on the air around them. As reported by Down To Earth, an IIT Bombay assessment found reductions of 48–56% within 20 m of a tower, falling to 12–13% at 109–199 m; an IIT Delhi assessment found 13–15% within 200 m.³ The DPCC estimated that at least 40,000 towers would be needed to cut the city's pollution by 17%.³

The arithmetic is the point. Delhi covers about 1,483 km²,³ and its air is constantly replenished from upwind; a machine can clean a pocket of it, not the whole.

Is Delhi's winter pollution only stubble burning?

No. Stubble matters a great deal on some days and not at all on others.

Estimates put stubble's share of Delhi's PM2.5 in November 2024 at about 20% on average, peaking at 38%.⁴ In November 2025 its share fell to about 7%, yet the city's average PM2.5 that month was 215 µg/m³, roughly double October's.⁴ In December 2025, with stubble's share near zero, Delhi's PM2.5 averaged 210 µg/m³.⁵ Take stubble away entirely and the winter problem remains, because the weather that traps Delhi's own and the region's emissions remains. The chapters on sources and winter explain why.

The opposite myth, that stubble doesn't matter, is also wrong: IIT Kanpur's study found a distinct November surge of biomass-burning particles traced to crop fires in Punjab and Haryana.⁶

Does rain fix Delhi's air?

For a day. Sustained clean air comes with the monsoon season, not with a single storm.

The monsoon reached Delhi on 28 June 2024, according to the IMD as reported that day.⁷ Safdarjung recorded 228.1 mm of rain in the 24 hours to 8:30 am, the heaviest June day in Delhi since 1936.⁸ The bulletin AQI fell from 136 on 26 June to 79 on 27 June and 64 on 28 June; on 29 June it was back to 118, Moderate.⁹

What does keep the air cleaner is the whole monsoon pattern: July and August 2024 averaged an AQI of 84, the best two months of the year.⁹ Summer air also flushes out four to six times faster than winter air.¹⁰ A winter shower washes some particles out, but it does not change the stagnant weather that let them build up.