In Mumbai, PM2.5 shot up between 2019 and 2020 by 54.2 per cent.
The air quality in Mumbai in October has undergone a steady decline in the last five years, and even in Delhi, the situation is no better, a study has found. October is the first of the winter months when air quality starts going south, and in Mumbai, the volume of pollutants has doubled between 2019 and 2023.
A report by climate-tech start-up Respirer Living Sciences found Delhi, Mumbai, Hyderabad and Kolkata all exhibiting a rise in highly polluting PM (Particulate Matter) 2.5.
In Mumbai, PM2.5 shot up between 2019 and 2020 by 54.2 per cent, and after a marginal drop in 2021 (by 3 per cent) and 2022 (by 0.9 per cent), spiked again in 2023 by 42.1 per cent.
The city authorities have drawn up a detailed plan to combat pollution, fitting vehicle-mounted air filters on 350 BEST buses, setting up virtual chimneys at traffic congestion spots, placing special streetlights and installing air purification systems in select gardens.
The city has also ordered 30 vehicles mounted with sprinklers and industries have been asked to increase the height of chimneys.
Delhi saw a sharp rise in PM 2.5 levels between 2019 and 2020 (by 32 per cent), a dip in 2021 (by 43.7 per cent), and a steady increase in 2022 and 2023 - though the peak pollution season expected to begin with Diwali is still some way off.
Air quality in some parts of the city has dropped to the "severe" category and is expected to remain "very poor" for a few more days.
In Hyderabad, PM 2.5 increased between 2019 and 2020 by 59 per cent, dipped by 2.9 per cent in 2021 and shot up by 29.1 per cent in 2022. This year, it spiked by 18.6 per cent.
Kolkata, though, bucked the trend somewhat, with PM 2.5 levels dipping between 2019 and 2020 (by 26.8 per cent), going up in 2021 by 51.7 per cent. It dropped in 2022 by 33.1 per cent but rose again this year by 40.2 per cent.
Four state capitals, unexpectedly, showed a drop in PM2.5 levels this year compared to the last - Lucknow, Patna, Bengaluru and Chennai.
The biggest drop took place in Chennai (23.7 per cent) followed by Bengaluru (11.6 per cent), Patna (11.1 per cent) and Lucknow (0.9 per cent).
On Tuesday, expressing concern over the deteriorating air quality, the Supreme Court asked Delhi and four neighbouring states -- Punjab, Haryana, Uttar Pradesh and Rajasthan -- to submit a report on the steps taken to curb pollution.
Stubble burning in Punjab and Haryana is a major source of pollution in the northern states.
On Sunday, Punjab saw a 740 per cent increase in farm fires. Across the state, 1,068 fires were reported -- the highest in a single day in the current harvesting season - which was even caught in satellite pictures.