New Delhi, India – Delhi recorded its most polluted monsoon period in seven years, with the average Air Quality Index (AQI) between July and September reaching 105, the highest for this period since 2019. The analysis, conducted by the Centre for Research on Energy and Clean Air (CREA), indicates a significant deterioration in air quality despite slightly above-normal rainfall during the season.
Information was available with The Chenab Times indicating that the monsoon season, spanning approximately 84 days, saw Delhi experience one day with ‘good’ AQI, 49 days of ‘satisfactory’ air quality, 39 ‘moderate’ days, and two ‘poor’ days. The average AQI of 105 during July-September was marginally lower than the 2019 average of 106.
The analysis further revealed that among the two primary particulate pollutants, PM10 was more dominant this year. Its average concentration stood at 108 micrograms per cubic metre, marking the highest since 2019 when it was 109 micrograms per cubic metre. PM2.5 averaged 37 micrograms per cubic metre, a level not seen since 2024, though it remained below the averages recorded in 2023 (39 micrograms per cubic metre) and 2019 (40 micrograms per cubic metre).
Manoj Kumar, a representative from CREA, informed PTI that the increase in PM10 levels, even with rainfall exceeding the average, points to dust and coarse particles playing a crucial role in the seasonal pollution. He stated that Delhi experienced its worst monsoon air quality since 2019, with both the average AQI and PM10 levels reaching their highest in this period. Kumar attributed the sharp rise in PM10 to dust and other coarse particles, suggesting that dry spells interspersed with rainfall, along with local weather conditions, likely facilitated pollution build-up between precipitation events.
Previous years saw varying AQI averages during the July-September period. In 2024 and 2025, the average AQI was 91, followed by 103 in 2023, 95 in 2022, 99 in 2021, and 88 in 2020. The rise in PM10 concentrations was particularly notable in recent years, with averages recorded at 88 micrograms per cubic metre in 2025, 87 in 2024, 105 in 2023, 92 in 2022, 98 in 2021, and 85 in 2020. Conversely, PM2.5 averages were 32 micrograms per cubic metre in 2025, 37 in 2024, 39 in 2023, 36 in 2022, 37 in 2021, and 35 in 2020.
The monsoon onset over Delhi this year occurred on July 2, five days later than the normal date of June 27, marking the first July onset in five years. The withdrawal took place on September 23, two days earlier than the typical withdrawal date of September 25. In comparison, the monsoon in 2019 arrived on July 5 and withdrew on October 10, lasting 97 days, significantly longer than the current year’s monsoon spell. During the July to September period in 2019, Delhi registered two ‘good’ AQI days, 51 ‘satisfactory’ days, 34 ‘moderate’ days, four ‘poor’ days, and one ‘very poor’ day.
Despite a shorter duration, Delhi received 728.6 mm of rainfall during this monsoon season, exceeding the normal precipitation of 629.7 mm by nearly 16 per cent. An official from the India Meteorological Department (IMD) had previously informed PTI that while rainfall was above average, no significant rainfall records were broken, noting that Delhi had experienced over 900 mm of rainfall in each of the two preceding years.
A separate study conducted by the Centre for Science and Environment (CSE) analysed the monsoon period from June to August, finding that the respite from pollution during rainy spells was often transient. The study indicated that PM2.5 levels would rapidly increase once the rain ceased. During six distinct rainy spells observed by CSE, average PM2.5 levels decreased from 40.6 micrograms per cubic metre before the rain to 32.7 micrograms per cubic metre during the rain. However, levels climbed to 36.2 micrograms per cubic metre the day after the rain and further to 45.1 micrograms per cubic metre two days later, surpassing the pre-rain levels.
The CSE study also highlighted that even during the monsoon, Delhi managed only one ‘good’ AQI day across the 92 days analysed. The majority of days fell into ‘moderate’ (53 days) and ‘satisfactory’ (35 days) categories, with three days being classified as ‘poor’. Notably, even the season’s heaviest rainfall event on August 8, which saw average rainfall of 101.05 mm at Safdarjung and Palam, only resulted in Delhi’s AQI being in the ‘satisfactory’ category.
The CSE analysis reported average PM2.5 levels of 40.2 micrograms per cubic metre during the June-August monsoon period, representing an approximate 33 per cent decrease from the 60.2 micrograms per cubic metre recorded during April-May. However, this improvement proved temporary as continuous emissions from vehicles, industries, waste burning, and power generation contributed to the pollution load once the rains subsided.
Furthermore, the study indicated that the monsoon pollution was not solely attributable to particulate matter. As PM2.5 levels declined, gaseous pollutants emerged as significant contributors to the daily AQI on multiple occasions. Ground-level ozone was identified as the prominent pollutant on 20 per cent of monsoon days, followed by nitrogen dioxide on 10 per cent and carbon monoxide on seven per cent of the days. These findings suggest that while the monsoon can temporarily cleanse Delhi’s air of particulate pollution, it does not mitigate the underlying emissions that continually rebuild the pollution load between rainfall events.
With the monsoon officially withdrawing on September 23, Delhi has now entered the post-monsoon phase. This period is characterized by the cessation of regular rainfall’s cleansing effect, creating conditions more conducive for pollution accumulation.
The Chenab Times News Desk