Delhi records cleanest October air in 4 years as heavy rain brings temperature to 20.7°C

Delhi recorded its cleanest October air in four years on Friday after an unusual spell of heavy rainfall washed away pollutants, while temperatures plunged to their lowest October levels in records dating back to 1951.

The national capital's Air Quality Index (AQI) dropped to 60, placing it in the 'satisfactory' category, according to the Central Pollution Control Board's (CPCB) 4pm bulletin. The reading marked a dramatic improvement from Thursday's AQI of 222, which was in the 'poor' category.

The city also experienced an unusually cold day, with the maximum temperature at Safdarjung, Delhi's base weather station, settling at 20.7°C. This was 10.3 degrees below normal and broke the previous record for the lowest October maximum temperature of 21.5°C, registered on October 25, 1975.

The India Meteorological Department (IMD) recorded a minimum temperature of 17.2°C, which was 1.1 degrees above normal.

Rainfall brings unprecedented improvement in air quality

The sharp improvement in Delhi's air quality followed widespread rainfall triggered by the interaction of Cyclone Arnab with a western disturbance. The latter is a weather system that carries moisture from the west and often brings rain and thunderstorms to northern India.

Safdarjung received 61.4mm of rainfall in the 24 hours ending at 8.30am on Friday, making it the sixth-highest 24-hour October rainfall recorded at the station since 1951. The observatory recorded an additional 4.2mm between 8.30am and 5.30pm.

Other weather stations across the city also registered substantial rainfall. Palam received 43.1mm in the 24 hours ending at 8.30am, followed by another 3mm by 5.30pm. Lodhi Road recorded 67.4mm by 5.30pm, while Ridge and Ayanagar received 52.2mm and 57.5mm, respectively.

Mahesh Palawat, vice-president of meteorology and climate change at Skymet Weather, attributed the unusual spell of unsettled weather across northern and eastern India to the convergence of multiple weather systems.

These included a western disturbance over the western Himalayas extending towards Jammu, an induced cyclonic circulation over southern Punjab and a depression over North Chhattisgarh. Together, they contributed to a substantial influx of moisture, he said.

The India Meteorological Department had also forecast further spells of rain and thunderstorms across Delhi-NCR on Friday, with conditions expected to improve over the weekend.

October AQI average set to break previous record

Friday's AQI of 60 represented a decline of 162 points from Thursday's reading of 222, making it the fourth-largest single-day fall recorded for an October day since the CPCB began issuing daily AQI bulletins in 2015.

It was also Delhi's cleanest air day since September 28, when the AQI stood at 56, also in the 'satisfactory' category.

The improvement has put October 2026 on course to become the cleanest October since the CPCB began its daily AQI records. The average AQI for the first 30 days of the month stood at 167, already below the previous best monthly average of 173 recorded in October 2021.

For comparison, Delhi's average AQI stood at 210 in October 2022, 219 in 2023, 223 in 2025 and 234 in both 2019 and 2024. In the other years between 2015 and 2020, the monthly average ranged between 264 and 285.

The improvement is particularly significant given the city's historical October pollution levels. Before Friday, Delhi had recorded an AQI of 60 or below on just five October days since 2015. These included October 18, 2021, when the AQI was 46, and October 7, 8, 9 and 10, 2022, when the readings were 55, 56, 48 and 44, respectively.

Both earlier spells of cleaner air coincided with substantial rainfall. Safdarjung received 87.9mm of rain on October 18, 2021, and 74.3mm on October 9, 2022.

Friday's reading was also the lowest AQI recorded for October 30 since the CPCB began its daily bulletins. Between 2016 and 2025, the AQI on this date had ranged between 268 and 431.

October 2026 will retain its position as the cleanest October on record unless Saturday's AQI rises to 352 or higher, which would represent a jump of nearly 300 points in a single day.

Under CPCB's classification, an AQI between 0 and 50 is considered 'good', 51 and 100 'satisfactory', 101 and 200 'moderate', 201 and 300 'poor', 301 and 400 'very poor', and 401 and 500 'severe'.

Lowest October maximum temperature since 1951

The maximum temperature of 20.7°C recorded at Safdarjung on Friday was the lowest for any October day in the station's records dating back to 1951.

The previous lowest was 21.5°C, recorded on October 25, 1975. Other notably low October maximum temperatures included 21.9°C on October 31, 1961, 22.1°C on October 18, 1971, and 22.2°C on October 1, 1954.

The rainfall figures also placed October 2026 among the wettest months recorded at Safdarjung.

With the latest spell, the station's cumulative rainfall for the month reached 123.3mm, making it the fourth-wettest October since 1951. The total has surpassed the 122.5mm recorded in October 2021.

The wettest October at Safdarjung was in 1954, when the station received 238.3mm, followed by 236.2mm in 1956 and 128.6mm in 2022.

Despite the substantial rainfall this year, the station's highest-ever 24-hour October rainfall remains 172.7mm, recorded on October 1, 1954. The second-highest was 110.9mm on October 9, 1956.

The other three highest 24-hour rainfall totals were 87.9mm on October 18, 2021, 74.3mm on October 9, 2022, and 68.3mm on October 3, 2004.

Weather conditions expected to improve over the weekend

With the weather systems weakening and moving away, Delhi is expected to see a gradual rise in daytime temperatures.

Palawat said maximum temperatures were likely to climb towards 29-30°C from Saturday, bringing a noticeable improvement in daytime weather conditions.

The IMD forecast partly cloudy skies over the capital during the weekend, with mainly clear conditions expected from November 2. Maximum and minimum temperatures on Saturday were expected to settle around 24°C and 16°C, respectively.

However, the improvement in air quality may not last. The Air Quality Early Warning System has forecast a deterioration in Delhi's AQI to the 'poor' category on Sunday, with pollution levels expected to remain in the 'poor' and 'very poor' categories over the following days.

The rainfall has nevertheless provided the capital with a temporary respite from its October pollution, while delivering an unusual combination of record-low daytime temperatures and one of the month's heaviest rainfall spells in more than seven decades.