Delhi’s air quality in May this year was the cleanest for the month in over a decade, excluding 2020 and 2021, when a lockdown was imposed. The monthly average air quality index (AQI) stood at 170, placing it within the “moderate” category according to the Central Pollution Control Board (CPCB) classification.This represents a significant shift from the usual trend, where May has consistently recorded “poor” average air quality in most years between 2015 and 2024. The air quality improvement this May was largely driven by meteorological factors. The combination of frequent rain, gusty winds, and the absence of prolonged dry spells contributed to lower pollutant concentrations near the surface, as per officials.An analysis of AQI data from the CPCB for May from 2015 to 2025 reveals that May typically sees a high number of days where AQI is “poor” (between 201 and 300) or “very poor” (between 301 and 400). For instance, in 2015, 2016, and 2017, there were 24 to 25 such days each May (see box).Even in recent years, such as 2022 and 2024, there were 21 and 20 days, respectively, in these higher pollution categories.In contrast, May 2025 recorded only five “poor” days and no “very poor” days. However, there were no “satisfactory” days recorded either. This marks the lowest number of high pollution days in May since 2020 and 2021, when lockdown-related restrictions resulted in significantly reduced emissions and cleaner air.The improvement in air quality during May this year coincided with unusual weather marked by high rainfall and frequent storm systems.According to the India Meteorological Department (IMD), Delhi received 186.4 mm of rainfall, the highest ever recorded for the month in the city.Story continues below this adThe monthly rainfall exceeded the average of 30.7 mm and broke the previous record of 165 mm set in 2008. The month saw four “rainy days” as defined by IMD as days with rainfall exceeding 2.4 mm. Multiple low-pressure zones, western disturbances, along with associated squalls and thunderstorms, led to frequent rain and strong surface winds, which helped disperse accumulated pollutants in the atmosphere.CPCB’s day-wise data shows that most days in May 2025 had AQI values in the moderate (101–200) or poor (201–300) range. The few days classified as “poor” were linked to dust storm events that raised PM10 and PM2.5 concentrations, particularly around 16-17 May and 20-22 May.On May 15, Delhi-NCR woke up to a thick haze — reminiscent of the winter pollution months — after dust-laden winds from North Pakistan travelled through Rajasthan, Punjab, and Haryana and shrouded the region overnight. A massive dust storm with winds blowing up to 80 kmph followed by heavy rain also hit the region on the evening of May 22.Unlike May 2022 and 2023, this year saw no official heatwave days in Delhi. The month’s average maximum temperature was 37.6°C, and the average minimum temperature was 25.3°C, according to IMD data. Even as there were days with high humidity and elevated “feels like” temperatures soaring to 50°C, the presence of cloud cover and regular rain spells has kept daytime temperatures in check.Story continues below this adMeanwhile, the month ended with rainfall and a thunderstorm. The sudden change in weather led to a sharp drop in temperatures and an increase in wind speeds across Delhi and surrounding regions on Saturday evening.According to the Met Office, temperatures fell significantly between 3:15 pm and 4:45 pm at multiple locations in Delhi. The largest temperature drops were recorded at Delhi University (8.4°C), Pitampura (8.3°C), and Ayanagar (8.1°C), with several other stations such as Najafgarh, Palam, and Narayana registering declines between 7°C and 7.8°C. Safdarjung, the city’s official observatory, reported a 6°C drop during this period.The thunderstorm was accompanied by strong surface winds. The highest wind speeds were recorded in Jind (63 km/h), Rohtak (61 km/h), and Palam (56 km/h), while other locations like Sonipat, Najafgarh, and Pragati Maidan saw gusts between 46 km/h and 50 km/h. Safdarjung reported a peak wind speed of 40 km/h. The IMD had issued an orange alert for parts of North Delhi and Southwest NCR earlier in the day, forecasting thunderstorms, dust storms, light to moderate rainfall, and winds ranging from 50 to 60 km/h. The storm helped suppress temperatures and briefly lifted dust, but widespread rainfall and gusty conditions limited a rise in pollution levels later in the day.The IMD has forecast that temperatures in Delhi for the first week of June will range between 25°C and 39°C, with partly cloudy skies and the possibility of light rainfall. No weather alerts have been issued as of 1 June.