Delhi records lowest May PM2.5 levels since 2015, but PM10 levels remain steady
The cleaner PM2.5 levels also coincided with favourable weather conditions during the month.
The divergence between the two pollutants is significant because PM2.5 and PM10 often respond differently to meteorological conditions, experts say. Delhi recorded its lowest PM2.5 levels in May this year in at least a decade. However, PM10 levels logged in May remained almost unchanged from May 2025. This sharp contrast between the concentration of two pollutants, experts say, suggests that rain and winds may have temporarily cleared finer pollutants without tackling the coarser particles from sources that generate them.
Data from the Central Pollution Control Board (CPCB) show that Delhi’s average PM2.5 concentration in May this year stood at 54 µg/m³ (micrograms per cubic metre), the lowest in May since at least 2015 and nearly half the 114 µg/m³ recorded in May 2017. PM10 levels, in contrast, averaged 175 µg/m³, marginally higher than 173 µg/m³ in May 2025 and only slightly lower than the 185 µg/m³ recorded in May 2023.
The divergence between the two pollutants is significant because PM2.5 and PM10 often respond differently to meteorological conditions, experts say. PM2.5 particles are lighter and remain suspended in the atmosphere for longer periods, making them more susceptible to dispersion by strong winds and washout during rainfall events. PM10, which includes coarser dust particles, tends to be less responsive and is more closely linked to dust resuspension, construction activity, and regional dust transport.
Last year in May, Delhi logged substantially higher rainfall (185.9 mm) and a lower average maximum temperature (37.6°C) compared to this May. Yet despite the difference in weather conditions, PM10 levels this May still remained almost identical to those of May 2025, revealing the persistence of coarse-particle pollution. PM2.5 levels, however, fell from 67 µg/m³ in May 2025 to 54 µg/m³ this year.
The cleaner PM2.5 levels also coincided with favourable weather conditions during the month. According to India Meteorological Department (IMD) data, Delhi received 19.5 mm of rainfall across three rainy days in May, with precipitation recorded during the opening week and again towards the end of the month.
Delhi recorded an average maximum temperature of 39.5°C in May, marking only a small variation from the 40°C the capital usually logs for the month. Meanwhile, the average minimum temperature stood at 25.8°C. The city saw only one heatwave day this May, compared with six in May 2024, when the average maximum temperature reached 41.7°C. Delhi had recorded no heatwave days in May last year.
“PM2.5 has been the lowest this year largely because of meteorological conditions which included sustained winds and rainfall. The last few days have seen rain, and there were rainy spells even in the beginning of the month,” said Sunil Dahiya, lead environmental analyst and founder of Envirocatalysts, a Delhi-based think tank.
“There is a declining trend in PM2.5, but we cannot say that it is because emissions at source have reduced. What we are seeing is better dilution of pollutants and washout due to rainy days. PM10 levels have remained relatively high, which suggests that only the finer particles were dispersed temporarily because of weather conditions, rather than there being a substantial reduction in emissions,” he added.
The city also recorded relatively low ozone levels during this May. CPCB data show average ozone concentrations of 53 µg/m³, among the lowest levels observed since 2019 and well below the levels exceeding 100 µg/m³ seen in several May months in past years. However, Dahiya said there is not enough evidence yet to attribute this to any particular factor.
“One possibility is that petrol and diesel consumption may have gone down because of the West Asia crisis, but we cannot say that for certain at the moment. Data from the Ministry of Petroleum would be required to establish that, which would be released soon,” he said.
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