Delhi Records Poorest August Air Quality In Three Years, Despite Above-Normal Monsoon Rainfall
Environmental experts argue that Delhi's air-quality management must address pollution sources year-round, not just in winter | Surabhi Gupta reports.
Published : September 1, 2026 at 5:57 PM IST
|Updated : September 1, 2026 at 6:02 PM IST
New Delhi: Delhi's air quality deteriorated unusually in August 2026 despite the capital receiving above-normal monsoon rainfall, with Central Pollution Control Board (CPCB) data indicating that the month recorded its poorest August air quality in three years.
According to an analysis of CPCB's daily air-quality data, Delhi's monthly average AQI stood around 92, compared with 89 in August 2025 and 72 in August 2024. The city did not record a single day in the "Good" category, while 19 days were classified as "Satisfactory" and 11 as "Moderate".
The deterioration became more pronounced towards the end of the month, with AQI readings in Delhi and the National Capital Region (NCR) moving into the "Poor" range and crossing 200 at several points between August 27 and 31.
The trend is particularly significant because August is generally considered one of Delhi's cleaner months due to the monsoon, when rainfall and winds wash pollutants out and improve atmospheric dispersion.
However, experts said surplus rainfall alone does not guarantee clean air, particularly when rain is unevenly distributed and atmospheric conditions remain stagnant.
Former UN Climate Technology Centre and Network Advisory Board member and environmentalist Soumya Dutta told ETV Bharat, "Delhi had an above-average air pollution level in August 2026, despite having a much higher than average rainfall month; the Safdarjung station recorded a monthly rainfall of 354.1 mm compared to an average of 222.9 mm. This should have made Delhi air cleaner than average, yet the average AQI was close to 100."
He, however, pointed out that the picture was more complicated, noting that 19 days in August were classified as "Satisfactory" under CPCB norms, with many of those days coinciding with good rainfall.
Why Did Rain Fail To Clean Delhi's Air?
Dutta said the apparent paradox highlights the persistence of Delhi's internal pollution sources. He said, "Delhi's internal air pollution sources are stubbornly persistent: Over a crore internal combustion vehicles, millions of kitchens, widespread garbage burning, waste-to-energy plants. The moment the cleansing rains and winds stop, the pollution comes back and hangs thick."
According to him, weak winds were another major factor. Even when rain temporarily removed pollutants, the absence of strong winds meant that emissions generated within the city and surrounding region could not disperse effectively.
The third factor was high relative humidity and increased water vapour, which can contribute to the formation and growth of particulate pollution through atmospheric chemical processes.
Dutta also highlighted unusually warm nights. The average minimum temperature at Safdarjung was 26.8°C in August, which he said was the highest since 2018, barring 2023.
Higher night-time temperatures can influence atmospheric stability and vertical mixing, potentially preventing pollutants from dispersing upwards.
Dutta added that transboundary pollution from 11 coal-based power plants in nearby states could also have contributed to Delhi's elevated pollution levels.
Rainfall Was Surplus, But Unevenly Distributed
Climate scientist and visiting faculty at TERI School of Advanced Studies, S N Mishra, said August's pollution levels demonstrate why rainfall and air quality cannot be viewed in isolation.
"Delhi's poor air quality in Aug is a clear reminder that rainfall alone does not guarantee clean air. Although Delhi received surplus rainfall, its distribution was highly uneven, with only a few heavy rainfall episodes. For much of the month, conditions remained conducive to pollution accumulation, and the AQI stayed close to 100," Mishra said.
He said wind conditions were particularly important, not just over Delhi but across the wider NCR region.
According to Mishra, Rajasthan remained largely dry during parts of the month, while sections of Punjab also experienced relatively dry conditions. Frequent north-westerly winds could therefore transport dust and other pollutants towards Delhi-NCR. Weak monsoon circulation and relatively dry conditions to the west also reduced the effectiveness of natural dispersion.
"Added to this is the persistent problem of local emissions, particularly vehicular tailpipe emissions, dust and other urban sources. These emissions continue irrespective of rainfall and can quickly build up when atmospheric ventilation is poor," he said.
Mishra said the August experience showed that "rain surplus" and "clean air" are not synonymous.
"What matters is the timing, intensity and spatial distribution of rainfall, along with wind speed and direction and the overall regional atmospheric circulation," he said.
He warned that as Delhi moves towards the post-monsoon and winter seasons, pollution-control efforts will have to become more focused and regionally coordinated.
Humidity, Stagnant Air Add To Pollution Burden
Shailender Kumar, environmentalist and academic councillor at IGNOU, Delhi, described the August episode as a case of meteorological conditions overriding rainfall's usual cleansing effect.
"What we're seeing in August 2026 is a textbook case of meteorology overriding rainfall's usual cleansing effect," Kumar said.
He explained that high relative humidity can encourage hygroscopic growth of particulate matter, under which fine particles absorb moisture and increase in size. This can contribute to haze and affect visibility.
"When you combine this with weak wind speeds, you get poor horizontal dispersion: pollutants from vehicles, construction dust and other local sources simply aren't carried away; they accumulate in a shallow, stagnant boundary layer close to the surface," he said.
Kumar also pointed to the absence of "Good" air-quality days despite above-normal rainfall as evidence that precipitation alone cannot compensate for poor atmospheric ventilation.
He said the deterioration towards the end of August, when AQI readings crossed 200, suggested that the stagnant conditions had intensified.
The expert argued that Delhi's pollution-control system should not focus exclusively on winter pollution episodes.
"Delhi's pollution management architecture, largely built around winter inversion episodes, needs a parallel early-warning and response mechanism for monsoon-season stagnation events," Kumar said.
He suggested monitoring wind-speed and humidity thresholds in real time, allowing authorities to activate dust suppression and traffic-control measures before air quality reaches the "Poor" category.
'Rain Cannot Solve A Year-Round Pollution Problem'
Environmental scientist Hishmi Jamil Husain said August's deterioration was particularly surprising because the month is normally expected to provide Delhi with relief from pollution.
"August is usually the month when we expect the monsoon to give Delhi some relief. But this year, the opposite happened. Delhi recorded its worst August air quality in three years," Husain said.
He said the key issue was that rain was only one component of the atmospheric system.
"When winds are weak and humidity is high, pollutants from traffic, road dust, construction and other local sources can remain trapped close to the ground. By the last few days of August, AQI in Delhi and parts of NCR had crossed 200," he said.
Husain stressed that the city cannot rely on the monsoon as a natural pollution-control mechanism.
"Rain may wash pollutants out temporarily, but it doesn't stop the sources that keep putting them back into the atmosphere," he said.
He also called for Delhi-NCR to be treated as one connected airshed, arguing that pollution does not respect administrative boundaries.
"We need to think of Delhi-NCR as one connected airshed, with year-round action on transport, dust, construction, industry and regional emissions," Husain said.
Geospatial and disaster management expert Rajesh Paul also said the August episode showed the limitations of relying on rainfall alone.
"What is unusual about Delhi this August is that the deterioration in air quality has happened despite above-normal monsoon rainfall. Rain normally helps wash pollutants out of the atmosphere, but rainfall alone cannot guarantee clean air," Paul said.
He said high humidity and weak surface winds allowed emissions from vehicles, road dust, construction and other urban sources to remain trapped close to the ground.
Paul said the worsening air quality toward the end of August warned that Delhi's pollution problem could no longer be treated as exclusively a winter phenomenon.
"This shows that Delhi's pollution problem is not only a winter phenomenon, it is also increasingly becoming a year-round urban air-quality challenge," he said.
He called for continuous emission-control measures rather than relying primarily on emergency action during the winter months.
IQAir Data Also Points To Persistent Pollution
Delhi ranked seventh among the world's most polluted major cities on Tuesday, according to real-time data from Swiss air-quality monitoring platform IQAir.
As per the IQAir live major city ranking at 9-10 am on September 1, 2026, Delhi recorded an AQI of 152, placing it in the "Unhealthy" category.
India's national annual average PM2.5 concentration was reported at 48.9 micrograms per cubic metre, nearly 10 times WHO's annual guideline of 5 micrograms per cubic metre.
Experts said the August experience could become increasingly important as the monsoon retreats and Delhi enters the post-monsoon period.
With September marking the transition towards weaker monsoon conditions, atmospheric ventilation could become more critical. Historically, Delhi's pollution burden rises sharply from October through January as winds weaken and winter atmospheric conditions increasingly trap emissions.
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