For some days in early July, the city of Delhi got some of the best skies that it had witnessed in almost three years—"good"" quality air. The rain brought in by monsoon showers had cleansed the sky of all pollutants, and the citizens of the capital woke up to a low air quality index. However, as predicted by the experts, the respite was only temporary. In a matter of days, a sudden monsoon break along with the arrival of a cloud of mineral dust from West Asia had once again made Delhi’s air quality reach “poor” and “hazardous” levels.
It is hard to believe the change even in Delhi’s unstable environment. A few days ago, heavy rains helped bring the AQI levels in Delhi to 48, marking the lowest levels in the city so far in 2026 and being the first time in nearly three years that the AQI level came down to the 'good' level in the Commission for Air Quality Management (CAQM)'s categorization. The meteorological explanation for the same was primarily due to wet deposition and below-cloud scavenging—the phenomenon wherein falling raindrops colliding with particulate matter drag them down to the ground, and wind disperses whatever little pollution may be left.
But then things turned around. With the shift of the monsoon trough northwards towards the foothills of the Himalayas, the rains in Delhi as well as the Indo-Gangetic Plain region went into hibernation for some seven days, when dust started coming in.
Strong winds started blowing mineral particles from storms that have been happening in Afghanistan, Iran, and Pakistan into north-western parts of India. This is something that is referred to as trans-national dust transport by authorities. This situation led to an increase in levels of PM10, which are coarse particulate matter that comes from soil and road dust.
The weekend saw Delhi's AQI rise to 261, making it the highest value that had been seen for the last 85 days. It was also the highest AQI value since April 17, taking the city into the “poor” category. Conditions went on to deteriorate for a few more days, hitting 293 amid dusty and strong wind conditions. The most extreme level witnessed was an hourly AQI (US) at 467, which was “hazardous.” The conditions later improved somewhat, with the AQI oscillating between “moderate” and “poor.”
The main cause of this occurrence is certainly not traffic and construction in the area but weather, which acts as a medium that distributes dust produced thousands of kilometers away. The CAQM has directly blamed the poor condition of air quality in Delhi-NCR on the wind currents carrying dust created by storms that occur in countries like Afghanistan, Iran, and Pakistan.
This dust then moves through Pakistan into northwest India and settles in the Indo-Gangetic plain, the most polluted air basin in the world.
This situation is aggravated by another effect, which is more localized in nature. Generally, in Delhi, the windy conditions are pollution fighters because these help in dispersing the emissions that are produced in the city through exhaust, dust, and industrial emissions. However, in the current case, wind is playing the role of polluter by bringing foreign pollution into the city and lifting the already settled pollution from the city’s roads and open spaces.
The dry condition of the roads, where the rains have failed to come in, facilitates the process of resuspension.
The CAQM has stated that it expects the air quality of Delhi to stay in the "poor" category in the coming days, and the improvement will depend upon the ending of the spell of transnational dust and hopefully rains.
Significantly, stage one restrictions of the Graded Response Action Plan have not been imposed for this particular case, as it is considered temporary in nature.
Delhi’s pollution crises, in the minds of the people, are linked exclusively with the winter months of the year due to the burning of agricultural waste in the neighboring states of Punjab, Haryana, Rajasthan, and Uttar Pradesh during the winter, along with favorable wind conditions and temperature inversion leading to smog formation. However, this episode of pollution is quite unique because of both its cause and duration.
The reason behind this phenomenon has been the presence of a temporary meteorological coincidence of dust winds along with a pause in the monsoon rainfall.
Nevertheless, there is still an important message in this incident that environmental experts have been stressing all through this monsoon season: although rainfall may create a big impact, it remains "a rinse rather than a remedy," according to another group of experts. The root causes of pollution in the city of Delhi, which include vehicle emissions, industries, construction dust, biomass and waste burning, as well as diesel generators, do not go away once it starts raining or the wind changes its course. They only get covered up temporarily until the favorable weather changes.
The point is stressed by the public health experts that any short-term reduction in the exposure to PM2.5, even though it is limited to a period of a few hours or days, is very beneficial for those who are most sensitive: children, the elderly, and those suffering from respiratory or cardiovascular diseases.
At the same time, they make the point that this is going to remain a temporary relief without further policy measures.
