Mumbai air pollution is entering the post-monsoon season under a combination of conditions that can make the city’s existing emissions harder to disperse. An early withdrawal of the southwest monsoon from Maharashtra, rainfall deficit across 21 districts, dry winds carrying dust and the influence of a strong El Niño are converging just as the city’s Air Quality Index has begun to deteriorate.
The immediate change was visible at the beginning of October. Mumbai’s AQI remained in the “good” category, between 0 and 50, until September 29, according to the report. It rose sharply in October and crossed 100 on October 2. The deterioration coincided with the withdrawal of rain-bearing winds, which normally help remove or settle pollutants from the atmosphere.
This is not simply a story about weather. It reveals how Mumbai’s air quality depends on the interaction between atmospheric conditions and everyday urban activity. Vehicular emissions, industrial pollution, construction dust, debris, open waste burning and traffic congestion remain present regardless of the season. Rainfall can temporarily suppress some of these pollutants. When rain retreats early and dry conditions persist, the same emissions operate in a less favourable atmospheric environment.
The India Meteorological Department’s declaration of monsoon withdrawal from Maharashtra provides the seasonal trigger. The report describes it as Mumbai’s earliest monsoon withdrawal since 2023. At the state level, 21 districts recorded deficit rainfall, while the Maharashtra government declared a drought in 265 of the state’s 358 talukas last week. These figures establish a wider dry-weather context for the city, even though Mumbai’s pollution is also shaped by local sources and coastal atmospheric conditions.
El Niño adds another layer to that context. It is the warm phase of the El Niño-Southern Oscillation, associated with changes in sea-surface temperatures and atmospheric conditions in the eastern Pacific Ocean. The phenomenon can alter weather patterns across regions and has historically been associated with below-average southwest monsoon conditions in India. In the material supplied for this report, experts connect strong El Niño conditions with reduced rainfall, increased dryness and a greater likelihood that pollutants will remain in the atmosphere.
Raghu Murtugudde, Emeritus Professor at the University of Maryland and visiting professor at IIT Kanpur’s Kotak School of Sustainability, attributed the recent AQI deterioration partly to clockwise wind circulation. He said this circulation was bringing dry and dusty air from Rajasthan, Pakistan and the Middle East. According to Murtugudde, sinking air under such circulation can trap pollutants rather than allowing them to disperse.
Murtugudde also pointed to the relationship between particulate composition and the changing weather pattern. PM10 levels were higher than PM2.5, which he said indicated the movement of dusty and dry air from external regions. PM10 particles are generally larger and can be associated with dust and resuspended soil, while PM2.5 consists of finer particles that can penetrate deeper into the respiratory system. The report does not provide the underlying monitoring-station readings, but the distinction is important because it suggests that Mumbai’s worsening air is not being driven only by combustion sources within the city.
The same explanation also clarifies why local pollution controls cannot be separated from regional weather. Murtugudde said vehicular emissions and industrial pollution were continuously present in the atmosphere. Rain helps wash away some of these pollutants, but El Niño-related suppression of rain can make their removal more difficult. The result is a pollution problem in which the city’s own emissions interact with conditions over a much larger geographical area.
Mahesh Palawat, vice-president of climate change and meteorology at Skymeg Weather Services, described another pathway. Strong El Niño conditions can indirectly increase pollution by reducing widespread rainfall and leaving the surface dry. Loose soil and dust particles can then become suspended in the air and contribute to PM10 pollution. This mechanism is especially relevant for a city undergoing extensive construction and redevelopment, where exposed soil, uncovered material and vehicle movement can add to the background dust load.
The post-monsoon transition therefore changes the operating environment for Mumbai’s construction and transport systems. During the rainy season, wet surfaces can limit the movement of dust. After the rains withdraw, dry road edges, excavation zones, demolition areas and debris routes can become more active sources of resuspended particulate matter. The report specifically identifies major construction and redevelopment sites, infrastructure projects, open waste-burning locations, debris-dumping points and traffic-congested areas as pollution hotspots requiring attention.
The city’s institutional response is being organised through the Brihanmumbai Municipal Corporation. On October 2, the BMC launched fresh standard operating procedures to prepare for pollution. Each civic ward is expected to identify at least 10 pollution hotspots. An officer will be assigned to each hotspot to monitor air quality and ensure corrective measures are taken.
This approach is significant because it shifts part of the response from general citywide warnings to location-based administration. A citywide AQI number can indicate the broad condition of the atmosphere, but it does not identify the construction site, road corridor, waste-burning location or debris point contributing to local exposure. Ward-level hotspot mapping can connect monitoring to specific enforcement responsibilities, provided the designated officers have access to reliable readings and the authority to require corrective action.
The supplied report does not specify the total number of hotspots expected across Mumbai, the enforcement powers of the assigned officers, the frequency of inspections, the penalties for violations or the corrective measures to be imposed. It also does not establish whether the new SOPs include requirements for dust suppression, covering of construction material, washing of vehicle tyres, control of debris transport or action against open burning. Those details will determine whether hotspot identification becomes an administrative register or an operational pollution-control system.
The timing of the BMC measures also exposes a recurring governance challenge. Mumbai has faced winter air-pollution episodes over the past five years, according to the report. Although monitoring stations showed improvement in 2025, unhealthy air is described as becoming a new normal. This suggests that seasonal deterioration is no longer an isolated winter event but a recurring feature that needs preparation before pollution levels rise.
The city’s pollution risk is consequently shaped by two parallel systems. The first is atmospheric: monsoon withdrawal, rainfall deficit, wind circulation, humidity, dust movement and the likelihood of fewer post-monsoon showers. The second is urban and administrative: vehicle emissions, industries, construction, redevelopment, waste burning, debris dumping and traffic congestion. Weather can intensify the consequences of these sources, but it does not eliminate the need to control them directly.
The report also places Mumbai’s air-quality problem within Maharashtra’s wider water and climate stress. A drought declaration covering 265 of 358 talukas indicates that the state is dealing with a broad rainfall deficit. For Mumbai, the immediate implication described by experts is a potentially longer dry period and reduced intermittent relief from post-monsoon showers. The evidence supplied does not quantify how long the dry spell will last or provide a forecast for the city’s winter AQI, so the precise trajectory remains uncertain.
What is established is the sequence already visible in the city: monsoon withdrawal, an AQI increase from the good category to above 100, dust-laden winds, and a civic plan focused on pollution hotspots. What remains to be assessed is how the BMC’s ward-level system performs once dry-weather pollution intensifies. Monitoring will need to show whether the identified hotspots receive timely intervention and whether the city can distinguish regional dust effects from preventable local emissions.
Mumbai’s air-quality challenge is therefore not only a seasonal forecasting problem. It is also a test of whether municipal systems can translate atmospheric information into action at the locations where citizens encounter pollution. The coming post-monsoon period will show whether the new hotspot-based SOPs can address the urban sources that remain within civic control while the city faces a drier and more difficult atmospheric backdrop.