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Mumbai ranks as India’s most polluted city and fifth globally in the latest iQAir assessment, with an AQI of 152. (Img: X)
Mumbai: This business capital of the country has emerged as India’s most polluted city and the fifth most polluted globally in the latest iQAir rankings, with an Air Quality Index (AQI) of 152, classified as unhealthy. The deterioration has drawn attention to a combination of ground-level ozone, construction-related dust, vehicular emissions and weather conditions that are preventing pollutants from dispersing.
The findings present a troubling picture for a coastal metropolis traditionally considered better placed to disperse pollution because of its sea breeze. Unusually high temperatures and weaker winds have undermined this natural advantage, allowing pollutants to accumulate closer to the ground.
According to the iQAir assessment reported by The Indian Express, ground-level ozone was the principal pollutant behind the city’s elevated reading. Ozone forms when nitrogen oxides and volatile organic compounds react in the presence of sunlight. Hot weather can accelerate these chemical reactions, contributing to higher concentrations of the pollutant.
However, the assessment differs from the picture emerging from India's official monitoring system. Data from the Central Pollution Control Board (CPCB) placed Mumbai's overall AQI at 98, within the satisfactory category. Several neighbourhoods, including Deonar and Bandra Kurla Complex (BKC), nevertheless recorded elevated pollution levels.
The difference between the two assessments underscores how pollution readings can vary according to monitoring networks, measurement methods and the locations being assessed.
Ground-level ozone is a secondary pollutant, meaning it is not emitted directly from a single source. Instead, it develops through chemical reactions involving nitrogen oxides and volatile organic compounds, which can originate from vehicles, industrial activity and other combustion-related sources.
Strong sunlight and high temperatures can intensify ozone formation. Mumbai's unusually hot conditions this October have therefore raised concerns about the accumulation of the pollutant, particularly as the city's normal air circulation patterns have weakened.
Atmospheric scientist Gufran Beig has attributed the deterioration in Mumbai's air quality to an El Niño-related weather pattern, which has been associated with higher temperatures and reduced wind speeds. Poorer ventilation allows pollutants to remain concentrated in the lower atmosphere rather than being dispersed.
The city's coastal location ordinarily helps clear airborne pollutants through changing wind patterns. When these winds weaken or their usual reversal is delayed, however, emissions from local sources can remain trapped over populated areas.
While weather conditions influence how pollution accumulates, human activities remain a major source of emissions. Construction projects, road dust, vehicular exhaust and the burning of waste are among the factors contributing to poor air quality across Mumbai.
CPCB monitoring data identified particulate matter, particularly PM2.5 and PM10, as major pollutants in affected areas such as Deonar and BKC. PM10 includes coarser particles such as dust, while PM2.5 consists of much finer particles capable of penetrating deep into the lungs.
Deonar has faced particular concerns over waste burning, including the burning of plastic and garbage, which releases pollutants into the surrounding air. Construction and road dust can further increase particulate concentrations, particularly when dry conditions and weak winds limit dispersion.
The combination of local emissions and unfavourable meteorological conditions can cause pollution levels to rise sharply in individual neighbourhoods even when the city's overall AQI remains comparatively lower.
The Brihanmumbai Municipal Corporation (BMC) has initiated measures to identify and address local pollution hotspots. Officials have been assigned across 26 municipal wards to monitor problem areas and undertake measures to control emissions.
The initiative comes amid growing concern over the recurrence of poor air quality in Mumbai during the post-monsoon period. The withdrawal of monsoon rainfall reduces the regular washing out of airborne particles, while dry weather can increase the amount of dust lifted from roads and construction sites.
Pollution-control measures at the local level are therefore expected to focus on identifying emission sources, enforcing dust-control requirements and addressing activities such as open waste burning.
However, the contrasting readings reported by different monitoring systems also highlight the importance of reliable, consistent air-quality data. Accurate measurements are essential for identifying pollution hotspots, assessing the severity of exposure and determining whether mitigation measures are working.
Ground-level ozone and particulate matter pose different but significant risks to human health. Ozone can irritate the respiratory system, aggravate asthma and reduce lung function. Fine particulate matter can penetrate deep into the respiratory tract and is associated with respiratory and cardiovascular illnesses.
Children, older people, outdoor workers and individuals with existing heart or lung conditions are particularly vulnerable to polluted air.
The latest readings also challenge the assumption that Mumbai's coastal geography alone can protect it from severe pollution. Although sea breezes can help disperse emissions, their effectiveness depends on prevailing weather conditions and the volume of pollutants entering the atmosphere.
Addressing the problem requires both immediate enforcement and longer-term action to reduce emissions from vehicles, construction, waste burning and other sources. Improved monitoring, effective dust suppression and stricter controls on open burning will be important to prevent localised pollution from escalating.
Mumbai's latest pollution episode illustrates how emissions and weather can combine to create hazardous conditions. While meteorological factors influence the accumulation of pollutants, sustained improvement will depend on reducing the pollution generated within the city and its surrounding regions.
