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Mumbai Grapples with Worsening Air Quality Due to Climate Change

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While Delhi often grabs headlines for its high pollution levels, it’s essential to recognize that air quality issues extend beyond the national capital. In a concerning trend, Mumbai has been facing deteriorating air quality during the post-monsoon period for the second consecutive year. Throughout most of October, the Air Quality Index (AQI) in Maharashtra’s capital has consistently been in the “moderate” or “poor” range. Notably, the city has yet to experience a single “good” air quality day this month.


In the initial days of October, pollution levels in Mumbai were perceptibly higher than indicated by the AQI. A haze enveloped significant parts of the city, leading to reduced visibility. However, there is a silver lining amidst this challenge: the predominant pollutants are coarser particles that may cause irritation but are generally less harmful than finer particles like PM2.5. While meteorological conditions influence pollution levels, it is essential to understand that weather or climate alone does not generate air pollution. Rather, air quality primarily deteriorates due to anthropogenic sources of emissions, whether local or distant. Meteorological conditions merely affect the dispersion and movement of these pollutants in the air.


Mumbai’s geographic location offers a unique advantage. The coastal city benefits from natural cleaning mechanisms. Strong surface winds facilitate the rapid dispersal of pollutants, and the robust sea breeze effectively sweeps these particles away from the land. This wind reversal pattern is a characteristic feature of Mumbai throughout much of the year. However, the post-monsoon season has raised concerns due to unfavorable meteorological conditions. The city faces greater challenges when the monsoon’s withdrawal is delayed. In recent years, Mumbai has witnessed prolonged periods of poor air quality, defying our conventional understanding of a “normal” environment.


So, why is Mumbai experiencing deteriorating air quality recently? The answer lies in the transformation of the “usual” into the “unusual,” triggered by additional anthropogenic factors. Last winter, Mumbai faced record-breaking particulate pollution, primarily linked to unusual triple-dip La Niña conditions, which are associated with climate change. An abnormal drop in Pacific Ocean temperatures had a significant impact on coastal wind speeds around Mumbai. The regular wind reversals from the Arabian Sea, which disperse pollutants, were notably absent. Consequently, emissions from various anthropogenic sources remained in the atmosphere, resulting in the city’s worst air quality of the decade.


This year, La Niña has dissipated. However, the delayed withdrawal of the monsoon in October has had a significant impact on Mumbai’s air quality. The timing of the monsoon withdrawal is pivotal in determining air quality. Post-monsoon withdrawal leads to the establishment of an anticyclonic circulation directly above Mumbai and its surroundings. This reduces ventilation in the city.


Simultaneously, transport-level winds, higher in the atmosphere, were blowing toward Mumbai from the Sahyadri ranges, around 2,040 feet above sea level. These winds, while moderately fast, carried pollutants toward Mumbai from regions like Lonavala and Khandala. When these winds lost energy, they descended near Navi Mumbai and the coastal areas. Here, they mixed with warmer winds laden with local dust, leading to a decline in air quality. The fact that PM10 remains a major pollutant in the city, impacting visibility, suggests that the primary culprit for the worsening air quality is coarser particles, primarily from dust emissions.


Mumbai is witnessing ongoing construction and development activities, including the coastal corridor, metro projects, and excavation work. Unfavorable weather conditions exacerbate emissions from these sources, contributing to pollution. While under normal conditions, windblown dust constitutes 26% of PM10 and 19% of PM2.5, the surge in pollution indicates that PM10 levels have risen significantly. Additionally, the stagnant conditions likely altered the composition of pollutants.


On some days this month, Mumbai’s AQI exceeded that of Delhi. However, this is coincidental, as Delhi experienced rain that cleared the atmosphere, while Mumbai faced increased particle intensity due to poor ventilation. In the long term, Mumbai’s air quality remains better than Delhi’s, at least up to this point.


Addressing the challenge of air pollution may be a long and complex journey, but it begins with understanding and acknowledging the problem. We must rely on data from reliable scientific sources, rather than denying the issue. Implementing measures such as greening construction sites, dampening dust through regular water spraying, transitioning to fossil fuel-less transportation, and maintaining smooth traffic flow can help mitigate pollution in the short term. Medium-term solutions include the adoption of electric vehicles, efficient solid waste management, cleaning up dumping grounds, and better industrial toxin management. Given the urgency of climate change, taking action on these fronts is crucial.

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