As I moved into the city of Mumbai, I started exploring the neighbourhood of my new workplace. I was delighted by the pleasant weather, as it was the second week of October, just as the monsoon had begun to retreat. Slowly, as the humidity in the air subsided and the weather transitioned towards a drier season, a blanket of haze appeared. While the city of Mumbai is known for its evolving and iconic skyline, this crisp outline seemed to dissolve in the hazy blanket, which made me wonder about the reasons behind this.
While trying to understand the causes, I learned that the haze can be attributed to weather patterns, local activities, and most significantly, air pollution.
Urban haze is formed due to specific scientific processes, including:
Smog formation – Smog is a kind of air pollution that happens when sunlight reacts with pollutants emitted from vehicles and industries. This reaction creates harmful gases like ozone near the ground, making the air hazy and unhealthy to breathe. Smog is experienced in heavily polluted cities like Delhi, Mumbai, Los Angeles, and Beijing, where the air feels thick and hazy.
Temperature inversion – Normally, the hot air at the ground surface rises up and dissipates into the cooler air above. But, when there is an inversion in temperature due to a sudden increase in pollution, a layer of warm air sits above cooler air near the ground. This traps pollutants close to the surface and leads to persistent haze/smog. This is common in cities like Mumbai, especially during the winter and post-monsoon months.
High particulate matter concentration – Particulate Matter (PM) refers to tiny solid or liquid particles suspended in the air. These particles vary in size and composition and come from various sources like vehicle emissions, industrial processes, and construction dust among others.
Although the above are key reasons behind haze formation, low wind speeds, atmospheric stability, and secondary pollutant formation can also be other contributors. In the context of Mumbai, among the above processes, multiple studies show that high Particulate Matter concentration is the primary contributor to haze formation.
We don’t always see air pollution, but in urban areas, it’s inevitably present— shaping the quality of the air we breathe. Some days, the sky looks hazy, the air feels heavy, or there’s a faint smell—small signs that pollution is present.
The U-CAN fellowship’s transformative program is allowing me to delve deeper into these interconnected themes. Through projects related to mitigating and managing air pollution at my host organisation, Artha Global (a policy consulting think-tank), we explore the causes, sources, pollutant contributors and identify strategies to reduce air pollution at different scales.
