Unusual Weather Patterns Have Made Mumbai's Air Pollution Worse

Air quality in Mumbai remains poor as multiple large projects in the city and its surrounding areas have become dust hot spots.

For the past couple of years, India’s financial capital has been finding mention alongside the Delhi National Capital Region because of winter pollution. Hazy sikes and higher than normal AQI levels have increased cases of cold, cough and other respiratory problems.

That has prompted the civic authorities to ask developers to take dust-control measures and face fines. That comes ahead of Diwali, when, every year, firecrackers add to air pollution.

BQ Prime reached out to Gufran Beig, the Sir Ashutosh Mukherjee Chair Professor at the National Institute of Advanced Studies, IISc campus, and the founder project director of India’s first indigenously developed System of Air Quality and Weather Forecasting and Research, or SAFAR. 

Professor Beig shared his views on key questions regarding the air pollution.

Mumbai has a significant natural advantage due to its geography and coastal line in favour of keeping air quality in check. All coastal regions have relatively faster surface wind speeds during the winter as compared to plains. Surrounded by the ocean from three sides, the city also sees a wind reversal frequently, where cleaner winds originating from the ocean sweep away pollutants and dump them on the other side of the sea.

However, since 2022, disturbed large-scale weather systems, coupled with newly emerging, though temporary, emission hot spots, have deteriorated Mumbai’s air quality. The city was ranked among the worst polluted parts of the country with the onset of winter.

Emissions from anthropogenic (human activity) as well as some natural sources generate air pollution. Weather and climatic factors significantly influence and manoeuvre the distribution of air pollution. A standard physics and chemistry concept conveys how the location of a city and its weather affect pollutants dynamically. Like rain washes away particulate pollutants but not gaseous pollutants; winds sweep away pollutants; calm winds tend to oppose the faster dispersion; and so on.

In the winter of 2022, we encountered an unusual triple-dip La Nina—the cooling of surface temperatures in Pacific waters—of the century. This La Nina, in its withdrawal phase, altered the large-scale wind circulation, which resulted in two changes:

• Slowing down the surface wind speed in most parts of western India, preventing proper ventilation of pollutants.

• Reducing the frequency of cleaner winds originating from the ocean towards land to sweep away the pollutants.

Once the surface winds are slow, they allow the accumulation of particulate pollutants originating from emissions from various sources, including additional dust hot spots originating from redevelopment activities. That additional load, which is over and above normal emissions, tends to increase the pollution level in Mumbai.

In 2023, monsoon withdrawal got delayed in the Mumbai region until October. As we know, monsoon retreat is always accompanied by anticyclonic circulation, which slows down the surface wind speed beneath. As a result, pollution got trapped. When cooler winds blowing from Syadri Hills towards Mumbai met with warmer winds from the plane, the dust got arrested like a vortex, which was then pushed into the city, where it found stagnation. This was the major reason for the increased pollution levels in the second and third weeks of October.

The additional dust lifting in many parts of Mumbai also reduced visibility as it consisted of both finer and coarser particles. This increased hospital visits for people suffering from respiratory ailments.

Once the metro and coastal corridor work is over and we control the redevelopment activities, we expect that peak pollution levels will be reduced. However, unusual weather patterns and subsequent impacts are believed to be a result of climate change. We can’t be sure whether each winter will be the same because climate change itself is all about sudden and unusual surprises that may enhance the impact of local sources of emissions. There is no doubt that alarms are ringing.

Long-term consequences are serious. We are all witnessing what is happening in Delhi each winter. Although Delhi is landlocked while Mumbai is not due to coastal lines, we should also not forget that, being a coastal city, it is also highly vulnerable to global warming and extreme events. Another reality is that the toxicity of the chemical composition of particulate matter is higher in Mumbai than in many metro cities. Once a carrying capacity is crossed, it would be difficult to come back, and, hence, Mumbai should be sensitive to such alarms. 

The key to success lies in strengthening implementation on the ground. Rules and regulations do exist but largely remain on paper. Mumbai should have its own GRAP (graded response action plan). Let’s quickly get rid of all diesel-driven vehicles and transform them into CNG to electric vehicles. Agencies should involve citizens in planning and controlling mitigation efforts. The mitigation strategies should be based on scientific work rather than convenience.

The emission inventory is all about accounting for sources of emissions in a given city. The precise and accurate emission inventory development guides us in choosing priority sources for mitigation. Creating awareness and outreach activities will greatly help in self-mitigation.  

Each city is different and hence needs different solutions. India has unique challenges, distinct emission sources, various airsheds, and different climatology. The country needs a different strategy for tackling them. India’s science base is strong and capable of formulating mitigation strategies. There are quite a few examples of cities like Mexico City, Montana, Beijing, etc. where a systematic approach led to improvement in air quality. However, there is no shortcut. We need long-term planning. To do this we should understand the dynamics of the city and all other related information.    

Scientists should explain and interpret the data in simple terminology for the benefit of citizens and executives. Let us embrace the change and learn from it to find a solution collectively. 

Gufran Beig is Sir Ashutosh Mukherjee Chair Professor at the National Institute of Advanced Studies, IISc campus. He is also the founder project director of India’s first indigenously developed System of Air Quality and Weather Forecasting and Research or SAFAR. 

The views expressed here are those of the author and do not necessarily represent the views of BQ Prime or its editorial team.