It’s not even Diwali, and a toxic haze has already covered Mumbai. Vaishnavi Chandrashekhar spoke to IIT Bombay environmental scientist Abhishek Chakraborty about what’s behind the early pollution and whether govt’s measures will help.Mumbai saw a spike in air pollution levels last week, with visible haze. What do you think is happening?With a few days or even a week of haze, we can’t be sure. Maybe the wind came from a direction that had a lot of pollution. But one thing that’s been happening pan-India is that wind speeds have been slowing, partly because of climate change. This means mixing of air is getting less efficient, leading to more accumulation of pollution. Some studies indicate a slowdown is also happening in Mumbai’s sea breeze. So its effectiveness in reducing pollution could be declining.Unlike Delhi, Mumbai always had the advantage of coastal winds.There are three components influencing pollution: emission, meteorology, and chemistry. Mumbai has high emissions, but the meteorology used to be in our favour. Chemistry has never been in our favour because Mumbai has good sunlight and humidity, which are both conducive to producing secondary pollutants. It was only meteorology that saved us, and now that is getting weakened. I suspect that untimely haze events are going to increase in the future. Warmer temperatures can also accelerate some of the atmospheric reactions involved in the formation of ground-level ozone and secondary particulates.How do sunlight and humidity influence pollution?Sunlight produces radicals that oxidise primary emissions. For instance, sulphur dioxide and nitrogen oxides can undergo chemical reactions that produce nitrates and sulphates. These form secondary particulates, including harmful PM 2.5. In photochemically active regions, especially in the tropical belt, you may get more formation of secondary particulates. Humidity can also influence these reactions.Emissions have increased, too. Vehicle numbers are up and construction activity has surged.Emissions have increased, of course, and construction is part of that. Construction activity contributes a lot of coarse particles, which can increase pollution load and reduce visibility. These particles can also contribute to secondary particulate formation.But I’m not sure construction activity has shifted the regime. The regime shift is happening because of longer-term changes in climate, temperature and humidity. Mumbai may be losing its natural advantage, which makes us feel the pinch of increasing emissions even more.Last week, we saw official air monitors record lower pollution levels compared with independent platforms like IQAIR.Regulatory bodies like CPCB and MPCB use instruments that are the gold standard for air quality measurement, compared with the low-cost sensors and satellite data that these groups use. But there are many factors that affect the results of reference-grade monitors: Are they being calibrated properly? Are they relaying data correctly?The BMC announced misting and other spot measures. What do you make of these?As a scientist, I’m really tired of seeing measures announced without any data on whether they work. Misting, for example, will increase local moisture levels, which could be counterproductive. No effectiveness studies have been conducted, or if they have, they are not in the public domain.It also takes enormous manpower and resources to carry out misting on all the roads. A tenth of those resources could be spent first testing if it will work. You can use simulations to test different scenarios, which can then be tried out in one or two locales. If they work, then try mass deployment. Not mass deployment first. But simulations require a good emission inventory. Establishing an emission inventory, and then updating it every year or every two years, should be the first step for any city.But we do need some emergency measures.Short-term actions can work if they are backed by science and focus on a hotspot. The authorities can leverage technology—drones and AI, for instance—to find and track hotspots and then curb the source.The solution is ultimately long-term. There must be a continuous effort. You cannot just take haphazard action when pollution season comes along. We also have to ask whether, as a society, we are doing everything we can—such as taking public transport and reducing car use. Curbing vehicle emissions can help reduce occurrences of haze because vehicle exhaust contains nitrogen oxides that contribute to haze formation. But we put convenience ahead of the environment.
