When it comes to curbing pollution in Indian cities, the conversation nearly always centres around vehicular pollution, with states like Maharashtra considering Delhi's odd and even formula for cars on the road. But a detailed analysis of pollution in Mumbai in 2010 shows that vehicular pollution accounts for less than 6% of particulate matter (PM10) in the city. Interestingly, bakeries release a greater proportion of particulate matter in Mumbai than vehicles.
The Air Quality Assessment, Emissions Inventory & Source Apportionment Studies for Mumbai, carried out by the Central Pollution Control Board and National Environmental Engineering Research Institute (NEERI), show that the highest percentage of PM (20%) comes from power plants. But if particulate matter from paved road dust and unpaved road dust are taken together, it pips power plants (over 29%) as the largest source of particulate matter.
But merely studying the quantity of particulate matter released in the atmosphere by various sources paints an incomplete picture of pollution in Mumbai. For instance, while power plants may emit amongst the largest portions of particulate matter, much of it is released at a great height and never actually hits the city, unlike road dust and vehicular pollution, points out Rakesh Kumar, director of NEERI's Mumbai operations and a project leader for the report. Also, much of the pollution caused by vehicles is contributed by heavy vehicles which run on diesel.
Kumar also points to another aspect of air pollution that the report studied - chemical mass balance -which looks at an individual's exposure to pollution at the ground level. For instance, while bakeries contribute 5.8% to the overall levels of PM in Mumbai and crematoria contribute 1.12%, this would be a lot higher for someone living near a bakery or crematorium.
Kumar points to the need for multiple approaches to tackle pollution instead of solely focusing on cars, the way the Delhi government has. The odd and even car rule has failed in other countries where it has been attempted, as there are enough people who will bribe their way past the rule, he adds. Also, he says vehicular pollution contributes under 10% of PM in cities like Delhi, so an attempt at curbing pollution will fail if one only looks at cars.
"In Mumbai, construction, road re-suspension and garbage burning are amongst the highest sources of PM," says Kumar.
The study shows that diesel cars contribute around 20% of PM released from vehicles in the city. Diesel cars contribute 1.17% to Mumbai's overall PM compared with a mere 0.06% for petrol cars. "But if you suddenly decide to replace all diesel cars with CNG, the overall reduction in pollution levels will be minuscule. CNG releases very fine particles into the environment which are also harmful, and are at a much higher temperature than diesel car emissions," says Kumar.
While heavy vehicles account for the lion's share of PM released from vehicular sources, Kumar says one cannot do without them, as the city's economy depends on them. Most of them carry essential supplies. "They are actually amongst the cleanest vehicles. But when overloaded, the pressure on engine results in higher levels of emissions."
