Road dust main contributor to PM pollution in Mumbai: Study
The contribution of road dust to the city’s overall pollution load has more than doubled over the past decade, reveals the interim results from a source apportionment study conducted by the National Environmental Engineering Research Institute (NEERI).
Select details from this study, which has not yet been finalised, were shared by Maharashtra Pollution Control Board (MPCB) officials during an air pollution townhall organised by the state environment department on Tuesday.
Road dust largely refers to solid particles generated during the handling and processing of road-building materials, such as gravel and concrete. Turbulence generated by passing traffic, particularly in areas with high traffic volume, or where road surface erosion and tyre wear are high, also generates and resuspends fugitive particles which become airborne. Preliminary findings from NEERI’s study indicate that such pollutants make up 71% of all particulate matter pollution in Mumbai.
Of this, 45% comes from unpaved roads (which are more prone to erosion by wind) followed by paved surfaces, which contribute to 26% of the city’s dust load. Another 8% comes from particulate matter emissions traced to construction activities, and 3% to vehicles. The rest comes from industries, the domestic sector, aircraft, marine vessels, open eateries, bakeries, and crematoria.
This marks a significant upswing in the presence of road dust over the last 10 years. An earlier source apportionment study released in 2010, (also by NEERI) had found that road dust makes up only 31% of Mumbai’s particulate matter concentration - with paved and unpaved roads contributing 12% and 18% respectively. This suggests a proportional increase in certain polluting activities, such as road laying, during the same time frame.
NEERI’s earlier study had found, at the time, that paved and unpaved roads emitted over 7,924 tonnes of particulate matter into Mumbai’s atmosphere each year. The study had prioritised a 15% reduction in PM emissions from paved roads by the year 2017 and a 100 % reduction in emissions from unpaved roads by the same time.
A subsequent analysis by Urban Emissions (an air pollution research and advocacy group) suggested that in 2018, “dust emissions from road re-suspension and construction activities” in Mumbai resulted in 7,050 tonnes of PM2.5 and 43,550 tonnes of PM10 emissions - a substantial increase.
MPCB officials said they are taking steps to address these findings. “Road dust was earlier just a third of the total pollution load. This increase needs to be investigated. I have already written a letter to NEERI asking them to conduct a detailed audit for identifying areas where road dust resuspension is a problem. They will start by surveying about 20 locations,” said Dr Sudhir Shrivastava, chairman, MPCB, who did not specify these locations by name.
Officials, including Dr VM Motghare, joint director (air quality), MPCB, and Dr Rakesh Kumar, director, NEERI, confirmed that these preliminary findings have been communicated to the Central Pollution Control Board by NEERI, but did not specify when. “The audit itself will start any day now. A list of areas is being prepared,” said Kumar, who also did not specify the areas by name.
During his presentation as part of Tuesday’s webinar, Dr Motghare revealed that Mumbai’s air pollution action plan (for which funds were recently disbursed by the Centre), includes preparing a plan “for creation of green buffers along the traffic corridors” and “blacktopping of metaled roads including pavements of roads shoulders”, among others. A total of 364 green “traffic islands”, which will act as dust traps, have also been planned. Mechanical sweeping machines, meanwhile, are currently cleaning 253 kilometres of the city’s 2,000km wide road network every day.
On the other hand, NEERI’s preliminary findings also show that emissions from certain sources have also decreased over the last decade. For example, bakeries in the city were found to contribute 3.5% of all particulate matter concentration last year (as opposed to nearly 6% in 2010. Similarly, emissions from landfill fires reduced from 11% to 3.7%.