What is Mumbai doing about its growing road dust problem? – Hindustan Times

Mumbai: In January, the National Environmental Engineering Institute (NEERI) submitted a report to the state government, examining the sources of air pollution in Mumbai and their individual contributions to the overall pollution load, which attributed 71% of all PM10 pollution in Mumbai to road dust. NEERI had shared preliminary details last March itself. In August 2021, however, the Maharashtra government decided to allocate 8% of its clean air funds (sanctioned by the 15th Finance Commission in 2020) — ₹99.22 crore of ₹1,240 crore — toward dust mitigation in the city.

The remaining 80% of the clean air funds ( ₹992 crore) has been allotted to electrifying public transportation in Mumbai under the Maharashtra Electric Vehicle Policy 2025, officials privy to the development confirmed. The clean air funds are meant to be utilised by the end of the financial year 2026.

Officials and experts HT spoke to said that a concerted effort is required to mitigate the growing contribution of road dust to the pollution load.

PM10 —aerosolised solid particles less than 10 microns in diameter —are so tiny that they essentially act as a gas and penetrate deep into human lungs when inhaled. Preliminary findings from the NEERI study indicate that a majority of pollutants arising from road construction and heavy traffic on areas of high road surface erosion comprise particulate matter 10 (PM) pollution in Mumbai. The extent and sources of PM2.5 pollution levels are part of the final report, which isn’t available publicly.

Chronic exposure to such suspended particulate matter can trigger a range of health conditions from asthma to high blood pressure, heart attacks and strokes, and increases prevalent morbidity in the population. PM (categorised as PM10, PM2.5 and PM1 depending on their size) are the most prevalent air pollutants by volume compared to other gaseous pollutants like carbon monoxide, nitrogen and sulphur oxides, ozone, among others.

To be sure, some experts have lauded Maharashtra’s decision to utilise the bulk of its clean air funds for its EV Policy. However, others have cautioned that funding for important measures like mechanical road sweeping and air quality monitoring may fall short. NEERI’s findings were part of a source apportionment study for the Maharashtra Pollution Control Board (MPCB).

What is road dust?

Road dust refers to solid particles generated during the handling and processing of road-building and construction materials, such as gravel and concrete. Turbulence generated by traffic, particularly in areas where road surface erosion and tyre wear are high also generates and resuspends fugitive particles.

According to the NEERI findings, 45% of road dust 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.

In fact, 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.

These findings suggest a proportional increase in certain polluting activities, such as road laying and construction and demolition, during the same time. NEERI’s earlier study — which estimated that roads emitted over 7,924 tonnes of particulate matter into Mumbai’s atmosphere each year — had prioritised a 15% reduction in PM emissions from paved roads by the year 2017 and a 100% reduction in emissions from unpaved roads in the same time.

Though NEERI’s latest findings are not available publicly, an analysis by Urban Emissions (revealed 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 over NEERI’s 2010 findings.

How can road dust be managed?

Nearly all experts who spoke to the Hindustan Times said that dust management does not require large budgets but a few simple interventions. Tanushree Ganguly, from the Delhi-based think tank Council on Energy, Environment and Water, commended Maharashtra on its decision to divert majority of clean air funds toward EVs, but said, “Urban local bodies tend to underestimate the contribution of road dust to air pollution, so it would be cautious to pay a little more attention to that.”

According to Dr Rakesh Kumar, former director at NEERI who oversaw the recent study commissioned by MPCB said the key intervention was to build better roads. And a stronger watch on project management consultants and contractors is vital. “Take the Bandra-Worli Sea Link for example. It hardly sustains any damage or has to be revamped. Other roads are not as well built, and when they suffer wear and tear a lot of that material ends up as dust. Mumbai’s poor roads are leading to poor air quality as well.”

Dipankar Saha, former head of the Central Pollution Control Board’s air quality laboratory in Delhi, who has been involved in drawing up dust mitigation plans for Delhi, suggested a range of complementary measures, from using mechanical dust sweeping machines (designed to sweep dust into chambers, or vacuums), use of chemical or enzymatic dust suppressants, conversion of non-paved roadsides into paved surfaces, greening road shoulders, medians and islands to act as dust traps, and to carry out soil stabilisation on unpaved roads.

In civil engineering, this refers to a use of additives (such as salts lignin sulfonate and calcium chloride, or bio-mulches and bio-polymers) to improve the soil’s moisture content and cohesion, and makes it more resistant to erosion.

“Dust is a localised problem,” Saha said, and it needed localised solutions.

“Depending on the area, you can impose speed limits to reduce turbulence from passing vehicles which kick up dust. You can use anti-smog guns to spray atomised water and either chemical or enzymatic dust suppressants where construction work is booming. In Delhi, identification of road dust hotspots is done by municipal corporations and pollution control boards routinely, but the measures are not as effective.”

Mumbai has an advantage: sea breeze. “Even simple mitigation measures should have a more demonstrable impact in Mumbai than most cities in north India,” he said.

What is Mumbai doing?

Dr VM Motghare, joint director (air quality), MPCB, said that authorities were implementing appropriate steps in response to this emerging pollution trend. Mumbai’s city-level action plan to combat air pollution included “preparing plans for creation of green buffers along the traffic corridors and blacktopping of metalled roads,” he said. A total of 364 green traffic islands have also been planned across the city to act as dust traps.

Motghare also said that NEERI has drawn a road map for the MPCB on Dust Management in Urban Regions, suggesting steps in line with expert recommendations cited earlier. A copy of the document has been reviewed by HT, and suggests use of dust suppressants whose effectiveness has been tested under Indian conditions in both laboratory studies and field trials.

An executive engineer in the Brihanmumbai Municipal Corporation’s roads and traffic department added that the municipality too was taking steps to curb the problem of air pollution on poorly built roads, under its Mumbai Street Transformation Programme executed in partnership with World Resources Institute.

The 2022 proposal aims to retrofit all paved and unpaved streets within the BMC’s jurisdiction over a three-year period, under which all design proposals (provided by project management consultants) will first be vetted by a seven-member Technical Review Panel comprising the Chief Engineer (Roads & Traffic, Deputy Chief Engineer (Roads Planning), Zonal Deputy Chief Engineer (Roads), Deputy Commissioner of Police (Traffic), the assistant municipal commissioner from respective wards, a municipal architect, and one member of WRI-India. Concurrently, the BMC will appoint independent Quality Monitoring Agencies (QMA) to oversee the work done by contractors.

“The QMAs will have to scrutinize a Quality Assurance Plan and work methodology that will be submitted by the contractor, and check whether it adheres to the BMC’s own quality manual, along with relevant codes of the Bureau of Indian Standards, and relevant conditions of the tender if any. The same will be recommended or deferred for approval to MCGM,” the executive engineer seeking anonymity said.

Tenders inviting bids from both PMCs and QMAs have been floated by the BMC, and will close in the first week of February.

At present, dust-sweeping machines are the BMC’s only intervention, and cover only about 253 km of the city’s 2,000km wide road network every day. This coverage, officials said, will be widened as the National Clean Air Program (NCAP) is implemented in the city.