As pollution starts tightening its grip around the national capital again, triggering Stage I of the city’s Graded Response Action Plan (GRAP), the only thing more predictable than Delhi’s toxic air is the discourse around it. Every talking head points to the weather, the geography, the cars. What few talk about is where all the agencies have dropped the ball. It’s that four-letter word in the pollution story: dust.

Dust is what accounts for PM 10 and PM 2.5 — the fine, lethal particulate matter that clogs lungs and sneaks into the bloodstream. Dust is what remains in the air, irrespective of weather. And unlike the weather, it is the one villain most easy to fix.

On the ground, however, the reality is different.

The Indian Express investigated one year’s records, March 2025 to March 2026, of daily movement logs of Delhi’s key weapon against dust, the Mechanical Road Sweeping Machine (MRSM). Using geospatial mapping and route-level analysis, a dashboard was created to track 52 geo-tagged MRSMs managed by the Municipal Corporation of Delhi (MCD) — the largest fleet in the capital — across 12 months. The investigation, based on coverage, frequency and concentration of mechanised sweeping across seasons and municipal zones, found that the capital’s clean-up infrastructure barely scrubbed the city’s surface.

Indeed, the investigation found, these machines cover a fraction of the city, with a fleet that is vastly underpowered: just 76 in all, including 52 run by the MCD, during a majority of the period examined by The Indian Express. This is a shortfall of 429 machines from the 505 recommended by the Centre to the Commission for Air Quality Management (CAQM).

The MCD acquired six additional MRSMs last month and eight more subsequently. The other key civic body, New Delhi Municipal Council (NDMC), added five more MRSMs this year to its fleet of four. Yet, the revised count of 95 MRSMs is still over 80 per cent short of what is needed.

The Indian Express investigation also zoomed in on the main sources of dust, prised open systemic gaps and tracked these MRSMs on the ground to find out how the dust is collected by teams of drivers and sanitation workers and the challenges they face.

The findings are telling.

Just five of the 52 designated routes of MRSMs account for nearly 18 per cent of their total running and sweeping distance. And, the clean-up is mainly focused on a small group of routes at a time: one-third of the entire active fleet was concentrated on the busiest MRSM paths — 15 of 52 designated routes — where the machines travelled the most distance. On an average, each route covered 61 km of combined sweeping and running length — in line with the MCD’s operational benchmark. As a result, half of the total operational distance recorded in the city was on these routes, indicating that large parts received little or no coverage. For context, imagine a vacuum cleaner covering only one tiny corner of one room in a house, leaving the rest of the floor caked in dust.

There’s more: the fleet operates below capacity for much of the year, including peak dust months. Deployment is skewed towards winter, when air pollution peaks politically — a reactive rather than preventive posture. Coverage across municipal zones is sharply uneven, with better-funded zones faring considerably better.

The investigation also found gaps in planning, funding and execution that have allowed dust pollution to persist, despite the magnitude of the problem being clear for years. A landmark 2016 source-apportionment study by IIT Kanpur had identified road dust as the single largest contributor to Delhi’s air pollution, accounting for 56 per cent of PM 10 emissions and 38 per cent of PM 2.5.

This echoed findings from this newspaper’s 2015 investigative series, Death By Breath, which documented how previous air quality gains, including the conversion of Delhi’s public transport fleet to CNG and the launch of its Metro, were reversed as officials repeatedly ignored rising dust levels and health hazard warnings.

New records investigated by The Indian Express show how the Centre arrived at its 505-machine figure: 246 small machines for 9,855 km of roads with a right of way (RoW) — road width open for traffic — of under 20 feet; 91 medium machines for 7,277 km of roads between 20 and 60 feet; and, 168 large machines for 13,409 km of major roads with RoW over 60 feet.

The final number was based on how often the roads need to be cleaned, records show. In this case, experts recommended cleaning on alternate days. When calculating how much road each MRSM must cover, the experts considered the length and edges of the surface. The calculation: 1 km of road without a divider (two edges) requires 2 km of cleaning while 1 km of road with a divider (four edges) requires 4 km of cleaning.

Capacity concerns were flagged multiple times. Minutes of high-level official meetings from 2024 show that Delhi needed more than the 85 machines then in operation. In 2025, the Prime Minister’s Office directed agencies to expedite procurement, primarily addressing the MCD and New Delhi Municipal Corporation (NDMC), the capital’s two main civic bodies. At a meeting in April last year involving the PMO, officials noted that at least 1,000 additional machines would be needed across the National Capital Region (NCR) for comprehensive coverage. According to Delhi Environment Department officials, the MCD alone still faces a shortfall of over 100 mechanised sweepers, based on the benchmark of one machine per 40 km of road.

Most sweeps in winter, least in summer

Even during last winter, when stricter pollution-control norms required peak deployment, the MCD did not operate all 52 of its machines available at the time simultaneously.

The gap was more pronounced in summer, when road dust is the single largest contributor to Delhi’s air pollution, accounting for an estimated 38 per cent of PM 2.5 and 41 per cent of PM 10, according to a 2018 TERI study. During those months last year, only 25 sweeping routes were active citywide on a typical day. By December, machines with traceable movement had risen to 43 — expanding coverage, but still short of full utilisation. In a sharp turn, March 2026 saw active routes fall to 15.

This unevenness shows up starkly in distances covered, or median distance covered by all machines in a day. In summer 2025, the fleet covered 1,629.1 km. This dipped to 1,284.15 km during monsoon, climbed to 2,231.7 km in the post-monsoon period, and peaked at 2,591.57 km in December — nearly 60 per cent higher than summer levels. This figure sustained through February, only to drop again by 60 per cent in March (1043.55 km). In other words, the city sweeps hardest in winter, when the political pressure is greatest. In summer, when the dust is worst, it sweeps least.

Uneven coverage across zones

The MCD divides Delhi into 12 zones, each assigned a fixed number of machines. Central and South have the largest fleets (7 each), followed by West and Najafgarh (6 each), Shahdara South (5), Keshavpuram and Rohini (4 each), and Civil Lines, City SP, Karol Bagh, Shahdara North and Narela ranging from 2-3 each — the count excludes the six machines bought this month.

Shahdara South, Rohini and Keshavpuram consistently recorded the highest median daily distances — around 230-260 km across most seasons. Narela, Najafgarh, Shahdara North, Civil Lines and Karol Bagh consistently lagged, averaging only 120-150 km per day even in winter. The gap between high and low-performing zones remained largely unchanged across seasons. West Delhi was the lone exception — median daily coverage rose from just 39 km between June and August to 211 km by December.

The MCD did not officially respond to an emailed questionnaire from The Indian Express on its key findings. However, when asked why a few routes were more active than the rest, a senior MCD official said, “The difference in median daily distances could be because of the network of PWD roads being more in a few zones rather than others. Each zone is a combination of bigger PWD roads and arterial MCD roads. Currently, the MRSMs cover only the PWD roads.”

Asked how MRSM routes are decided, the official said: “They are determined by traffic congestion — like at Ring Road, where there is movement of heavy vehicles such as buses. Beyond the designated fleet, machines are often deployed in response to requests from senior officials for their respective zones. For example, since many VIP residences are located in the Central Zone, a larger share of the fleet is allocated there.”

Limited reach, repeated hotspots

Across this period, coverage of major roads remained just above the halfway mark. In summer, only 51.59 per cent of major roads were covered. Coverage improved in monsoon to about 60 per cent, rising marginally in the post-monsoon period. It stood at 60.5 per cent in November, when stricter pollution response measures were in place, before dropping to 41.24 per cent by March 2026.

Over the one year, the fleet collectively covered a maximum of 2,891 km — about 70.38 per cent of Delhi’s major roads. When all motorable roads are taken into account, only around 23.31 per cent were covered at any point.

Spatial mapping of sweeping activity showed machines repeatedly logging high movement in the same clusters: Wazirpur Industrial Area, Model Town, Seelampur, Dilshad Garden and, from November onwards, Okhla Industrial Area — all locations identified by the Delhi Environment Department as dust pollution hotspots.

Why these machines matter

A 2020 audit by TERI found that MRSMs “are certified as PM10 efficient or capable of picking up greater than or equal to 80% of PM10 particles which is stirred up from vehicular traffic on paved roadways”. The report pointed to Indore, officially one of the country’s cleanest cities, where the use of MRSMs brought respirable suspended particulate matter levels down considerably, from 145 mg/Nm3 to 75-80 mg/Nm3.

The last available official break-up of these MRSMs is from April 2025, according to the Delhi Environment Department: MCD (52), National Highways Authority of India (20), New Delhi Municipal Council (6), Delhi State Industrial and Infrastructure Development Corporation (3), Delhi Cantonment Board (3), National Capital Region Transport Corporation (1), and Central Public Works Department (1).

“The fleets under a few of these agencies have changed since last year. For instance, a total of six MRSMs, each costing Rs 58.69 lakh, were added to the MCD’s fleet last month and eight more have been procured,” the MCD official said.

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