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Delhi’s polluted air, the diagnosis and the prescription

Along with vehicles, construction and industries, the study has identified road dust, coal-based tandoors and concrete batching as major sources of air pollution in Delhi.

Written by Apurva | New Delhi |
Updated: January 14, 2016 7:59:09 am
Wednesday evening, Delhi. Study says contributors to winter haze are secondary particles, combustion emission. Tashi Tobgyal Wednesday evening, Delhi. Study says contributors to winter haze are secondary particles, combustion emission. Tashi Tobgyal

A study by IIT Kanpur assesses various aspects of air pollution in Delhi and recommends measures to improve air quality. APURVA looks at the findings

Sources: Road dust is culprit No 1, vehicles No 2 for PM2.5

The Delhi government’s odd-even road rationing policy will possibly resume with the government proposing to evaluate the effects between January 1 and January 15. Beyond odd-even, an IIT Kanpur report on air pollution in Delhi has made a slew of recommendations required till 2023 after identifying the top sources of emission.

Along with vehicles, construction and industries, the study has identified road dust, coal-based tandoors and concrete batching as major sources of air pollution in Delhi. The study has estimated the total PM10 emission load in the city at 143 tonnes per day and listed the top contributor as road dust (56%) and the PM2.5 load at 59 t/d, the top contributors being road dust (38 %) and vehicles (20 %), followed by domestic fuel burning and industrial point sources.

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These are the second largest source of particulate matter, particularly PM2.5. According to the report, vehicular pollution grew from 64 per cent to 72 per cent between 1990 and 2000. In winter, on average vehicles can contribute 25 per cent to PM2.5 and at certain locations this could be above 35 per cent. There is a significant contribution of diesel vehicles to PM10 and PM2.5.

Road dust

The silt load on some of Delhi’s roads is very high and silt can become airborne with the movement of vehicles. The estimated PM10 emission from road dust is over 65 tonnes per day. Soil from open fields too gets airborne in summer. In some parts of the city, roads are broken, poorly maintained and partially paved surfaces and the study found that movement of vehicles may cause non-exhaust road dust emission in significant amounts. PM10 and PM2.5 emission from road dust is 79,626 kg/day and 22,165 kg/day respectively.

Concrete batching

During the study period massive construction activities were found that required concrete batching, including at 60 DMRC locations where construction was under progress. It was assumed that there will be 40 concrete batching plants of 120 cu.m/hr capacities operating for 16 hours. Several medium and small construction activities were also observed in the city. PM10 and PM2.5 emissions from concrete mix plants is estimated at 14.37 tonnes/day and 3.5 tonnes/day respectively. A few hundred plants in NCR may contribute to this.

Hotels and restaurants

Details of hotels and restaurants were obtained from DPCC, and related websites. The field survey found that hotels, restaurants, etc use coal as fuel in tandoors. The average consumption of coal in tandoors based on the survey was 30 kg/day. The number of hotels and restaurants was 36,099 (Delhi Statistical Handbook, 2014). The study assumes 25% of these enterprises use tandoors for food preparation.

Municipal solid waste burning

The contribution of burning MSW may surprise many. A study in 2015 in Delhi has estimated 190 to 246 tonnes/day of MSW burning. It is a myth that MSW is not burned in Delhi, the IIT study says. This emission, it says, is expected to be large in the regions of economically lower strata of the society, which do not have the infrastructure for collection and disposal of MSW.

Diesel generator sets

Diesel generator sets are used as the source of power in shopping complexes and industries during the power-cut hours. The IIT Kanpur survey concluded that there is minimum of 2 hours/day power cuts in the city, especially in summer.


The pollutants: Potassium to PM2.5, the killers


The study found potassium levels high and variable; 18 to 7 migrograms per cubic metre in PM10 and 15 to 4 µg/cu.m in PM2.5. The level should ideally be less than 2µg/cu.m. The levels indicate burning of a large biomass, and in variable amounts. The highest levels were in early winter. The study says this was perhaps due to massive crop residue burning in Punjab and Haryana.

PM 10

In PM10, the crustal component (silicon + aluminum + iron + calcium ) accounts for about 40 per cent in summer and 13 per cent for winter. This suggests soil and road dust and airborne fly-ash are the major sources in summer. Secondary particles (nitrates+sulphates+ammonium) account for 13 per cent of PM10 in summer and 26 per cent in winter; combustion-related total carbon accounts for 7 per cent and 19 per cent.

PM 2.5

The crustal component was found accounting for 20 per cent of PM2.5, which reduces to only 3.5 per cent in winter. This suggests soil and road dust and airborne fly-ash is a significant source in summer. The secondary particles account for about 17 per cent in summer (28 per cent in winter) and combustion-related total carbon accounts for 9 per cent (23 per cent in winter).

The recommendations: In to-do list, how to reduce vehicular emission by half

What the study recommends for various pollution sources, and how much reduction it estimates in pollution from each source.

Road dust

Mechanical sweeping with water wash: If main roads are swept twice a month, road dust emission will be reduced by 23 per cent; if four times a month, it will be down by 52 per cent, the report says.
Effect: 71 µg/cu.m reduction in PM10 likely.
Vacuum-assisted sweeping: The report recommends sweeping four times a month.
Effect: 93 µg/cu.m reduction likely in PM10 as a result of a 71% reduction in road dust emission


Diesel particulate filter: PM emission reduction efficiency of 60-90 per cent.
Effect: 10 µg/cu.m improvement in PM concentration.
Electric/hybrid vehicles: If introduced, then by January 2017, study assumes, 2% two-wheelers, 10% three-wheelers and 2% four-wheelers will be electric/hybrid.
Effect: 4.5% reduction in PM emission, 1-2 µg/cu.m net improvement in air quality.
Sulphur: Bring down sulphur content to 10 parts per million (ppm) by end-2017.
Effect: 6% drop in PM10 and PM2.5 emission from vehicles.
51% overall reduction in vehicular emission if all recommendations implemented.


Recommendation: Study suggests that industries be made to use light diesel oil and high speed diesel with sulphur content 500 ppm or less in boilers or furnaces. Allow no new polluting industry, it adds.
Effect: 15 to 30% control in PM from this source, negligible sulphur-dioxide.

Diesel generators

Recommendation: Reduced sulphur content to 500 ppm.
Effect: 15 to 30% reduction in PM emission from this source from present 1400 kg/d.

Cooking fuel

Recommendation: Ban coal for cooking, shift to electric or gas-based devices, stop burning municipal solid waste. Every day, these sources contribute an estimated 12.8 tonnes/day of PM 10
Effect: 57% reduction in PM 10 from these sources.

Concrete batching

Recommendation: Spray water at construction sites, use wind breakers, bag filters at silos, cover sites.
Effect: 49% reduction in PM10 and PM2.5.

The neighbourhood: NCR air equally bad, call to involve it too

The study highlights the importance of involving the National Capital Region (NCR) cities in controlling air pollution. “The levels in Delhi and NCR are similar and comparable; it suggests that air pollution levels could be contiguously high in the NCR… In other words almost about one-third of pollution PM levels can be attributed to emissions from outside Delhi. This analysis makes it clear that pollution control will have to focus both inside and outside Delhi for improvements in air quality not only in Delhi but the entire NCR.”

According to the report, sources outside Delhi (excluding secondary particles) contribute about 100 µg/cu.m of PM10 and 59 µg/cu.m of PM2.5 in Delhi.

“As a next step towards attaining air quality standards, since the NCR is a contiguous area with similarities in emitting sources, it is proposed that the control options are implemented for the entire NCR. With the implementation of control options in Delhi as well as NCR, the overall air quality in Delhi will improve significantly and expected mean PM10 levels will be 120 µg/cu.m and PM2.5 will be 72 µg/cu.m. In addition to the above control options, some local efforts will be required to ensure that city of Delhi and NCR attain the air quality standards all through the year and possibly for many years to come,” states the report.

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