Amid the rapid road construction that has accompanied the capital’s growth, these roads have contributed hugely to the dust accumulation. According to source apportionment studies of pollutants conducted since the Commonwealth Games, this dust has constituted the majority of particulate matter up to size 10 microns.
Most of the roads in Delhi, which has the country’s highest road density at 2,103 km per 100 sq km, are surfaced, but the unpaved shoulders of paved roads too contribute hugely to dust.
A study by the research organisation SAFAR under the Ministry of Earth Sciences during the 2010 Games, published in the journal Atmospheric Environment, made the following “surprising” conclusion: “The unattended source of windblown dust from paved and unpaved roads is surprisingly found to be the major contributor in PM10 emission.”
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Windblown dust, with roads a major contributor, accounted for 131 gigagrams PM10 per year, more than half the total PM10 generation of 236 gigagrams per year. One gigagram is 1,000 tonnes. A 2014 study by SAFAR placed road dust’s contribution at 52 per cent of PM10.
“In our first study in 2010, we found the majority of PM10 came from road dust. This was in contradiction to previous published studies which blamed vehicular pollution as the major source,” said Dr Gufran Beig, project director of SAFAR.
The study notes that the contribution of windblown dust was more than the total estimation from all other sources — vehicles, industries and cooking fuel — and more than fourfold in comparison to transport emission, which was the second highest contributing source. This was despite 2010 having seen the wettest monsoon in Delhi since 1978.
Experts say road dust throws up heavier PM10 particles rather than the finer PM2.5. “Even though the PM10 particles are larger than PM2.5 and should settle down in a few minutes, in rush traffic hours they cannot settle, and layer after layer of dust is constantly added,” Dr Beig said.
According to statistics with the Ministry of Road Transport and Highways in 2011, 20,903 km of Delhi’s total road length of 29,648 km was surfaced. Of this, 480 km maintained by PWD was surfaced with the highest quality material, either black tops (BT) held together with bitumen, or cement concrete consolidated to a certain thickness.
According to Dr Shashank Bishnoi, assistant professor in civil engineering with IIT Delhi, “The idea is that roads surfaced with these materials throw up the least amount of loose soil and dust compared to unpaved roads and lanes, where soil and dust that is produced is constantly scattered.”
But Dr Beig said, “In Delhi, the side of the paved road next to footpaths is unpaved. These areas, known as shoulders of the road, are where traffic jams happen.”
In the 2010 survey, SAFAR estimated that 10 per cent of the roads in in NCR and Delhi are unpaved. SAFAR recommended that the unpaved roads be paved immediately.
According to Dr B Sengupta, chairman of the core committee that had created a construction manual for the Ministry of Environment and Forest in 2010, “We had said then that paving is the most permanent solution to dust control, suitable for longer duration projects, but its high costs were seen as the prohibitive factors. The other solution was to ensure reducing the speed of a vehicle to 20 kph to give dust time to settle down. For this, speed bumps are commonly used.”