Vehicle exhaust, dust, what fouls the air the most? Studies disagree

As Delhi experiments with the ‘odd-even’ formula, Indian Express summarises the findings of a range of source apportionment studies on air pollution in the Capital over the last several years.

Written by Pritha Chatterjee | Published: January 6, 2016 2:35 am
A foggy polluted evening at the Vijaypath facing the Rashtrapati Bhavan in New Delhi on monday. Express Photo by Tashi Tobgyal New Delhi 071215 A foggy polluted evening at the Vijaypath facing the Rashtrapati Bhavan in New Delhi. (Express Photo by: Tashi Tobgyal)

Critics of the Delhi government’s ongoing odd-even road rationing policy have complained that it targets private cars, a relatively small polluter, ahead of addressing bigger concerns like emissions from heavy vehicles and two-wheelers, road and construction dust, and polluting industries.

Over the years, source apportionment studies by multiple research institutions have differed on the relative contribution of traditional and emerging sources to particulate matter in Delhi’s air. Assessments of the share of vehicles in the total pollution have varied widely, as have assessments of the contributions of different types of vehicles to the total vehicular pollution.

The first major study was carried out in 2008 by the Central Pollution Control Board (CPCB) with the National Environmental Engineering Research Institute (NEERI). It identified road dust as the biggest contributor (52.5%) to particulate matter in Delhi’s air, followed by industries (22.1%). The study attributed only 6.6% of particulate emissions to vehicles. For NOx, the study found industries contributed 79% and vehicles 18%; vehicles were the main source for CO and hydrocarbons: 59% and 50% respectively.

The CPCB-NEERI findings were by and large reiterated by another government study two years later by the System of Air Quality Forecasting and Research (SAFAR) under the central Ministry of Earth Sciences. Results of the study that ascertained the sources of particulate matter during the Commonwealth Games in New Delhi in 2010, were published in the peer-reviewed journal Atmospheric Environment. It reached the “surprising” conclusion that “the unattended source of windblown dust from paved and unpaved roads” was the major contributor to PM 10 emissions. SAFAR Program Director Dr Gufran Beig said, “We found the majority of PM 10 came from road dust. This was in contradiction to previous published studies which blamed vehicular pollution as the major source.”

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The study found the contribution of windblown dust to be more than all other sources — including vehicles, industries and cooking fuel — put together, and more than four times the share of transport emissions, which was the second biggest contributor. This, despite 2010 experiencing the wettest monsoon in Delhi since 1978, which would be expected to cause road dust to settle. Vehicular and industry sources continued to be the dominant sources of PM 2.5 in this study, followed by construction.

Both the 2008 amd 2010 studies disagreed with the white paper on air pollution in Delhi that the union Ministry of Environment and Forests published in 2003. The white paper reported that between 1970-71 and 2000-01, the contribution of vehicles to Delhi’s particulate matter had increased from 23% to 72%.

Several other studies for the 1990-2008 period, and up to even 2010 and 2012, identified vehicles as the primary contributors to Delhi’s emission inventories. A study, Emission Estimates and Trends (1990-2000) for Megacity Delhi and Implications published in Atmospheric Environment in October 2004 found that over 80% of emissions of major pollutants including particulates, NOx and CO, came from the transport sector.

In 2013, Dr Sarath Guttikunda published a study in Atmospheric Environment that concluded that vehicular emissions contributed 90%, 54% and 33% to NOx, Total Suspended Particulate Matter and SO2 emissions respectively.

The same year, a study led by Dr Pramila Goyal of IIT-Delhi’s Centre for Atmospheric Studies flagged emissions from two wheelers as a “matter of concern”. Two wheelers contribute between 40% and 60% of the total pollution from vehicles, the study said. It identified Heavy Commercial Vehicles (HCVs) to be the major contributors to particulates (92%).

Other studies since 2007 have said that trucks contribute the lion’s share of pollutants like CO, SO2 and PM 2.5 in Delhi’s air.

Also in 2013, a UN Environment Program study by IIT Delhi and Dr Guttikunda that studied pollution inventories in three cities including Delhi, noted that “the steady increase and higher pollution levels (in the NCR) can be attributed to the exhaust emissions from trucks which are allowed to pass through the city after 9 PM.

“The high concentrations observed at night tend to linger during the rush hours through 11 AM combined with the passenger traffic and further exacerbating the exposure times and related health concerns along the major corridors.” The transport sector was found to contribute 17% and 10% of PM 2.5 and PM 10 respectively.

A 2015 IIT-Delhi and IIT-Bombay study by Dr Guttikunda and Dr Rahul Goel on vehicle exhaust emissions, which included transport policy recommendations for 2015-30, pointed out that trucks contribute more than 60% of total vehicular pollutants PM 2.5, CO and SO2 in the “greater Delhi region”.

The most recent study by IIT Kanpur, a two-year analysis submitted to the Delhi government last month, identified seasonal variations in contributions to particulates. In winter, the study attributed 46% particulate emissions to trucks, and 33% to two wheelers. Four wheelers trailed behind at 10%, followed by buses (5%) and Light Commercial Vehicles (4%). But in summer, the four top contributors of PM 10 are road dust, concrete batching plants, industrial point sources and vehicles. The top four contributors for PM 2.5 are dust, vehicles, domestic fuel burning and industrial pollution, the results of the study showed.

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  1. Jai Kumar
    Jan 6, 2016 at 10:07 pm
    Anybody who feels that car exhausts do not contribute to respiratory diseases should pipe their exhausts into the car and breathe in deep.
    1. R
      Jan 7, 2016 at 10:21 am
      Anyone who is this stupid must be an AAP! Learn to read, moron. If you read and cannot understand, then better to shut up.
      1. B
        Brahm Gaur
        Jan 6, 2016 at 11:57 am
        Indian roads are half bare and that causes lots of dust on roads. They leave dirt road on both sides of the roads to save money. Even the money spent on the roads does not fully go on the construction of the roads. The rods become pot s within 3 months. The Industries are not regulated properly. Indian government has not imposed minimum standards on the industries. That is the w cause of polluted air. They are putting their industrial waste in our rivers. Congress being a secular party never imposed any standards on the waste disposals. We are ending eating and smelling poison every day. India is great.
        1. Dennis Panakal
          Jan 7, 2016 at 5:56 am
          In a few years from now, Delhi befit to stands out as the most polluted city on earth beating even Mexico and other densely poted US cities who're but mainly the major contributors of CO2---[ In 2013, CO2 accounted for about 82% of all U.S. greenhouse gas emissions from human activities]. Clearly there is a far bigger problem looming larger globally in terms of an impending danger that threatens life on earth. But, look at the modern man and his mindless progressive march?With a kind of exploitative hard-drive in hand, the system functions even at the cost of total destruction. It intended to exploit the earth in w as if he [man] has an inbuilt program well configured with a goof-proof IP domain. Alternatively, he'd also find out "Yoga" as his prime source for some fresh air, agility and mental flexibility in order to further much of his destructive motives. So, let all the mindless bullies keep on practicing Yoga everyday to save their lungs from inhaling toxic gases.
          1. madhusudhan haravu
            Jan 7, 2016 at 1:39 pm
            All these studies seem to indicate that cars contribute the least to pollution in Delhi. Then in that case why have cars alone been targeted with people being forced off the roads by the threat of fine of Rs.2000. This means that the odd even policy has been formulated on entirely wrong umptions and is a completely flawed initiative. No wonder the forced stoppage of half of all cars on Delhi roads has not resulted in any decrease in pollution levels. Certainly sections of the the media owe an explanation as to how they became cheer leaders of this bad plan without checking the research findings.Hopefully the Delhi High Court will s the plan tomorrow.
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