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Preeti Kashyap


Monday, July 5, 2021
Dust, fuel combustion among Delhi’s chief summer pollutants, finds stud
Correspondent : Soumya Pillai
Breaking down the suspended particulate matter of the size of 2.5 microns or PM2.5 — the primary air pollutant in Delhi — into three components, a new study by Indian Institute of Technology(IIT), Kanpur has identified dust, solid fuel combustion, vehicular emissions, garbage burning and cooking as some the leading sources of pollution in the Capital during summer.

The study titled ‘Realtime quantification and source apportionment of fine particulate matter including organics and Elements in Delhi during summertime’ will be released on Monday. HT has seen the report.

This is the first real-time pollution source apportionment study in the capital. Experts say such studies are important to understand and identify the sources of pollution in a particular area and help authorities plan specific interventions in real-time.

Instead of treating PM2.5 as one entity, the researchers broke it down into several sub-categories -- organic aerosols, elements, black carbon, sulphates, nitrous oxides, chlorine and nitrates. They said this helped in quantifying more accurately the proportion of each source in the total pollution mix.

Professor SN Tripathi, head of department (civil engineering), IIT-Kanpur, and member of National Clean Air Programme, said highly advanced equipments were used for this study that helped the researchers not only understand the sources of pollution, their share, and even their location.

“The technology used for this study has given us data every hour, which has helped us better understand the sources and how these are impacting Delhi’s air. We have also been able to identify more sources, such as cooking that were ignored in earlier source apportionment studies,” said Tripathi.

The study showed that secondary oxidised pollution particles, which are formed as a result of pollutants reacting with the molecules in the atmosphere, had a share of 64% in the city’s organic aerosols (pollutants released from combustion of organic matter such as vehicular fumes, cooking etc), and 27% elements (metals particles suspended in the air emanating from power plant emissions, industrial waste burning, etc) during June and July.

The study showed that three major factors contributed organic aerosols in Delhi’s air during summers--vehicular emissions had 12.3% share, solid fuel 16.2% and cooking, both in-house and in the open, released 7.3% of such aerosols.

Elements or metals came mostly from dust (52.5%), emissions from power plants (16.2%), garbage burning and emissions from steel industries (10.7%), solid fuel combustion (10.5%), non-exhaust pollution from reasons such as road dust, industrial waste burning (1.5%) and emissions from metal processing industries (1.4%).

“It was also found that the difference between the percentage composition of primary organic aerosols (from sources such as traffic, biomass burning and cooking) and secondary organic aerosols in the study was 28.4% as compared to only 4% in winters, indicating the dominance of secondary sources in summer,” the source apportionment study said.

Scientists said that while government agencies and pollution monitoring bodies focus on air pollution in winters when Delhi faces a public health crisis each year, it was also important to understand how pollution sources change and act differently during summer months so that a holistic pollution control plan can be implemented for the region.

In 2016, IIT-Kanpur conducted a similar source apportionment study for Delhi, giving a year-round analysis of sources contributing towards the city’s pollution levels. The study showed that during summer months, coal and fly ash (26-37%), soil and road dust (26-27%), secondary particles (10-15%), biomass burning (7-12%), vehicular emissions (6-9%) and municipal solid waste (7-8%) were the major sources of pollution in the city.

As opposed to earlier source apportionment studies that have been conducted for Delhi, the recent one gives out a high-resolution, real time analysis that gives a more accurate understanding of sources, researchers said.

The study has also marked the different areas from where pollutants come into the Capital to understand the share of pollution from local sources and sources located outside the city.

For instance, the study highlighted that small and medium metal processing units located in Punjab, Haryana and Pakistan were contributing significantly to chlorine in Delhi’s PM 2.5 levels.

Similarly, high contribution of crustal elements (such as aluminium, calcium, magnesium, potassium and iron) in PM 2.5 was seen during summer due to high intensity of dust storms blowing into the region from the deserts of Rajasthan.

Tripathi said that this study should be seen in the context of earlier source apportionment studies to get a complete picture of Delhi’s pollution graph. He said this will help government agencies and policy makers to understand what mitigation steps have helped and what more needs to be done.

“The idea is that we can’t do just one study of a region and be done with it. Data needs to be constantly updated with the use of latest technology. There are newer findings in this study that was never known before. With this policy makers will be able to better understand what was the scenario, have the pollution mitigation measures that were implemented based on earlier findings worked and what more needs to be done to fix the major pollution sources in the Capital,” Tripathi said.

Anumita Roychowdhury, executive director (research and advocacy), Centre for Science and Environment said that updated and real-time data on pollution contributors in Delhi were needed to formulate plans to tackle the sources.

“If we know details of what are the pollutants, what is it’s contribution and from where they are coming in, out preparedness to plug this will be much better. Seasonal analysis is also necessary because meteorology plays a very important role in changing the pollution profile of a region,” Roychowdhury said.

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