At least 74% ultrafine particles (PM2.5) in Delhi’s air come from outside the city during summers, a study by the Energy and Resources Institute (TERI) has found.
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At least 74% ultrafine particles (PM2.5) in Delhi’s air come from outside the city during summers, a study by the Energy and Resources Institute (TERI) has found. They come from NCR towns located further north or west of Delhi and beyond even from as far as Pakistan, Afghanistan and Oman.
Delhi also contributes to 40% pollution in Noida and 15% in Gurugram during winter. The two satellite towns are located in Delhi’s downwind path. Panipat is located on the upwind path of Delhi and receives only 1% pollution from Delhi.
Ultrafine particles are 30 times finer than thickness of human hair and can penetrate deep inside lungs if inhaled. They can cause a range of cardiac and bronchial ailments.
“During summers, at least 74% of Delhi’s PM2.5 load comes from sources located outside the city and during winters external sources contribute around 64% of these ultrafine particles,” said TERI’s earth science and climate change division associate director Sumeet Sharma.
As much as 33% fine particles come from outside the country during summers. Around 17% of the pollutants come from areas outside the NCR. Roughly NCR towns contribute to around 24% of these particles. Delhi generates only around 26% of its own pollution.
The proportions change and around 64% of the city’s pollution comes from external sources in winters. Out of it, around 13% pollution comes from outside India.
“The contribution of external sources has been found to be more when it comes to PM2.5 pollution compared to PM10, which are coarser particles. External sources contribute just around 28% and 11% of the PM10 load during summer and winter,” said Sharma.
TERI conducted the study – ‘Source Apportionment of PM2.5 & PM10 of Delhi NCR for Identification of Major Sources’ – between November 2016 and March 2017 along with Pune’s Automotive Research Association of India.
India’s pollution forecasting wing, System of Air Quality Weather Forecasting and Research, had said that 40% of dust had come from west Asia in November 2017 when the air quality had dipped in Delhi.
In the first week of August, a dust storm in Oman pushed up Delhi’s pollution levels. Earlier, scientists had found salt particles from Pakistan and Afghanistan in Delhi and NCR.
“But this does not mean that we can sit idle. A lot can be done to curb the local sources such as dust and vehicle emissions in Delhi,” said Sharma.
The TERI study found secondary particulates contributed significantly to both PM10 and PM2.5 in winter. An earlier Indian Institute of Technology (IIT) Kanpur study had found around 20% of the city’s
PM2.5 pollution comes from vehicles.
“But we have found that the transport sector is contributing as much as 30% to the city’s PM2.5 load. This is higher than the contributions of transport sector reported in IIT Kanpur (2015) report, because in this study we included secondary particulates along with the primary contributions,” said Sharma.
In its draft comprehensive action plan, the Environment Pollution Control Authority has warned that secondary particulate matter, particles that are born out of the primary source air pollutants, pose as an additional threat to Delhi.
Primary particles such as SO2 and NO2 are directly released into the air from vehicles and industries. Secondary particles such as sulphates, nitrates and organic aerosols form in the air from these primary particles. They are equally harmful.
