Why Delhi is pollution hotspot in winter: winds from outside

New study finds tiny particles blow in from Pak, Punjab, Haryana on one side and UP, Bihar on other.

Written by Mallica Joshi | New Delhi | Updated: November 11, 2016 7:41 am
air pollution, supreme court, delhi pollution, delhi smog, delhi government, environment ministry, ngt, national green tribunal, pollution delhi, air quality delhi, indian express, india news In winters, 72% of wind comes from northwestern parts of India and Pakistan, 28% from Indo-Gangetic plains.

WINDS THAT blow into Delhi, especially in winters, make it more prone to pollution from Pakistan, Punjab and Haryana on one side, and Uttar Pradesh and Bihar on the other, according to a new study.

The study found that in winters, 46 per cent of Particulate Matter 2.5 (PM 2.5) — tiny toxic dust particles — blows into the capital from the northern part of India and Pakistan, and 30 per cent from UP, Bihar and Uttarakhand.

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Both sets meet in and around Delhi, making the region a hotspot for particulate matter pollution, the scientists found. The findings are in sharp contrast to the statement made earlier this week by Union Environment Minister Anil Madhav Dave, who said that Delhi was responsible for 80 per cent of pollution in the state.

The study was conducted by researchers Mohit Saxena, A Sharma, Saraswati, T K Mandal, S K Sharma, C Sharma from the National Physical Laboratory (NPL) and Priyanka Saxena from National Environmental Engineering Research Institute (NEERI). The Delhi-based NPL, which is India’s measurement standards laboratory, and NEERI come under the Council of Scientific and Industrial Research (CSIR).

The study — Water soluble inorganic species of PM 10 and PM 2.5 at an urban site of Delhi, India: Seasonal variability and sources — was published in October in the peer-reviewed science journal Atmospheric Environment. The journal is published by Elsevier, which also brings out The Lancet.

The study found that 72 per cent of Delhi’s wind in winters comes from the northwestern parts of India and Pakistan, while the remaining 28 per cent comes from the Indo-Gangetic plains. The wind patterns in winters, summers and monsoons are different and so is the way PM 2.5 travels, according to the researchers who conducted the study.

“PM 2.5 mass concentration in summers was (52 per cent) because of the trajectory (of winds) travelling across southern Afghanistan, northwestern Pakistan and (35 per cent) from the eastern part of India. In winter and spring seasons, the sampling site was affected by cold air masses arriving from the northern parts of India and Pakistan (46 per cent) and (30 per cent) from the adjoining states of Delhi (Uttarakhand and Uttar Pradesh),” the study found.

“It is significant to mention that adjoining areas of Delhi are the industrial hubs, construction and agriculture zones, therefore these activities probably result in the inflow of a mixture of coarse and fine continental pollutant aerosols to the study area,” says the study.

In monsoons, 53 per cent of wind comes from the Indo-Gangetic Plains (east of Delhi), 25 per cent from Afghanistan, Pakistan and northern India, and 22 per cent from the Arabian Sea.

The study was conducted primarily to understand the variation in chemical composition and physical properties of pollutants that reach Delhi from the arid and semi-arid regions west and north of the capital, depending on the season. The samples were collected from the NPL premises on Pusa Road in Delhi between January 2013 and December 2014.

NPL had also conducted a source apportionment study, published in May, which showed that 14 per cent of PM 2.5 in Delhi’s air is because of biomass burning. Secondary aerosols (particles formed by the interaction of gases with elements in the air) accounted for 21.3 per cent of PM 2.5. This was followed by soil dust at 20.5 per cent, vehicle emissions at 19.7 per cent, fossil fuel combustion at 13.7 per cent, industrial emissions at 6.2 per cent, and sea salt at 4.3 per cent.