Pollution in east, north and central Indian cities primarily comes from residential and transportation sectors, while in western India, industry and energy are the main contributors to local PM2.5 pollution, a study has found.

Published in the journal Modeling Earth Systems and Environment, the study also found that PM2.5 pollution in cities in south India majorly comes from the industry and residential sectors.

Researchers from the Indian Institute of Tropical Meteorology, Maharashtra, and the Indian Institute of Technology Roorkee, analysed pollution levels in 53 cities, having more than a million population during the winter of 2015-2016.

Residential emissions -- from burning biomass for cooking and heating -- were found to be the leading contributor to local PM2.5 pollution in Srinagar (68 per cent), Varanasi (37 per cent), Allahabad (34 per cent) and Kanpur (33 per cent).

The transportation sector's contribution to local PM2.5 pollution was found to be higher in north Indian cities, especially Delhi and Ghaziabad.

North and east Indian cities also recorded higher local pollution levels, compared to cities in central India, with the highest seen in Delhi, Ghaziabad and Kolkata, the researchers said.

Further, pollution levels in the cities of west and south India were relatively lesser, compared to those in north and east Indian cities, they said.

The highest local PM2.5 pollution was, however, observed in Greater Mumbai, where absolute contributions of industrial, energy and residential sectors were also higher than those in the cities of west and south India.

In another study, researchers from Berhampur University, Odisha, and the Indian Institute of Science, Bengaluru, analysed the transport, residential and power sectors for specific components that they contribute to PM2.5 pollution, such as nitrogen and sulphur oxides.

Vehicular emissions remain "the dominating source" of nitrogen oxides and volatile organic compounds (gases in products like disinfectants and paints), while residential and power sectors are the highest emitters of carbon monoxide and sulphur dioxide, the authors found.

Indo-Gangetic Plain (IGP) and half of the districts contribute about 45 per cent and 80 per cent of carbon monoxide emission, the study published in the journal Environmental Pollution found.

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