Local sources of pollution such as traffic, construction, and domestic heating contribute significantly to the Delhi National Capital Region's high concentrations of harmful air pollutants, a new comprehensive study suggests.
Researchers from the University of Surrey in the UK noted that given the dominance of local sources, efforts to control pollution are needed throughout the year, not just during winters, when the problem reaches its peak. According to the World Health Organisation (WHO), air pollution is estimated to cause nearly 4.2 million premature deaths worldwide in 2016, the researchers said.
In India, around 600,000 deaths annually are attributed to air pollution, and some of the world's highest levels can be found in Delhi city, they said. The study, published in the journal Sustainable Cities and Society, gathered four years of pollution data from 12 sites across Delhi, Haryana and Uttar Pradesh.
The researchers analysed how particulate matter -- PM2.5 and PM10 -- and gases such as oxides of nitrogen, sulphur dioxide, carbon monoxide, and ozone impact this region of the country. They found a clear trend with significantly higher levels of air pollutants in winter months than in summer or monsoon periods, with the exception of ozone levels.
The high levels of fine and coarse particulate matter (PM2.5 and PM2.5-10) in winter months were attributed to fumes from crop burning upwind of Delhi, and a likely increase in biomass burning for residential heating because most parts of the region do not have central heating systems.
The weather during winter months -- particularly reduced precipitation and low wind speeds -- is also thought to play a significant role in raising pollutant levels.
The team also obtained meteorological data from each station for the duration of the study, allowing the examination of wind speeds and the direction of particulate matter. The analysis suggests that local sources of pollution, such as traffic, construction and domestic heating, influenced pollutant levels more than regional sources like air pollution from long-range traffic coming from outside the region.
"It is heartening to see the world come to terms with the fact that the climate change emergency should be at the top of every nation's agenda -- not least India," said Professor Prashant Kumar, from the University of Surrey.
"Our analysis of Delhi's air pollution data over a significant period of time confirms that local sources of pollution -- such as traffic and the heating of homes -- are having a tremendous impact on air quality in the Delhi region.
"Moreover, the surrounding regions of Delhi are suffering substantial impacts during winter periods," Kumar said.
He noted that currently configured network of air pollution monitors does not permit the evaluation of long-range transport between Delhi and the NCR and vice versa.
This highlights a need for well-thought-out planning to expand the current network in the future.