Delhi's rising pollution levels are posing a threat to the longevity of its residents and reducing their lifespan by nearly 6.3 years, a study conducted by the Indian Institute of Tropical Meteorology (IITM) has revealed.

The exposure  to PM2.5 (fine particulate matter of the size of 2.5 microns) is leading to the loss of 3.3 years from an average Indian's life, and nearly 6.3 years from a Delhi resident's life, the Indian Express reported, citing the study.

According to the World Health Organisation, the PM 2.5 levels of Delhi were reported to be 153 micrograms per cubic metre (µg/m³), which is three times the pollution level in Beijing, China, and 10 times the average pollution levels in New York.

The study, published in the online journal Geophysical Research Letters, was conducted by IITM in collaboration with the National Center for Atmospheric Research, Boulder, Colorado, in the U.S. and the Atmospheric Chemistry Observations and Modeling Laboratory.

IITM scientist and study co-author Sachin Ghude was quoted by the IE as saying people living in the states of West Bengal and Bihar are also at an increased risk of reduction in life expectancy due to PM2.5 exposure.

"Air pollution is cutting the lives of those living in polluted states of West Bengal and Bihar by 6.1 years and 5.7 years, respectively," Sachin said.

He added that although there is still no clear method to predict the number of deaths caused by air pollution, the study results are in line with global health surveys.

"The methods used in this study rely on statistical algorithms to construct estimates about a population's response to pollution exposure using previous concrete observations on pollution and public health. The problem is that most of these observational studies have taken place in regions with comparatively low pollution levels, such as Europe or the U.S. We don't have any epidemiological studies in India that look at the long-term effects of air pollution on mortality," Sachin told IE.

He further said the researchers in this study have analysed human responses to high pollution levels and compared them to the responses of humans who live in less polluted areas.

"It is the only available option for this type of research until the studies are conducted in India," he said.

The study also found that the states of Maharashtra and Uttar Pradesh accounted for the highest number of premature deaths in India due to PM 2.5 pollution, the Times of India reported.

"Premature mortalities due to PM2.5 is 5.7 lakh and from ozone was 12,000 for 2011. Exposure to these led to economic loss of approximately $640 billion. Exposure to fine particulate matter in the air also reduces life expectancy by about 3.4 years," Sachin was quoted by the TOI as saying.