Scientists who conducted the study, published in the Environmental Science and Technology journal, said most of these deaths were due to heart attacks and strokes, and not very many because of respiratory diseases.The study, Addressing Global Mortality from Ambient PM 2.5, found that more than 45% of these premature deaths in Delhi could be avoided if the city met the national ambient air quality standard for PM2.5. In fact, if the city’s air could be cleaned up to the safe standards set by the World Health Organization, as much as 85% these deaths could be avoided, the experts said.Across India, as many as 4 lakh premature deaths per year could be prevented if the WHO standards were met. If no action is taken to bring down the current PM2.5 levels, deaths from air pollution would increase by 20% to 30% in India, the study warned.Scientists arrived at the potential to prevent premature deaths in Delhi assuming that the annual mean PM2.5 level in Delhi was about 150 micrograms per cubic metre, about four times the national standard and 15 times the WHO guideline.The study is authored by Joshua S Apte from the University of Texas, Julian D Marshall from the University of Minnesota, Aaron J Cohen from Health Effects Institute and Michael Brauer from University of British Columbia.It found as many as 2.1 million deaths per year could be prevented globally if air quality met the WHO guideline of 10 micrograms per cubic metre.An earlier study called the Global Burden of Disease (GBD) had estimated that high levels of PM2.5 particles, which can get lodged in the lungs and enter the bloodstream, were responsible for 3.2 million deaths globally. The current study uses a high-resolution global model to estimate how many deaths can be prevented, and in which parts of the world, using data from the GBD as well as following the methods of the GBD study.“The number one killer from air pollution, particularly PM2.5, is not respiratory diseases but ischemic heart disease and strokes,” co-author Apte told TOI.About 1.4 million premature deaths can be avoided in China and India alone if air quality met the WHO guideline, the study found.Authors of the study said making small reductions in PM2.5 concentrations would not help prevent a majority of deaths. The PM2.5 levels need to be maintained as per WHO guidelines or even lower for best gains. “If you do a little bit to reduce pollution you don’t get anywhere near what you get if you reduce the levels in a major way,” said Marshall.Interestingly, researchers found mortality rates can be substantially reduced even in places with a lower PM2.5 level, indicating that even low PM2.5 levels can cause mortality. “We were surprised to find the importance of cleaning the air in not just the dirtiest parts of the world which we expected to find, but even in cleaner environments like US, Canada and Europe,” added co-author, Marshall.The study found mortality in China due to air pollution as well as annual mean levels to be much higher than India. This, scientists said, was also because ground level air pollution data was much more robust and easily available in China. The estimates for India were conservative due to limited monitoring data.