Air pollution has returned to haunt Delhiites and this time it appears to be more lethal than ever.Residents of the national Capital, who were breathing easy after the introduction of CNG and green vehicles in the past few years, have reason to worry about the air they inhale. A recent study by Jawaharlal Nehru University (JNU) has revealed that the air in Delhi is full of carcinogenic (cancer causing) particles.JNU's department of environmental sciences has come out with a toxicological risk assessment report that points out alarming levels of aerosol and heavy metals in the city's air. The study was sponsored by the University Grants Commission and supported by the Ministry of Environment and Forests and published by the National Academy of Sciences recently.The presence of particulate matter (PM), inhalable particles, in both diameter - PM2.5 and PM10 - and cancer causing heavy metals such as nickel and cadmium in the Capital's air has been found to be exceeding the permissible limits at peak traffic hours.The concentration of PM2.5, in fact, has been found to be exceeding the limits (60ig/m3) prescribed by the Central Pollution Control Board in all areas. The effect of exposure to these pollutants on the health of population was studied in the age-group of 18-45. "Exposure to PM10 for eight hours daily for 10 years can cause 1,820 early deaths (in the 18-45 age group) per one million population due to acute diseases such as respiratory ailments. If people are exposed to PM2.5 (for the same period), there is a possibility of increase in number of early deaths by 2,170 people per one million population," said Rajesh Kushwaha, a research scholar at the School of Environmental Sciences, JNU."Early deaths triggered by chronic diseases such as heart diseases and cancer would increase by 47,800 per one million population from exposure to PM2.5 and 42,300 from PM10. At least 5,790 more people would die due to exposure to nickel, while an additional 869 people would die due to exposure to cadmium," he said.Vehicular emissions contribute about 63 per cent to the total pollution, followed by industries and thermal power plants (29 per cent) and domestic sector (8 per cent), says the study."It is estimated that about three million deaths occur globally every year due to air pollution, mainly by particulate matter. People exposed to air pollutants for longer durations may run an increased risk of cancer or serious health disorders," said Kushwaha.The areas selected for the research were Hauz Khas, Dhaula Kuan, areas surrounding JNU, Okhla and Kaushambi in NCR.Fifteen samples were collected and each sample was analysed chemically (for metals). The maximum (2,118.45 ig/m3) presence of particulate matter was observed at Okhla and the minimum (490.17 ig/m3) in areas near JNU. Among heavy metals, presence of lead, manganese and nickel was maximum at the five locations.Okhla was the most polluted area and JNU (forest area) the least. Lead, nickel, cobalt were dominant metals in Okhla air, while Kaushambi, a fully residential area located near a waste site and national highway, recorded high presence of lead, manganese and nickel. Alarmingly high concentration of cadmium was observed in Okhla."We used a scientific method for calculating the estimated number of deaths that would take place if the populations are exposed to the pollutants," said Kushwaha.Government officials expressed surprise over the alarming presence of heavy metal in the city's air."This is very unusual that nickel and cadmium have been found in Delhi's air. The main source of these metals is industries. Though the factories are not in abundance in Delhi, they have emerged as a big source of health concern. This is a serious matter and should be seriously pursued," said Dr T.K. Joshi, director, Occupational and Environmental Programme, Delhi Government.The findings of the report have also perturbed city's environmentalists. "We know that particulate matter level is high in Delhi's air, but the high presence of heavy metals in shocking. The findings show how toxic can PM be when it mixes with other compounds in the air," said Anumita Roy Chowdhury, executive director, research and advocacy, Centre for Science and Environment. "The mortality risk assessment calls for better pollution control measures by the authorities. It's high time that we ramp up our actions towards air pollution control in the city," she said.