World's deadliest air: Delhi's air pollution 10 times higher than WHO limits, survey finds - As if there were not enough difficulties in Delhi to impair its citizens, the findings of a recent air quality monitoring survey - released on Monday by Greenpeace - have found that the deadly PM2.5 levels in the national capital are 10 times higher than the safety limit prescribed by the World Health Organization (WHO), and four times more than even the Indian safety limit.

The air in Delhi is the most toxic in the world due to high concentrations of PM2.5 - particulate matter less than 2.5 micrometres in diameter - that is believed to pose several health risks because it penetrates deeply into lungs.

The PM2.5 limit prescribed by the WHO is 10 micrograms per cubic metre, while the Indian limit is 40 micrograms per cubic metre. PM2.5 are miniscule particles in the air that cause the air to appear hazy, affect respiratory tracts and reduce visibility.

According to a new study, air pollution is killing 3.3 million people a year across the world. Farming plays a big role in smog and soot deaths in industrial nations.

Scientists in Saudi Arabia, Cyprus, Germany and at Harvard University calculated the most detailed estimates of the toll of air pollution, looking at what caused it. The study indicated that if trends do not change, the yearly death toll will double to about 6.6 million a year by 2050.

Lead author Jos Lelieveld, at the Max Planck Institute for Chemistry in Germany, said three-quarters of the deaths are from heart attacks and strokes.

With 1.4 million deaths a year, China has the most air pollution casualties, followed by India with 645,000, and Pakistan with 110,000. The U.S, with 54,905 deaths in 2010 from smog and soot, ranks seventh highest for air pollution deaths.

As per the study, in Europe, Japan, Russia, South Korea and northeastern U.S., agriculture is the number one cause of the soot and smog deaths. Worldwide, agriculture is the number two cause with 664,100 fatalities, behind the more than 1 million deaths from cooking and in-home heating with wood and other biofuels in the developing world.

Lelieveld said the problem with farms is ammonia from fertilizer and animal waste. That ammonia combines with sulfates from coal-fired power plants and nitrates from car exhaust to form the soot particles that are the big air-pollution killers.