Dirty air sending millions to early grave — study

In Russia, the eastern United States and east Asia, agriculture was responsible for the bulk of pollution with fine particles under 2.5 microns in size — small enough to easily penetrate the lungs.

A micron is a millionth of a meter.

Ammonia released by fertilizer combines with the dangerous sulfates and nitrates in car exhaust fumes, to make the tiny particles.

The combination is deadly in the Western world, said the team. Their calculations suggested car exhaust caused about 20 percent of pollution-related deaths in Britain, Germany and the US — while the global average is about five percent.

The team used computer models combining air quality measurements, population and health statistics and data on the health risks of breathing in pollution.

Lelieveld said the study offered the most complete picture yet as it included data on the risks in heavily-polluted places such as parts of China, while previous research relied mainly on conditions in the United States and Europe.

Humans are not the sole source of deadly air pollution on Earth — desert dust was linked to at least one in 10 deaths, the team added.