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Saturday 9 March 2019

The world’s worst air pollution

By Chris Newell and Paul Caruana Galizia

Air pollution is a major environmental risk to our health. Particulate matter – a mixture of organic and inorganic substances in the air – affects more people than any other air pollutant.

Particulate matter of 2.5 microns or less in diameter – PM2.5 – penetrates the lung barrier and enters the blood system. It causes 4.2 million premature deaths a year, according to the World Health Organisation.

Some 837 million people live in cities with PM2.5 levels above 10 micrograms per cubic metre, which the WHO found increases heart and lung cancer mortality rates.

These people live in mega cities like Beijing, where air pollution is seven times higher than the WHO guideline, but also medium-sized cities like Liverpool and smaller cities like Brussels, where air pollution is almost double the WHO guideline.

The better news is that 92 million people live in cities with safe levels of PM2.5, from Toronto in Canada to Newcastle in England and Boulder in the United States.

Asian mega cities dominate the sample of highly polluted cities. The world’s five most polluted cities are all Indian: Kanpur, Faridabad, Gaya, Varanasi, and Patna. Their PM2.5 levels are around 16 times higher than the WHO guideline.

But the global picture is incomplete

Every city goes through peaks and troughs within a single day.  Take small, medium, and large cities in the UK. Pollution in Plymouth, a small city, is not much lower than in London, the largest city. Meanwhile, pollution in Bristol, a medium-sized city, is higher than London’s at various points in the day.

The same picture holds true for the US

Air pollution in tiny Hidalgo, a small and arid county in Texas, is higher than both Los Angeles and Baton Rouge, Louisiana. Part of the explanation could lie in the advances made by some big population centres in fighting air pollution through clean public transport.