The states with the dirtiest air will surprise you

Sorry, California.

The Golden State has the worst air quality of any state in the US, according to a new report from the United Health Foundation. The report measured air quality by the average person’s exposure level to airborne particulate matter (PM). More specifically, it’s a measure of how much particulate matter is present in a cubic meter of air.

Most airborne particles are coarse, and can actually be seen in the air as soot or smoke. But it’s the finer particles, or those less than 2.5 microns in diameter, that pose the greatest health risks: They can become lodged deeply in a person’s lungs or bloodstream and can cause a host of ailments. Cars and heavy industry are the biggest contributors.

The US has an overall average of around 9.5 micrograms per cubic meter of PM2.5 (as the particles are known), well below the WHO’s safety guidelines of 25 micrograms per cubic meter.

But California has a higher rate of the particles in the air than any other state, with an average of 12.5 micrograms per cubic meter. Idaho, Pennsylvania, and Indiana followed closely, according to the report. On the other hand, states like Wyoming and North Dakota have exceedingly clean air.

See how your state compares:

Why such bad air in the Golden State?

California’s bad air is partially due to residents’ reliance on cars for transportation. Agricultural burning also spews huge amounts of particulates into the air.

But California’s geography is also to blame. The Central Valley contains some of America’s best farmland — and some of its worst air. The mountains around the valley act as a ‘pool’ for the airborne particulates. An inversion of warm air keeps the particles stuck, according to CityLab.

And California’s ongoing drought only exacerbates this problem, contributing more dust to the atmosphere.

Still, while California may have some pretty bad air, it pales in comparison to Beijing, which reported over 600 micrograms per cubic litre on Monday, the eve of the climate talks in Paris.

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