Think Beijing's air pollution is bad? These 10 cities are worse

With some residents in Beijing taking a so-called smog holiday on Tuesday, you might think (or hope) that air pollution couldn't get any worse in the world.

Well, think again, because according to the annual averages of air pollution in a 2014 World Health Organization report, Beijing doesn't even crack the top 20.

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While Tuesday's readings of PM2.5 particles climbed above 300 micrograms per cubic metre, the city's yearly average is closer to 56 micrograms per cubic metre. That's still more thanWHO's designated safe level of 25.

Thirteen out of the top 20 worst cities for air pollution are in India, while three are in Pakistan. Here are images from the Top 10 according to theirPM2.5 micrograms per cubic metre annual average.

1. Delhi, India, 153

2. Patna, India, 149

3. Gwalior, India, 144

4.Raipur, India, 134

5. Karachi, Pakistan, 117

6.Peshwar, Pakistan, 111

7.Rawalpindi, Pakistan, 107

8.Khoramabad, Iran, 102

9.Ahmedabad, India, 100

10.Lucknow, India, 96

The highest listing for Canada goes to Red Deer, Alta., with 14PM2.5 micrograms per cubic metre. Montreal and Calgary are listed at 11, while Toronto squeaks in with 8.

WHO adds that rankings based on PM2.5 particles is a useful metric, it isn't the only one to measure air pollution, and that "there is no comprehensive, world-wide database" to definitively rank the most polluted cities. It also includes regular rankings of the slightly larger 10PM particles per cubic metre in its regular reports.