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.

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 than WHO'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 their PM2.5 micrograms per cubic metre annual average.

1. Delhi, India, 153

A thick blanket of smoke is seen against the setting sun at a garbage dump in Delhi, India, on Oct. 17, 2014. (Altaf Qadri/AP)

2. Patna, India, 149

Passengers hang from the doors of the coaches of an overcrowded train at Parsa Bazar railway station in Patna, Bihar state, India, on Monday, Nov. 16, 2015. People travel home from Bihar in large numbers for Chhath, one of the most significant festival for people in the region. (Aftab Alam Siddiqui/AP)

3. Gwalior, India, 144

India's cricketer Rudra Pratap Singh and Pakistan's cricketers Yasir Hameed and Shoaib Akhtar (left to right) pose for a picture during their visit to a fort in Gwalior, India on Nov. 14, 2007. (Adnan Abidi/Reuters)

4. Raipur, India, 134

A woman labourer spreads black ash over a newly constructed road at Raipur, in the western Indian state of Gujarat, on Jan. 9, 2013. (Amit Dave/Reuters)

5. Karachi, Pakistan, 117

People sit by a fire to keep themselves warm amid a thick fog that blanketed some areas in Karachi, Pakistan, on Jan. 9, 2015. (Fareed Khan/AP)

6. Peshwar, Pakistan, 111

Pakistani travellers ride on a vehicle during a foggy day in Peshawar, Pakistan on Dec. 19, 2013. (A Majeed/AFP/Getty Images)

7. Rawalpindi, Pakistan, 107

A boy collects peanuts from a garbage dump site in Rawalpindi, Pakistan on Dec. 27, 2013. (Mian Khursheed/Reuters)

8. Khoramabad, Iran, 102

An Iranian man covered in mud stands near a fire to dry himself during the Ashura religious festival in Khorramabad, Iran on Jan. 7, 2009. (Morteza Nikoubazl/Reuters)

9. Ahmedabad, India, 100

Auto rickshaws drive along a national highway on the outskirts of Ahmedabad, India, on Dec. 2, 2015. (Amit Dave/Reuters)

10. Lucknow, India, 96

An Indian woman carries a bundle of dried branches and walks past a mound of garbage on the outskirts of Lucknow, India, on Sept. 24, 2015. (Rajesh Kumar Singh/AP)

The highest listing for Canada goes to Red Deer, Alta., with 14 PM2.5 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.