Top Ten Most Polluted Cities in the World

Here are the top 10 cities for which data is available, according to a 2011 World Health Organisation (WHO) report.

The  is measured as the microgramme (mcg) concentration per cubic metre of air of particulate matter smaller than 10 micrometres (PM10)—about a seventh of the width of a .

The figures are the average for the year. Seasonal spikes can be many times higher.

The WHO's health guidelines are maximum exposure of 20 mcg/m3, measured as an annual average.

1) Ahvaz, Iran 372 mcg/m3 (2009 data)

2) Ulan Bator, Mongolia 279 mcg/m3 (2008 data) 

3) Sanandaj, Iran 254 mcg/m3 (2009 data)

4) Ludhiana, India (2008 data) and Quetta, Pakistan (2003/4 data)

tied at 251 mcg/m3

5) Kermanshah, Iran 229 mcg/m3 (2009 data)

6) Peshawar, Pakistan 219 mcg/m3 (2003/4 data)

7) Gaborone, Botswana 216 mcg/m3 (2005 data)

8) Yasuj, Iran 215 mcg/m3 (2009 data)

9) Kanpur, India 209 mcg/m3 (2008 data)

10) Lahore, Pakistan 200 mcg/m3 (2003/4 data)

Paris, whose levels hit a high of 180 mcg/m3 last week, has an annual mean level of 38 mcg/m3 according to 2008 data.

Beijing, which has also been in the news over smothering smog, is listed with an annual mean figure of 121 mcg/m3.

The Middle East and North Africa is the world's most polluted region with an annual mean level well over 130 mcg/m3, followed by Southeast Asia with a level near 100 mcg/m3.

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