The most polluted city in the world isn’t Beijing or Delhi
Indian commuters travel through a traffic jam on their way to New Delhi from Gurgaon on May 3. (Chandan Khanna/AFP/Getty Images)
What's the most polluted city in the world? Some might point to Beijing, the Chinese capital, and its now
legendary smog problem. Others may point towards India, where Delhi's own air pollution problems
are become similarly infamous. However, a new report from the World Health Organization suggests that these megacities are actually only the tip of the iceberg – and the actual city with the world's worst pollution is probably in Iran.
We say "probably" here for two reasons. First, not all cities collect good enough data to be measured (a problem in itself). And secondly, it depends on how you measure it. When studying air quality, scientists look at the size of particles found in the air. Generally, a lot of attention is placed upon particles of a PM2.5 size, which is around one-30th the size of a human hair. These particles are particularly worrying because they have the ability to enter lungs and blood tissue and cause serious health problems.
However, you can also measure larger particles in the air. At PM10, the particles are coarser, though they can still be inhaled and cause health problems.
If you look at WHO's PM2.5 data, the Iranian city of Zabol comes out on top. This city, which has a population of more than 100,000, sits on the border with Afghanistan in Iran's east. The city is known for the "120 day wind," a lengthy dust storm through the hot and dry summer. Zabol is followed by Gwalior and Allahabad, two Indian cities, while Riyadh, Saudi Arabia's capital and largest city, comes in fourth.
Cities by PM2.5 pollution
Zabol (Iran) 217
Gwalior (India) 176
Allahabad (India) 170
Riyadh (Saudi Arabia) 156
Al Jubail (Saudi Arabia) 152
Patna (India) 149
Raipur (India) 144
Bamenda (Cameroon) 132
Xingtai (China) 128
Baoding (China) 126
Annual mean PM2.5, ug/m3
Source:
World Bank
THE WASHINGTON POST
Delhi comes 11th in this ranking, while Beijing is far down the list at 57. For reference, WHO suggests that
10 micrograms per cubic meter of PM2.5 should be a guideline level for safe air.
WHO's PM10 data paints a somewhat different picture. Nigeria's Onitsha, a city of half-a-million people on the Niger River, is atop this list. The city has been known for its rapid growth and gridlock, though some locals were apparently still surprised that it appeared so high on the list. “We know pollution is very bad here. But this city must be much better than Lagos,” Solomon Okechukwa, a local official, told
the Guardian.