Patna, India, the World's Most Polluted City, Struggles With Air Quality Alerts

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5. Delhi, India
> Population: 26.5 million
> Average PM2.5 pollution per cubic meter: 122 micrograms
> Average PM10 pollution per cubic meter: 229 micrograms

Delhi, India is the second most polluted city in India and the fifth most polluted in the world. The average level of concentration of PM2.5 in Delhi is 122 micrograms per cubic meter of air. PM 2.5 air pollution is nearly seven times more concentrated in Delhi than it is in Visalia-Porterville, California, the most polluted metro area in the United States.

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4. Baoding, China
> Population: 1.1 million
> Average PM2.5 pollution per cubic meter: 126 micrograms
> Average PM10 pollution per cubic meter: 190 micrograms

The northeastern Chinese city of Baoding is one of 10 in the country to rank among the most polluted in the world. The highly concentrated air pollution in the city is largely attributable to coal-powered steam boiler systems used in villages around the outskirts of the city. Ironically, the city is one of several in the country to become a green energy hub, using renewable energy to power street lights. It is also home to one of the largest solar panel manufacturers in the world.

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3. Xingtai, China
> Population: 689,000
> Average PM2.5 pollution per cubic meter: 128 micrograms
> Average PM10 pollution per cubic meter: 193 micrograms

Xingtai is one of several cities in China’s Hebei province to rank among the most polluted in the world. Xingtai’s PM2.5 concentration of 128 micrograms per cubic meter is higher than any other city in both the province and the country as a whole. Coal mines and coal powered factories are largely to blame for pollution in the area. The problems are exacerbated by companies disregarding regulations aimed at reducing pollution in order to save money.

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2. Bamenda, Cameroon
> Population: 500,000
> Average PM2.5 pollution per cubic meter: 132 micrograms
> Average PM10 pollution per cubic meter: 141 micrograms

Bamenda, Cameroon has the most polluted air of any African city and the second most polluted air of any city in the world. The average annual concentration of PM2.5 in Bamenda is 132 micrograms per cubic meter of air, which is over seven times the concentration found even in the most polluted U.S. city. Pollution is so bad in Bamenda, that spending just 45 minutes on a congested roadway in the city could be enough to harm one’s health.

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1. Patna, India
> Population: 2.2 million
> Average PM2.5 pollution per cubic meter: 149 micrograms
> Average PM10 pollution per cubic meter: 167 micrograms

One of three cities in India on this list, Panta is also the most polluted city in the world. The average level of concentration of PM2.5 in Patna is 149 micrograms per cubic meter of air, more than eight times the concentration in Visalia-Porterville, California, the most polluted metro area in the United States. Vehicle emissions and smoke from coal burning brick kilns largely explain the high levels of pollution throughout the city.