Here are some of the cities with the highest levels of pollution:
1. Delhi, India
According to a credible international news agency, there are roughly 8.5 million registered vehicles in the city cause excessive air pollution in Delhi mainly by industry and vehicular traffic.
2. Patna, India
The second largest city in eastern India, Patna has an estimated population of 1.68 million as of 2011. It is a major agricultural center of trade, with its most active exports being grain, sugarcane, sesame and rice.
3. Gwalior, India
Gwalior, one of the largest cities in central India, is surrounded by three main industrial and commercial areas: Sitholi, Banmore and Malanpur.
4. Raipur, India
Raipur has become an important regional commercial and industrial destination for the coal, power, steel and aluminium industries and is the largest market of steel in India.
5. Karachi, Pakistan
The air in the city is rapidly polluted by vehicle emissions from rickshaws and buses, industrial emissions, open burning of garbage and house fires.
6. Peshawar, Pakistan
Vehicular emissions, industrial and brick kiln emissions, the burning of solid waste and refuse and the use of ill-maintained vehicles are some of the sources of pollution in Peshawar.
7. Rawalpindi, Pakistan
A rapidly growing city in the Pothohar region of northern Punjab, Pakistan, Rawalpindi is home to various textile mills. Its high levels of traffic have pushed up air pollution in the region.
8. Khorramabad, Iran
In 2012, pollution contributed to the premature deaths of 4,500 people in Tehran and about 80,000 across Iran, according to the health ministry.
9. Ahmedabad, India
Ahmedabad has become an important economic and industrial hub in India and it is the second largest producer of cotton in the country. Heavy construction work for both infrastructure and housing has contributed to high levels of air pollution.
10. Lucknow, India
The capital city of Uttar Pradesh is among the most polluted cities in the country. The lack of transport infrastructure and growing number of vehicles exacerbates the problem, according to India’s Centre for Science and Environment.