A chilling look at the 10 most polluted cities in the world.

Between 2008 and 2013 alone, global pollution levels increased by 8%. In particular, approximately 80% of the world's cities are experiencing air pollution.

Air pollution in major cities is getting worse. According to the latest report from the World Health Organization (WHO), approximately 80% of the world's major cities are experiencing air pollution.

Pollutants that are harmful to human health are calculated using the PM 2.5 parameter (the concentration of particulate matter smaller than 2.5 micrometers in the air). These are found in coal dust, smoke, and other types of dust. PM 2.5 is particularly dangerous because it can become trapped in the airways, causing long-term health problems such as asthma or chronic lung disease.

Based on PM 2.5 data, the WHO has compiled a list of the world's most air-polluted locations for travelers to be aware of when visiting.

Zabol City, Iran: 217 µg/m3 PM 2.5

The city of Zabol, Iran, is considered the most polluted place in the world. Its pollution index also reaches the highest levels.

Gwalior City, India 176 µg/m3 PM 2.5

Gwalior City is a historic city located about 200 miles south of New Delhi. It is also one of the most polluted cities in India. The high levels of air pollution are due to the presence of coal-fired power plants and a large number of cars.

Allahabad city, India 170 µg/m3 PM 2.5

Another Indian city, Allahabad, also makes the list. With a population of nearly 1 million, the city is located near the Ganges River and is therefore known for its arid conditions.

Riyadh, Saudi Arabia 156 µg/m3 PM 2.5

Riyadh is the largest city in Saudi Arabia, and also the most air-polluted, with high levels of sulfur dioxide in the air due to industrial activities.

Al Jubail City, Saudi Arabia 152 µg/m3 PM 2.5

Al Jubail is an industrial city in the Persian Gulf region. Due to rapid industrialization since the 1970s, air pollution levels have increased significantly since the 1980s.

Patna city, India, 149 µg/m3 PM 2.5

Patna is the second largest city in eastern India and a major agricultural and commercial center. Pollution levels there stem from traffic, electricity, and other industries.

Raipur City, India 144 µg/m3 PM 2.5

Raipur is a city in central India and ranks fourth in the country in terms of pollution levels. The pollution stems from coal, aluminum, and steel mills.

Bamenda City, Cameroon 132 µg/m3 PM 2.5

Bamenda is a city in the northwestern mountainous region of Cameroon, and the only place in Africa to appear on this list. The air pollution is caused by rapid urbanization, leading to soil erosion.

Xingtai City, Hebei Province, China 128 µg/m3 PM 2.5

Xingtai City in Hebei Province, China, is the most air-polluted city in the country due to pollution from coal-fired power plants.

Delhi, India 122 µg/m3 PM 2.5

Delhi, India, once topped the list for pollution levels, but has dropped out of the top 10 thanks to a decrease in PM 2.5 levels. Statistics show that the pollution is primarily caused by motor vehicles and factories.

According to Dan Tri