According to the World Health Organization, the air in these 30 cities was found to be the most polluted in 2016. The air in these cities contains high levels of dangerous particulate matter, small enough to enter the human bloodstream through the lungs—a problem that contributes to an estimated 7 million premature deaths each year.

We’ve ranked the cities here, from least to most polluted.

The old Blue City of Jodhpur is a popular tourist destination. But a lack of rain contributes to its poor air quality.

Steel mills, like the one seen in this picture, are a leading contributor to particulate matter in the air in China’s Hebei province.

Ugandan military police patrol a street in Kampala in 2016. Pollution researchers have cited vehicle emissions as a leading cause of air pollution in Kampala.

Pollution haze is visible in this photo of the Taj Mahal. The particulate matter in Agra is caused primarily by the practice of burning of scrap tires to extract iron.

There is a large nuclear power plant in Bushehr, but frequent dust storms and vehicle emissions are to blame for the dense, polluted air.

These Bangladeshi travelers are seen crossing the Shitalakhya River. The banks in the distance are obscured by pollution from the bustling brick-manufacturing industry.

This chemical factory in Hengshui might feed Hebei province’s booming economy, but it also contributes to the region’s dangerous levels of air pollution.

This area of Pakistan is home to steel rolling mills, leather tanning facilities, marble factories and oil refineries. All of these industries can, under certain conditions, negatively impact air quality. In this picture, a laborer is seen working at a brick kiln.

The steel industry is the primary culprit behind the air pollution in this city in the Indian state of Punjab, according to its own state government.

Tourists and Sikh devotees visit the Golden Temple by the hundreds of thousands each day. This Sikh man swims in the holy sarovar with the temple in the distance, shrouded in smog.

This picture shows another black cloud rising from a brick factory.

These workers are testing a dust-suppression truck. This water cannon purports to suppress smog and promote clear, healthy air.

In response to growing pollution from vehicle emissions, Lucknow built a metro rail service. This photo shows the fanfare of the train’s inaugural run.

Just on the other side of the Yamuna River from Agra and the Taj Mahal, Firozabad has a booming glass industry. The glass-making factories have earned the city the nickname City of Bangle, but the industry isn’t great for the air quality. 

In the Indian state of Punjab, a farmer naps in a wheat storage facility. Vehicle exhaust, industrial emissions and agricultural pollutants all contribute to the poor air quality in Khanna.

In this photo, workers pile buffalo hides to be made into leather at a tannery in Kanpur. Leather tanneries can release dangerous chromium into the air.

Some schools have snow days, but schools in Shijiazhuang have the occasional smog day.

As recently as the 1940s and 50s, Dammam was a quiet fishing village, but the discovery of oil transformed this area into a hub for the Saudi energy industry.

This photo shows a person performing the Sikh martial art Gatka in a sports festival in the southern outskirts of Ludhiana. Coal-burning power plants in the area turn the air a misty grey color.

The Indian capital was once the most polluted city in the world. The city still struggles with pollution from the burning of nearby rice paddies, burning municipal waste, and vehicle exhaust emissions.

Chimneys cloud the skyline of Baoding. Coal is used to power the city and the surrounding villages.

The industrial steel city of Xingtai ranks as China’s most polluted.

Unlike many of the world’s most polluted cities, deforestation and changing weather patterns are the primary explanation for the city’s poor air quality.

This area is plagued by pollution from sponge iron factories; the process of producing sponge iron can be particularly dirty due to the low quality of certain raw materials.  In this photo, activists in Raipur are seen protesting the deaths of 13 women who were sterilized in a government-run medical program. 

Hindu devotees return from a ceremony during Chhath Puja, a fall Hindu festival thanking the Sun God for sustaining life on earth. Thick smog obscures the sunset.

This billboard at the Maaden Aluminium Factory advertises the third-largest producer of aluminum in the world. The industry is also the culprit behind the severely polluted air in Al Jubail.

The Saudi capital experiences severe sandstorms on top of the emissions from vehicles and industrial factories. The tiny sand particles are dangerous to inhale.

The residents of Allahabad deal with the perfect storm of pollution. Changing wind patterns, coal-burning power plants, vehicular emissions, and deforestation all leave this city, quite literally, in the dust.

An Indian woman sits in a hospital corridor with her child. Outside, in India’s most polluted city, particulate matter from burning garbage and fossil fuels makes the air hazardous to breathe.