Ulan Bator is not only one of the coldest capitals on earth, it's also a city with massive air pollution. During the winter months, yurts like Tsegi’s are heated with coal and wood which contributes up to 70 percent of the smog in the city. Air pollution in Ulan Bator is seven times higher than what is considered safe by the WHO.

The Chinese capital has been suffering from smog so heavy that scientists say the city is almost uninhabitable - although it is home to 20 million people. Models suggest that 3.5 million people die globally every year because of air pollution - almost half of them in China. Having said this, it might be a surprise to learn that smog is an even bigger problem in other cities across the world.

Air pollution is one of Pakistan's main environmental concerns. The situation is particularly dramatic in the country's second largest city, Lahore. The smog is caused primarily by the high volume of road traffic, rubbish incineration and dust from the surrounding deserts.

In the nearly 10 million-strong city of New Delhi, the number of cars has increased from 180,000 to 3.5 million in the last 30 years. Still, it's the city's coal powered plants that are causing the biggest problem. They contribute to around 80 percent of the total air pollution in the city.

Sandstorms, like here in Riyadh, can contribute to smog forming because they increase the amount of particles in the air. In a place like Saudi Arabia, the intense ultra-violet rays also transform transport and industry emissions into ozone.

The poor air quality in Cairo causes a number illnesses among city residents, like chronic respiratory problems and lung cancer. The reason for the air pollution is an increase in road traffic and the booming industrial sector.

According to a study by the Max-Planck Institute in Mainz, some 15,000 people die every year in Dhaka due to air pollution. Researchers found the world's highest concentration of sulfur dioxide there.

Even if it looks the same the world over, smog is different, depending on the city. Smog in Moscow, for instance, is characterized by high amounts of hydrocarbons. The westerly winds which regularly plow across Moscow mean that the western part of the city generally has better air quality.

The smog in Mexico City is made worse by the geographical location. The city is surrounded on three sides by mountains. Due to the high levels of sulfur dioxide and hydrocarbons in the air, Mexico City was long considered one of the most polluted cities in the world. The situation is now improving due to new transport policies and certain factories being shut down.

Ulan Bator is not only one of the coldest capitals on earth, it's also a city with massive air pollution. During the winter months, yurts like Tsegi’s are heated with coal and wood which contributes up to 70 percent of the smog in the city. Air pollution in Ulan Bator is seven times higher than what is considered safe by the WHO.

The Chinese capital has been suffering from smog so heavy that scientists say the city is almost uninhabitable - although it is home to 20 million people. Models suggest that 3.5 million people die globally every year because of air pollution - almost half of them in China. Having said this, it might be a surprise to learn that smog is an even bigger problem in other cities across the world.

Air pollution is one of Pakistan's main environmental concerns. The situation is particularly dramatic in the country's second largest city, Lahore. The smog is caused primarily by the high volume of road traffic, rubbish incineration and dust from the surrounding deserts.

In the nearly 10 million-strong city of New Delhi, the number of cars has increased from 180,000 to 3.5 million in the last 30 years. Still, it's the city's coal powered plants that are causing the biggest problem. They contribute to around 80 percent of the total air pollution in the city.

Sandstorms, like here in Riyadh, can contribute to smog forming because they increase the amount of particles in the air. In a place like Saudi Arabia, the intense ultra-violet rays also transform transport and industry emissions into ozone.

The poor air quality in Cairo causes a number illnesses among city residents, like chronic respiratory problems and lung cancer. The reason for the air pollution is an increase in road traffic and the booming industrial sector.

According to a study by the Max-Planck Institute in Mainz, some 15,000 people die every year in Dhaka due to air pollution. Researchers found the world's highest concentration of sulfur dioxide there.

Even if it looks the same the world over, smog is different, depending on the city. Smog in Moscow, for instance, is characterized by high amounts of hydrocarbons. The westerly winds which regularly plow across Moscow mean that the western part of the city generally has better air quality.

The smog in Mexico City is made worse by the geographical location. The city is surrounded on three sides by mountains. Due to the high levels of sulfur dioxide and hydrocarbons in the air, Mexico City was long considered one of the most polluted cities in the world. The situation is now improving due to new transport policies and certain factories being shut down.