According to WHO data, more than seven million people die every year from exposure to polluted air. That’s around one in every nine deaths on the planet.

The most polluted city in India & the world is Zabol in Iran, according to WHO figures. The city’s air quality is so bad that it can lead to serious health conditions like lung cancer and chronic obstructive pulmonary disease (COPD).

The second and third most polluted cities are Gwalior and Allahabad in India. They have high levels of particulate matter – tiny particles which float in the air – which can cause asthma or lung cancer if inhaled over a long period of time.

In fourth place is Ulaanbaatar, Mongolia’s capital city where winter temperatures often fall below minus 30 degrees Celsius (-22 Fahrenheit). It has high levels of nitrogen dioxide (NO2), a gas produced by burning fossil fuels

1. Delhi, India

The second-most populated city in the world is also one of its most polluted.

Delhi has the eighth-highest levels of air pollution among all cities, and is the world’s second-noisiest city. It’s also home to more than 20 million people – making it one of the most densely populated cities in the world.

The city has been named as one of the most dangerous for children by UNICEF, with breathing problems being common among those living here. And it’s not just bad for humans – Delhi’s air has also been linked with an increase in heart disease mortality rates, chronic obstructive pulmonary disease mortality rates and low birth weight babies.

2. Peshawar, Pakistan

If you’re travelling to Pakistan, then chances are you’ve heard about the country’s notorious pollution problem. But even if you haven’t planned a trip there just yet, it’s important to know where exactly on the map you should avoid.

In a recent report by WHO, Peshawar was named as the sixth most polluted city in the world. It’s only the sixth-biggest city in Pakistan, but Peshawar’s air quality levels set it apart. The city’s PM2.5* level is 10 times over WHO’s air quality guidelines, while the concentration of PM10 in the air takes the cake, at 26 times over the guideline. That means that if you took Peshawar’s excess PM10 level and shared it among 26 other cities, you’d meet the guideline.

Many vehicles in the city run on diesel or an inferior quality fuel, resulting in worse emissions than necessary, but the main issue is Peshawar’s 450 brick kilns. These kilns produce massive amounts of pollution, not least by burning fuels like rubber, which leads to losses in productivity.

3. Kanpur, India

In the industrial hub of Uttar Pradesh – India’s most populated state – too many industries in the city burn coal, and too many citizens use harmful biomass boilers. Vehicles in Kanpur pump emissions into the air on a daily basis while driving on mostly unpaved roads, and local leather tanneries release dangerous emissions.

Professor Sachchida Nand Tripathi, who heads up the Indian Institute of Technology Kanpur’s civil engineering department, told Reuters: “The state government does not have the mechanism to understand the sources of air pollution, how will they tackle it?”

The professor added: “The state needs to act. This was very much coming.”

4. Rawalpindi, Pakistan

Pakistan’s second city of Rawalpindi has been named as having one of the worst air quality in the world by IQAir.

The industrial city has been ranked at number three in the list of 20 most polluted cities, with a PM2.5 concentration of 250 micrograms per cubic meter (mg/m3). The WHO recommends that countries aim to keep their PM2.5 readings below 25 mg/m3.

Rawalpindi is followed by Karachi and Lahore, which both have an annual average PM2.5 reading of 200 mg/m3.

IQAir’s study looked at data from more than 1,500 cities across 91 countries around the world, taking into account factors such as air pollution levels, population density, and number of vehicles on the road

According to IQAir’s data, 22% of all deaths in Pakistan are due to pollution, and Rawalpindi is the second-biggest offender after Karachi. You can find steel-rolling mills, leather tanneries, marble factories, oil refineries, and brick kilns – all discharging dangerous emissions into the air – but very few green areas.

5. Faridabad, India

The city of Faridabad is located in the northern Indian state of Haryana. It’s a hub for manufacturing and commerce, so it’s no surprise that it regularly tops the list of India’s most polluted cities.

Faridabad is famous in India for producing and exporting henna, a dye created using plant material that’s used for temporary body art and to change people’s hair colour. As well as the emissions that come from making henna, the city also releases harmful gases while producing air conditioners, clothes, motorbikes, fridges, shoes, switch gears, syringes, tractors, tyres and more.

Like many cities on this list, Faridabad’s streets are full of old vehicles – many of which run on diesel and have to navigate around construction sites and roadworks – which also send particulate matter of all sizes into the air. Refuse is burned in the open along with rubber and plastic; this produces dark plumes of deadly smoke.