Scientists have identified the world’s most polluted cities, whose residents are most at risk of inhaling toxic particles.
At the top of the 100-strong list is the Vietnamese capital Hanoi, the only city with air pollution levels described as “very unhealthy”.
In the densely populated capital, levels of a key pollutant linked to heart disease, asthma and even cancer are 40 times higher than recommended guidelines.
Other cities in the top 20 include Istanbul in Turkey, Delhi in India, Beijing and Wuhan, both in China, and Dubai in the United Arab Emirates.
There are only two British cities on the list: Birmingham at number 57 and London at number 89.
Hanoi in Vietnam is the most polluted city in the world, followed by Tehran in Iran, Bishkek in Kyrgyzstan and Kolkata in India
The ranking was provided by IQAir, a Swiss air quality technology company specializing in protection against air pollutants.
It is based on data from thousands of air quality monitoring stations and air quality sensors operated by government agencies, research institutions and more.
“The immediacy of the ranking is able to highlight the impact of events such as wildfires, biomass burning, industrial activities, sandstorms and inversion weather events on air quality in a city,” IQAir said in a statement.
According to the company, Hanoi is plagued by a pollutant called PM2.5 – tiny particles or droplets less than 2.5 micrometers in diameter that are invisible to the naked eye and are inhaled without even realizing it.
Research has shown that these cancer-causing microparticles are small enough to enter the bloodstream via the lungs.
In Hanoi, PM2.5 levels are a whopping 41.8 times the World Health Organization’s (WHO) annual air quality guideline, IQAir said.
Hanoi tops air monitoring website IQAir’s table of the world’s most polluted cities, with air pollution levels described as “very unhealthy”.
Hanoi is often ranked among the world’s most polluted cities, due in part to widespread construction and emissions from the large number of motorcycles and cars that pass through the capital daily
Another serious air pollution in the city is nitrogen dioxide (NO2), a reactive gas produced by motor vehicle exhaust that is a respiratory irritant.
Outdoors, NO2 contributes to the formation of ozone (O3), the main component of smog, which is also linked to health problems such as chest pain, bronchitis and asthma.
In recent years, Hanoi has often been ranked among the world’s most polluted cities, due in part to widespread construction and emissions from the large number of motorcycles and cars that pass through the capital daily.
Carbon emissions from coal-fired power plants in the north and agricultural combustion are exacerbating the problem.
“I had to wear a mask whenever I went outside in the last few days because the air quality was so bad,” said office worker Nguyen Minh Huong.
“It’s hard to breathe. “I sneeze all the time, so I had to limit my time outside,” Huong told AFP.
Overall, 19 of the 20 most polluted cities are in Asia (excluding Mexico City), which experts say is “not surprising.”
“This is unfortunately completely surprising and is supported by a lot of evidence, including surface measurements, satellite data and models,” Philip Stier, professor of atmospheric physics at the University of Oxford, told MailOnline.
Bishkek, the capital of Kyrgyzstan, is currently at number 3 on the list. Pictured: Victory Square near the Kyrgyz Mountains, Bishkek
Beijing, China (pictured) is currently ranked 9th, just ahead of Wuhan (10th) on IQAir’s list. In both cities, air pollution is described as “unhealthy”.
“This is primarily due to a combination of very limited air pollution regulations, the use of outdated equipment with inadequate air pollution control, and high population density.”
Professor Alastair Lewis, from the University of York’s National Center for Atmospheric Science, agreed and said he was “not particularly surprised”.
“Other factors that can impact places in Asia include the burning of crop waste – this can have a huge impact on cities like Delhi,” he told MailOnline.
“There are also natural fires and many countries with high levels of pollution are all in close proximity to each other.”
“And of course in Hanoi itself the transport fleet – cars, buses, trucks – may include some very old vehicles with poor or possibly no emissions controls.”
However, Professor Lewis also said he was surprised to see Birmingham as the highest city in Britain.
Pictured is the skyline of Tehran, Iran with skyscrapers, pollution and snow-capped Alborz mountains in the background. Air pollution in Tehran is described as “unhealthy”.
“This is likely to be influenced by certain weather conditions, as central London is generally the most polluted city in the UK, although it is much cleaner than many cities higher up the list,” he told MailOnline.
IQAir’s rankings are updated at least once an hour as new data from air quality monitoring stations becomes available. Therefore, this current ranking is a snapshot.
However, at no point do the cities in the top 20 move up and down significantly – and Hanoi is firmly at the top.
“This ranking is likely to change from day to day depending on the weather, which is an important factor that can worsen air quality when wind speeds are low,” Professor Lewis added.
