Scientists have revealed which are the most polluted cities in the world where their inhabitants are most at risk of inhaling toxic particles.
Topping the 100-person list is the Vietnamese capital Hanoi, the only city with a level of air pollution described as “very unhealthy.”
In the densely populated capital, levels of a major 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.
Only two British cities are on the list: Birmingham, which is ranked 57th, and London, which is ranked 89th.
Hanoi in Vietnam is the most polluted city in the world, followed by Tehran in Iran, Bishkek in Kyrgyzstan and Kolkata in India.
He classification has been provided by IQAir, a Swiss air quality technology company specializing in protection against airborne contaminants.
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 classification can highlight the impact of events such as wildfires, biomass burning, industrial activity, sandstorms and reverse weather events on air quality in a city,” IQAir said in a statement.
According to the company, Hanoi is plagued by a pollutant known as PM2.5: small 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 through the lungs.
In Hanoi, the concentration of PM2.5 is no less than 41.8 times the annual air quality guideline given by the World Health Organization (WHO), IQAir said.
Hanoi topped air monitoring website IQAir’s chart of the world’s most polluted cities, with the level of air pollution described as “very unhealthy”.
Hanoi has frequently been among the most polluted cities in the world, due in part to widespread construction and emissions from the large number of motorcycles and cars that criss-cross the capital every day.
But other serious air pollution in the city includes nitrogen dioxide (NO2), a reactive gas formed by motor vehicle emissions that irritates the airways.
Outside, NO2 contributes to the formation of ozone (O3), the main ingredient in smog, which is also linked to health problems such as chest pain, bronchitis and asthma.
In recent years, Hanoi has frequently been among the world’s most polluted cities, due in part to widespread construction and emissions from the large number of motorcycles and cars that crisscross the capital every day.
Carbon emissions from northern coal plants and agricultural burning exacerbate the problem.
“I have had to wear a mask every time I went out in recent 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’ve had to limit my time outdoors,” Huong told AFP.
In total, 19 of the 20 most polluted cities are in Asia (with the exception of Mexico City), which experts describe as “not surprising.”
“Unfortunately, this is not at all surprising and is supported by a lot of evidence, such as 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 ranked number 3 on the list. In the photo, Victory Square near the Kyrgyz Mountain Range, Bishkek.
Beijing, China (pictured) is currently ranked 9th, just ahead of Wuhan (10th) on IQAir’s list. Both cities have air pollution classified as “unhealthy”
“This is mainly due to a combination of very limited air pollution regulations, the use of outdated equipment with insufficient air pollution mitigation, and high population density.”
Professor Alastair Lewis, of the National Center for Atmospheric Sciences at the University of York, agreed, saying he was “not particularly surprised”.
“Other factors that can affect places in Asia are the burning of crop residue – this can have a huge impact on cities like Delhi,” he told MailOnline.
‘There are also natural fires and many countries with a high level of pollution are all very close to each other.
“And of course, in Hanoi itself the transport fleet – cars, buses and trucks – may include some very old vehicles with poor or possibly no emissions control.”
However, Professor Lewis also said he was surprised to see Birmingham as the highest city in the UK.
Pictured is the skyline of Tehran in Iran with skyscrapers, pollution and snow-capped Alborz Mountains in the background. Air pollution in Tehran described as “unhealthy”
“This is likely to be affected by some specific weather conditions, as central London is overall the most polluted city in the UK, although much cleaner than many cities higher up the list,” he told MailOnline.
The IQAir rating is updated at least once an hour as new air quality monitoring station data becomes available, meaning this current rating is a snapshot.
However, cities in the top 20 at any given time do not move up or down the list significantly, and Hanoi sits firmly at the top.
“This ranking order is likely to change from day to day depending on the weather, which is an important factor that can worsen air quality if wind speeds are low,” Professor Lewis added.