The World Health Organization (WHO) set the air quality guideline for cities around the globe. This air quality guideline is an annual mean concentration guideline for particulate matter. Particulates are measures in PM2.5 and PM10, which is in relation to the size of the particles in the air. PM10 means the particles are smaller than approximately 10 micrometres. This size particle can settle in the lungs and can cause serious health problems. PM2.5 is the measurement of particles under 2.5 micrometres. This size particle is particularly harmful to humans; a study showed that as the amount of PM2.5 increase, so do the instances of lung cancer, up to a 22 percent increase.
The guidelines set by the World Health Organization stipulates that PM2.5 should not exceed 10 micrograms per cubic meter as an annual mean, or 25 micrograms per cubic meter in a 24-hour means. For PM10, measurements should not exceed 20 micrograms per meter cubed annually and 50 micrograms per cubic meter in a 24-hour mean. Despite these World Health Organization guidelines, hundreds of cities around the world are falling short by a huge margin. The worst city in the world was Zabol in Iran, which has an annual PM2.5 of 217 and an annual PM10 of 527. Checking this against the WHO’s guideline shows air pollution in Zabol is more than 21 times the recommended limit for PM2.5 and more than 26 times the recommended limit for PM10.
Zabol is the capital of Zabol County, Sistan and Baluchistan Province in Iran and lies on the border of Afghanistan with a population of around 130,000. The area around Zabol is known for its “120-day wind” which originates in the deserts and blows hot sand and dust for large parts of the year. The air pollution is that bad in Zabol that a 2017 study by the Preventive Medicine journal suggested that cycling outdoors in Zabol’s poor air for 30-minutes would cause that much harm that it would outweigh the health benefits of the exercise.
Cities from India make up four of the current top 10 polluted cities in the world. Gwalior is second on the list with annual mean PM2.5 of 176 and PM10 of 329, with Allahabad coming in at number three with a PM2.5 of 170 and a PM10 of 317. Both of these cities have populations in excess of one million, which is quite worrying seeing how the air they breathe on a daily basis is so poor it has been likened to smoking up to 50 cigarettes when air pollution it at its peak. The other Indian cities to make the unwanted top 10 are Patna and Raipur, while Delhi and Ludhiana, Kanpur, Khanna, Firozabad and Lucknow are all part of the top 20. Occupying the fourth and fifth spot in the most polluted cities in the world are in Saudi Arabia. Riyadh is number four with the industrial city of Al Jubail being number five. Both cities have higher PM10 levels than all but a couple of the worst 500 cities. Bamenda in Cameroon is the worst polluted city in Africa according to PM2.5 particulate matter. Its levels of 132 place it eighth in the world.
There is a pattern when it comes to ranking the countries with the most polluted urban areas Pakistan is the worst with an average PM2.5 concentration of 115.7 followed by Qatar (92.4), Afghanistan (86), Bangladesh (83.3), Egypt (73), UAE (64), Mongolia (61.8), India (60.6), Bahrain (56.1) and Nepal (50). All would be considered to be developing or third-world countries in hot, desert areas. Sadly, all people living in these countries are having years taken off their lives due to the air they are forced to breathe.