World Health Organization Ranks Cities By Air Quality

A survey released by the World Health Organization on Monday has ranked the world’s cities according to air quality. Cities in the Middle East and Asia ranked among the most polluted cities, while cities in the U.S. and Canada ranked among the least polluted.

The WHO conducted the study measuring air quality to bring attention to the problem of air pollution, which poses risks to human health. Every year, 1.34 million people die prematurely from causes related to poor air quality. On its website, the WHO notes that acute diseases, such as pneumonia, can be caused by air pollution, as well as chronic diseases such as lung cancer. Children and the elderly are particularly at risk, as are those with limited access to quality health care.

The list, which includes information for almost 1,100 cities in 91 countries, was compiled using country-reported data about air quality from between 2003 and 2010, with most of the data coming from 2008 and 2009. Data was taken from sources including publicly available websites, regional networks, reports, and other publications.

To assess the air quality of a city, the WHO measured the levels of airborne particles smaller than 10 micrometers, which are also known as PM10s. PM10s are made up of mostly nitrogen dioxide and sulfur dioxide, which are released from car exhaust and power plants. PM10s pose a risk to respiratory health in humans; to lower the risk of health problems, the WHO recommends an upper limit of 20 micrograms per cubic meter.

Ahvaz, a city in southwestern Iran, has been given the title of the world’s most air polluted city. With a population of 1.3 million, Ahvaz has an annual PM10s average of 372 micrograms per cubic meter. The study notes that low-quality vehicle fuel and heavy industry practices in the area are the main causes for the poor air quality in the city.

Second on the list of the world’s most polluted cities was the Mongolian capital of Ulan Bator, which has an annual PM10s average of 279 micrograms per cubic meter. Sanandaj, another city in western Iran, came in third with an annual PM10s average of 254 micrograms per cubic meter. Cities in India, Pakistan, and Botswana also ranked high on the list.

The problem of poor air quality has long been an issue in Asia. Contributing factors include lack of public transportation, high population densities, and lax regulations on air quality control. The WHO also notes that rapid industrialization and low-quality fuels used for cars and electricity are major components of the poor air quality.

To combat the problem of poor air quality, steps are being taken in polluted countries such as India. Large cities like Mumbai, New Delhi, and Kolkata have ordered that no more power plants can be constructed within the city limits; existing power plants are either being shut down or relocated. At the same time, however, a lack of efficient public transportation in these cities has caused a huge surge in ownership of private cars and SUVs. This poses its own set of problems, as these cars are major contributing factors to poor air quality.

The study also ranked cities with the best air quality. Cities in Canada and the U.S. ranked highly, due to the lower population density, climate, and strict regulations on air pollution. Whitehorse, the capital of Yukon territory, had an annual PM10s average of only 3 micrograms per cubic meter. Second on the list was Santa Fe, New Mexico, with an annual PM10s average of 6 micrograms per cubic meter. Washington D.C., Tokyo, and Paris were also given the distinction of having good air quality.

In addition to the data compiled about the presence of PM10s, the WHO also released a shorter list that examined the levels of PM2.5s, which are even finer dust particles in the air. Harmful levels of PM2.5s are 10 micrograms per cubic meter.

Photo Credit: niehs.nih.gov/health/assets/images/smoke_billowing_from_the_smoke_stacks.jpg

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