Cities in Iran, India, Pakistan and the capital of Mongolia rank among the worst on the planet for air pollution, while those in the US and Canada are among the best, according to the first global survey, released Monday by the World Health Organization. The southwest Iranian city of Ahvaz walked away with the unfortunate distinction of having the highest measured level of airborne particles smaller than 10 micrometers. WHO released the list to highlight the need to reduce outdoor air pollution, which is estimated to cause 1.34 million premature deaths each year. The global body said investments to lower pollution levels quickly pay off due to lower disease rates and, therefore, lower healthcare costs. The list, which relies on country-reported data over the past several years, measures the levels of airborne particles smaller than 10 micrometers — so-called PM10s — for almost 1,100 cities. WHO recommends an upper limit of 20 micrograms for PM10s, which can cause serious respiratory problems in humans. They are mostly sulfur dioxide and nitrogen dioxide from power plants, auto exhausts and industry. Ahvaz's annual average of PM10s was 372 micrograms per cubic meter.
