A new report by the World Health Organization has warned that air pollution is worsening across much of the globe, with over 80 percent of the world's city dwellers breathing poor quality air, increasing the risk of lung cancer and other life-threatening diseases.
Urban residents in poor countries are by far the worst affected, the WHO said on Thursday, noting that only two percent of cities in low and middle-income countries had air which met the UN body's standards.
That number was 44 percent for cities in wealthier countries.
The WHO defines low-income economies as those with a gross national income (GNI) per capita of $1,045 or less, and high-income economies with a GNI per capita of more $12,736.
The report, which focused on outdoor rather than household air, compared data from 795 cities in 67 countries between 2008 and 2015.
Tracking the prevalence of harmful pollutants such as sulphate and black carbon, WHO found that air quality was worsening in developing regions, notably the Middle East and Southeast Asia but generally improving in richer regions like Europe and North America.
"Urban air pollution continues to rise at an alarming rate, wreaking havoc on human health," Maria Neira, the head of WHO's department of public health and environment, said in a statement.
"When air quality improves, global respiratory and cardiovascular-related illnesses decrease," she added.
Common causes of air pollution include too many cars, especially diesel-fuelled vehicles, the heating and cooling of big buildings, waste management, agriculture and the use of coal or diesel generators for power.
Overall, contaminants in outdoor air caused more than 3 million premature deaths a year, the UN body said.
India dominates list
Measuring the amount of particulates smaller than 2.5 micrometers (PM2.5), roughly 30 times smaller than the width of a human hair, the report found that India had 15 of the world's 30 most polluted cities.
The dirtiest air was recorded at Zabol in eastern Iran, which recorded a PM2.5 measurement of 217.
The city, which is located near the ancient site of Shahr-i Sokhta, a UNESCO World Heritage site, suffers from months of dust storms in the summer as temperatures soar above 40C.
The next four cities were Gwalior and Allahabad, in India, and Riyadh and Jubail, in Saudi Arabia.
India's capital, New Delhi, was the 11th worst city, with an annual average PM2.5 measurement of 122.
