Smoke rises form brick kilns in Peshawar. PHOTO: AFP

Of the Pakistani cities, Karachi, Peshawar and Rawalpindi are among the 20 most polluted cities in the world, as per the most recent statistics from the World Health Organisation (WHO) compiled from more than 1,600 cities for the years 2008 to 2013.Karachi ranks number five just ahead of Peshawar and Rawalpindi which stand at six and seven in the list of 20 most polluted cities.The WHO report listed 1,600 cities in 91 countries and ranked them according to the quality of their air which is measured for concentrations of PM10 and PM2.5 that is particles smaller than 10 or 2.5 microns which are harmful toxins that can cling to the lungs and cause diseases.Pakistan records the highest level over all of the 91 countries in the WHO air pollution database.Interestingly, 13 of the 20 cities on the list are Indian. Delhi tops the list of the most polluted cities followed by Patna, Gwalior and Raipur.The report is a cause of serious health concerns for the inhabitants of the respective cities as toxic pollution hugely impacts human health and can cause acids rains, heart disease and respiratory problems among others.Pakistan, India and China are also polluted in terms of particulate matter. The WHO examined the concentration of the fine particles and advised that fine particles of less than 2.5 micrometres in diameter (PM2.5) should not exceed 10 micrograms per cubic metre.