I fail to understand how a reputed organization such as the WHO has made such a comparison and issued this report. Both geographically and climatically, it is just not possible to compare any Middle East or Asian city to any of the cities in the West. Canada, Finland, Iceland, the US, and Sweden remain covered with ice and snow for a major part of the year. Added to this are the rains they receive which cause the dust to stay settled down. Compared to the above countries, Doha is a desert country with hardly any rain. Most citizens of the above countries would hardly have the courage to venture out of their homes during the periods of sandstorms which Doha faces. Also, the above countries are larger area-wise and the population is spread over a wide area in several cities as compared to Doha where the major population is centered in just one city. As such, the report by the WHO singling out Doha as one of the twenty most polluted countries, leaves much to question on fairness of the experiment.
As for Asian countries, most of them are heavily populated compared to the western cities. Wherever there is a high concentration of population, there is bound to be pollution.