What city? It is too generic to say "Southeast Asia". Most of it is rural. And what is meant by "unhealthy"? What measurements? I cannot believe that 90% of days were unhealthy. Why? Rainy season is never polluted -- I know from experience in Hongkong and Singapore. Once a day or more, you get a huge downpour that takes most pollution out of the air. (This is partly why Seattle fairs very well in clean air measurements... it rains so damn much. Scottish cities, too.)