pollutant : particulates ,  including black smoke ( mainly fine carbon particles ) , dust soot ( coarse carbon particles ) .

Source:  They are produced by refuse incineration , factories , diesel vehicles , construction sites , and coal/charcoal burners .

Hazardous to health:  Very fine particulates ( diameter less than about 1um ) are most hazardous . They are not filtered out by hairs and mucus in the nose but are drawn deep to the lungs , where they can remain indefinitely and impair lung function by constricting respiratory passage and damage lung tissue , and cause respiratory illness . Certain particles are suspected to cause cancer .