studies were performed to compare the physical and chemical characteristics and the in vitro macrophage cytotoxicity of oil and coal fly ash . 
 sampling methodology was developed to collect size - fractionated particulate matter from the smokestack of either a coal - fired or an oil - fired power plant . 
 morphological studies demonstrated particle heterogeneity , although most coal fly ash particles appeared to be spherical . 
 oil fly ash contained two major morphologies ; nonopaque amorphous particles and opaque amorphous particles . 
 elemental analysis indicates that the coal ash is predominantly composed of aluminosilicate particles , while the oil ash is predominantly inorganic sulfates and carbonaceous particles . in vitro macrophage assays 
 demonstrate that the finest coal fly ash particles are the most cytotoxic ; the cytotoxicity is significantly less than that of alpha - quartz , the positive control particle . 
 in contrast , the oil fly ash particles are more cytotoxic than quartz . 
 the cytotoxicity of oil fly ash is due to soluble components , possibly vanadium salts.imagesfigure 2 . 
 afigure 2 . 
 bfigure 2 . 
 cfigure 2 . 
 d