to investigate the possible relationship between airborne particulate matter and mortality , we developed regression models of daily mortality counts using meteorological covariates and measures of outdoor pm10 . 
 our analyses included data from cook county , illinois , and salt lake county , utah . 
 we found no evidence that particulate matter < or = 10 microns ( pm10 ) contributes to excess mortality in salt lake county , utah . in cook county , illinois , we found evidence of a positive pm10 effect in spring and autumn , but not in winter and summer . 
 we conclude that the reported effects of particulates on mortality are unconfirmed.imagesfigure 1 . 
 afigure 1 . 
 bfigure 2 . 
 afigure 2 . 
 bfigure 2 . 
 cfigure 2 . 
 dfigure 2 . 
 efigure 2 . 
 ffigure 3 . 
 afigure 3 . 
 b