As stated in preamble to the 1997 PM National Ambient Air Quality Standards (40 CFR 50, 1997), the consistency of the results of the epidemiological studies from a large number of different locations and the coherent nature of the observed effects are suggestive of a likely causal role of ambient PM in contributing to the reported effects, which include premature mortality.
Ambient PM may have contributed to premature mortality.
Ambient PM was not found to be a contributing factor.