Motivated by the discussion above, in this paper we investigate
whether the short-term mortality effect of PM10 in three Australian
cities has changed during the period from the early to mid 1990’s to
2007. An observed decrease in the short-term mortality effect of
PM10 over time could, at least partially, be attributable to a decline
in the toxicity of PM10. However, it is important to note that an
observed decrease in the short-term mortality effect of PM10 over
time could be unrelated to the toxicity of PM10. Indeed, it is entirely
possible that the toxicity of PM10 did not change over the period of
investigation. There are many potential reasons for an observed
decrease in the short-term mortality effect of PM10 over time,
including: