Regardless of the reasons for any observed change, investigating
the short-term mortality effect of PM10 over time could provide
important information that may help quantify, the potentially
changing, health burden of exposure to ambient PM10. For example,
quantifying the current health burden of PM10 using a single effect
estimate based on, say, the previous 10 years of data would be
inappropriate if the adverse health effect of PM10 had been
declining over this period; The single effect estimate, based on the
previous 10 years of data, would overestimate the present day effect
of PM10, resulting in a commensurate over-statement of the
current public health burden of PM10.