Is Association between Mortality and Air Pollution due to a Short Temporal Displacement?

Standard methodology for analysis of air pollution epidemiological time series expresses effects in terms of relative risk, i.e. increases in the number of events associated with a short term increase in air pollution. However, even large relative mortality rates may in fact reflect a very small effect in terms of person-years life loss. In Zagreb, mortality in 1995–1997 was significantly associated with concentrations of nitrogen dioxide NO2 . We have used STL decomposition of time series into additive components of decreasing smoothness to test the hypothesis that mortality — air pollution association is due to short term mortality displacement. According to our results association between mortality and concentrations of NO2 remains statistically significant at time scales ranging from a few days to 1–2 months.