Estimating the public health burden attributable to air pollution: an illustration using the development of an alternative air quality index.

The example of the development of an alternative air quality index (AQI) is used to illustrate issues related to quantifying the public health burden attributable to air pollution. These issues include: (1) appropriately representing the weight of evidence; (2) extrapolation of risk measures over time and space; (3) attribution of health effects to air pollution versus other risk factors and to individual pollutants versus the rest of the mix; (4) application of complementary approaches from health economics; and (5) effective risk communication. A no-threshold, multipollutant AQI was developed, based on the relationship of CO, NO(2), O(3), SO(2) and PM(2.5) with mortality in Canadian cities in a daily time-series study. Risk coefficients were applied to daily air pollution concentrations to calculate multipollutant percent excess mortality, and results were scaled to a 0 to 10 range. The observed distribution of values was used to characterize days as low, medium, high, or extreme risk. Considerable day-to-day variability in the index value was observed, and the percent of days falling in the high or extreme risk categories ranged from 0.3 to 33.2 among the cities considered. The new index was moderately correlated with conventionally derived AQIs. Results did not appear to be sensitive to an alternative choice of risk coefficients based on a worldwide meta-analysis. Additional efforts will be required to validate this AQI formulation against one based on the association between air pollution and other health outcomes, and to most effectively utilize the AQI as a communication tool regarding acute health risks associated with air pollution.

Measuring progress in the management of ambient air quality: the case for population health.

Although progress has been made in the last few decades at reducing ambient concentrations of air pollutants, scientific evidence suggests that there remains a risk to human health from exposure to these pollutants at current levels in Canada. Much of the motivation for air pollution reduction efforts is to protect population health. This article presents a method of monitoring changes in air pollution-related health outcomes over time in conjunction with temporal changes in ambient pollution concentrations. The progress measure is a function of temporal changes in location-specific ambient concentrations and the potentially time-dependent association between those concentrations and daily deaths. The progress measure can be determined for a single location or at a national level. The measure can also be extended to include several pollutants. The progress measure is illustrated with an example of how changes in nitrogen dioxide levels in 12 Canadian cities from 1981 to 1999 have translated into changes in the percent of nonaccidental mortality burden attributable to this pollutant over time.