Quantifying the health impacts of outdoor air pollution: useful estimations for public health action.

The typical procedural steps in HIA include screening, scoping, assessment of health effects, recommending alternatives and mitigations, reporting and monitoring. Each step helps predict or foresee potential effects of policy decisions on a population's health. In specific, quantitative risk assessment, an essential component of HIA, provides estimations of the potential health risks or impacts associated with a variety of hazards. Since the beginning of HIA development, environmental risk factors have been one of the targeted groups of health determinants —besides the social ones. In this commentary, we would like to discuss some methodological aspects and potential uses of the quantitative estimation of the health impact of outdoor air pollution. In recent years, this hazard has been one of the environmental factors most frequently quantified using HIA because the toxicological and epidemiological evidence supports a strong causal relationship between exposure and health effects. Since the individual risk from air pollution is relatively low while the whole population is exposed, HIA provides a clearer view of its impact on public health. The classical HIA method, derived from the WHO-HIA general method, quantifies the impact on health of short-term and long-term exposures to air pollution using four successive steps: (1) selecting concentration-response functions (ie, relative risks, (RRs)) from epidemiological studies; (2) estimating the distribution of exposure levels in the population studied; (3) collecting data on the prevalence or incidence of selected health indicators and, finally, (4) calculating the number of attributable cases. In the following, we discuss the different ways of formulating these HIAs and their implications for health and economic valuation. We then briefly review the uncertainties in HIA calculations and discuss the usefulness for different groups of quantitative estimations from HIAs. Lastly, we address recent advances and future use of the quantitative component of HIAs. In boxes, we illustrate how HIA quantification was performed in two projects on air pollution and health in Europe.