Quantitative health impact assessment of outdoor air pollution in the Arve valley, France

Abstract

Introduction Health impacts of outdoor air pollution are a major concern in the Arve Valley located in the Alps. This valley is a mixed area, gathering 154,000 inhabitants in dense urban settings with a broad range of human activities, including tourisms and large natural spaces. The valley is surrounded by mountain massifs, and segmented by a series of bottlenecks that perturb air circulation. The valley is also the entry point of the tunnel under Mont Blanc with high levels of traffic. This topography, the concentrations of air pollutants sources in a restricted area, and the frequency of cold temperature inversions common in the valley during winter time, result in an exceeding of air quality target values for several pollutants. This situation has led some local stakeholders to claim that the valley was one of the most polluted areas in France and several non-governmental associations to ask for a better air quality. Method A quantitative health impact assessment (HIA) was conducted to help local stakeholders measure the expected benefits of improving air quality. It evaluated the effects of chronic exposure to fine particles (PM2.5) on mortality and life expectancy. Annual mean concentrations of fine particles from a fine-scale environmental model were coupled with land-occupancy data to estimate population exposure in 2007–2008 in the 41 municipalities affected by the atmospheric protection plan. The health benefits associated with several scenarios of improved air quality were computed based on a relative risk derived from European and French cohorts. Results The study shows that 8% of the mortality in the Arve Valley could be attributable to chronic exposure to PM2.5, representing 85 deaths per year. These results can be compared with the French nationwide estimate that on average PM2.5 contributed to 9% of the mortality, 8% in urban areas between 20,000 and 100,000 inhabitants, and 13% in urban areas larger than 100,000 inhabitants. A 30% reduction of average annual concentrations of PM2.5 would lead to a 4% decrease in mortality, representing 45 deaths avoided per year, and 967 life-years gained on average, or 5 months of life expectancy at 30 years. The qualitative analysis of uncertainties suggests an underestimation of health impacts, this quantitative HIA having provided a minimum scale of magnitude of the impact. The spatial and temporal heterogeneity of the exposition of the population in the Arve valley result in lower annual mean than in urban settings where concentrations are less influenced by meteorological conditions. This HIA does not take into account the wide range of possible health benefits in terms of avoided mortality and morbidity. Conclusions The study, based on an innovative method used for the first time in such an heterogeneous area, shows the large impact of outdoor air pollution on health in the Arve valley. This impact is similar to the one observed in French metropolitan areas between 20,000 and 100,000 inhabitants, without reaching the level found in the most polluted urban areas. In a context of acute debate, HIA is an efficient tool to provide comprehensive figures and to promote public interventions. Given the seasonality of the PM concentrations, actions should primarily target winter sources, especially residential wood-burning. Examples from the literature document that rapid and measurable health benefits were observed after interventions targeting biomass burning in similar context of residential wood-burning in valleys with common wintertime temperature inversions. Those long-term interventions should not prevent for immediate actions in case of acute episodes, involving the punctual reduction of some emissions sources, and information to protect the most vulnerable populations.