The objectives of this study conducted in the Nantes metropolitan area are to: - comply with the regulatory requirement of the Regional Air Quality Plan to assess the health effects of air pollution; - provide the public with information on the local impact of air pollution on health. The purpose of this study is therefore to calculate the short-term health impact under various pollution scenarios (shifts from an average level to a higher or lower level), using the following indicators: - all-cause mortality; - hospital admissions for respiratory and cardiovascular causes. The study focuses on the Nantes metropolitan area because the prevalence of exposure is higher there (larger population and greater pollution) than in other areas of the region. Furthermore, for several years now, the area has had data on population exposure to air pollution thanks to an air quality monitoring network (Loirestu'air, a non-profit association founded in 1980). This document presents the entire health impact assessment (HIA) process implemented in the Nantes metropolitan area. (R.A.)