The usual approach of epidemiological studies is to measure the association between at least one specific pollutant (. PM, NOx, CO or O3) and health outcomes. These specific components are usually highly correlated with other pollutants and are considered indicative of the complex pollutant mixture. It is unclear how much the associations reported in epidemiological studies represent the independent effects of specific pollutants. This correlation means that simply summing the pollutant-specific impacts could lead to an overestimation of the overall impact of air pollution on health. Because of the potential to overestimate the impact of air pollution on health,.
