Temporal variation in association between short-term exposure to fine particulate matter and hospitalisations in older adults in the USA: a long-term time-series analysis of the US Medicare dataset.

Background: Short-term exposure to fine particulate matter (PM) is associated with increased risk of hospital admissions and mortality, and health risks differ by the chemical composition of PM. Policies to control PM could change its chemical composition and total mass concentration, leading to change in the subsequent health impact. However, there is little ence on whether associations between PM and health exhibit temporal variation.