AbstractObjectiveAlthough chronic exposure to air pollution is associated with an increased risk of dementia in normal elderlies, the effect of chronic exposure to air pollution on the rates of cognitive decline in Alzheimer's disease (AD) has not been elucidated.MethodsIn this longitudinal study, a total of 269 patients with mild cognitive impairment or early dementia due to AD with the evidence of brain β‐amyloid deposition were followed‐up for a mean period of 4 years. Five‐year normalized hourly cumulative exposure value of each air pollutant, such as carbon monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2), and particulate matter (PM2.5and PM10), was computed based on nationwide air pollution database. The effects of chronic exposure to air pollution on longitudinal cognitive decline rate were evaluated using linear mixed models.ResultsHigher chronic exposure to SO2was associated with a faster decline in memory score, whereas chronic exposure to CO, NO2, and PM10were not associated with the rate of cognitive decline. Higher chronic exposure to PM2.5was associated with a faster decline in visuospatial score in apolipoprotein E ε4 carriers. These effects remained significant even after adjusting for potential confounders.InterpretationOur findings suggest that chronic exposure to SO2and PM2.5is associated with faster clinical progression in AD.