4 Epidemiologic evidence associates cognitive deficits with PM2.5 exposure among the elderly.5 Rodent models also show long-term neurotoxic effects of air pollutants, including memory impairment6 and selective atrophy of CA1 hippocampal neurons observed in pre-clinical AD;7 decreased glutamate receptor subunit GluR1;8 and increased endogenous soluble Aβ.9, 10, 11 However, we lack prospective studies of PM exposure on ADRD risk and interaction with APOE alleles. This evidence concerns the gene APOE and Alzheimer disease.