APOE and Cognitive impairment: 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.