Concerning APOE genotype, 1 μg/m3 increase of PM2.5 was associated with a 78% (1.53–2.0) higher hazard for dementia in APOEε4 noncarriers and an 83% (1.48–2.26) increased hazard in ε4 carriers, while a 10 μg/m3 increase of NOx was linked with a 3% increased dementia risk both in noncarriers (1.02–1.04) and carriers (1.01–1.05). This evidence concerns the gene APOE and dementia.