Interaction of evolutionary ages (Mya) with air pollutant exposures in determining repetitive element DNA methylation. Effects on DNA methylation estimated by modeling interactions of metal-rich PM10 exposure with ages of LINE-1 subfamilies in Study 1 (panel A); interactions of metal-rich PM10 exposure with ages of Alu subfamilies in Study 1 (panel B); interactions of airborne benzene exposure with ages of LINE-1 subfamilies in Study 2 (panel C). The differences in DNA methylation in each subfamily are represented using τ. The evolutionary ages shown are arbitrary numbers at regular intervals of 2, 6, 11, 15, and 20 million years ago (Mya), reflecting a plausible range and spaced intervals of evolutionary ages. The interaction p-values are shown in the figures.