When George Thurston leaves his cottage in the woods of Waccabuc, N.Y., to head for work, a pollution monitor clipped to his belt—called an AirBeam —shows pristine air quality. As he takes the train through the suburbs, the device’s digits rise, meaning more pollution. By the time he gets to his office in Manhattan, they’re even higher. “It’s important to know your exposure profile to protect against everyday cumulative risk,” says Thurston, professor of medicine and population health at NYU’s