“Epidemiologists are a little bit challenged to try and sort out when we find these associations — is it because of these other pollutants or is it because of nitrogen dioxide?” said Jon Samet, an epidemiologist with the Colorado School of Public Health. But Samet argues that just because there are other sources of NO2 doesn’t mean gas stoves are a nonissue. These factors make it all the more challenging to isolate the gas stove’s role.