A gas monitor apparatus includes a sorbent material that adsorbs a target gas based on a concentration of the target gas in a monitored environment and a reference material that does not respond to the target gas. The gas monitor also includes a first thermistor disposed within the sorbent material and a second thermistor disposed within the reference material, the first thermistor to provide a first indication of a first temperature of the sorbent material and the second thermistor to provide a second indication of a second temperature of the reference material. A processing device determines a concentration of the target gas based at least in part on a differential measurement between the first temperature and the second temperature.