The class was divided into several groups each with a beaker of boiling water and a temperature sensor. Packets of salt, in various amounts, were distributed to each group. Each groups' water temperature was displayed on the computer screen. Based on the variation in boiling temperatures, the students had to decide which groups had same amount, which had more, and which had less salt. Indoor air quality is a very difficult and costly parameter to measure.
Carbon dioxide is the least expensive gas to measure and serves as a good measure of ventilation.
Normally present in outdoor air at a concentration of 380 ppm, CO2 is exhaled by humans. By monitoring CO2, students can obtain an excellent indication of indoor air quality. One school measured concentrations in excess of 1500 ppm in classrooms. Some states consider concentrations above 1000 ppm unhealthy and indicate that more ventilation is needed. One professor took the sensor home and measured concentrations over 2000 ppm.