being largely human-made and relatively recently created, pm (particulate matter) and voc’s (volatile organic compounds), and perhaps rarer (but potent) pollutants like ozone, carbon monoxide, and radon, are important to monitor for health. note that co2, while fashionable to be concerned about these days, is not a significant health concern (life evolved in relatively significant concentrations of co2) beyond suffocations at extremely high concentrations.