just a side note - while specific industrial testers may be overkill, the combined CO2/particulate/VOC/formaldehyde gadgets are $100 ballpark, and given the new construction on sites where Intel/HP dumped the etching fluids or whatever, buildings energy saving certifications (read low ventilation/AC), etc. i find it is very useful to have on desktop in the office (watching formaldehyde (or may be VOC - forgot after 2 years WFH) rising on a hot day on new furniture, though still under official safety limits. The CO2 was almost always under 600 - not bad :)