The display turns green when the CO2 concentration is 1,000 parts per million (ppm) or less, because the figure indicates the air indoors is being appropriately exchanged. When the meter was ...

This paper presents ground-breaking research on audience measurement across platforms, especially print, using the Arbitron Portable People Meter ™ (PPM) combined ...

Atmospheric concentrations of carbon dioxide have been steadily rising, from approximately 315 ppm (parts per million ... Atmospheric CO2 records from sites in the SIO air sampling network.