Surprised by how high levels were on some occasions, GSS will be doing further investigations in other locations to see how CO2 levels vary in the real world.
The datalogger used measures CO2 concentration, air pressure and temperature along with relative humidity every few minutes. It is a custom solution designed and built by GSS and uses one of its low power, ambient air, CozIR-A 5000 sensors. This low power consumption enabled the datalogger to record over a 2-week period without needing a change of battery. The other sensors integrated in the module are an NXP MPL3115A2 pressure sensor and a Sensirion SHT21 temperature and humidity sensor.
The recorded data shows how the CO2 level in blue and the air pressure level in green fluctuated throughout the journey. It clearly shows increased levels of CO2 when there are a number of people in a confined space with limited ventilation to remove CO2 build up. The World Health Organisation guideline is that CO2 levels should be below 1000 ppm, and ASHRAE (the American Society of Heating, Refrigeration and Air Conditioning Engineers) says that CO2 at high concentrations of 5000 ppm can pose a health risk.
The drop in air pressure on the graph shows the part of the journey that was in a plane. The train journeys show particularly high levels of CO2, where CO2 levels built up to over 2000 ppm. Similar results are shown from the meeting room. However, perhaps surprisingly the highest CO2 peaks were during the taxi journeys with two passengers and a driver. This consistently produced levels in excess of the 5000 ppm health risk indicator mark and, at one point of the journey, even peaked at 10,000 ppm. This really shows the high levels of CO2 that people can be exposed to while driving through a busy city.