GSS tests LED-based CO2 sensor in cars
At CO2 levels of 1000 ppm and above people can become drowsy and lethargic. Carbon dioxide sensor specialists Gas Sensing Solutions (GSS) wondered whether the sleepiness we feel on long car journeys could be due to this build-up of CO2 gas.
"This follows on from our trip to Asia where we used our CO2 datalogger to measure CO2 gas levels on planes, trains and taxis. We were surprised that levels were the worst in taxis - peaking at an astonishing 10000 ppm on one journey - so we decided to check the levels on our own road trip in the UK," explained David Moodie, technical manager at GSS.
It used a battery-powered datalogger based on its low power proprietary LED-based CozIR-A sensors. Before the datalogger took to the road, it was first used to test CO2 levels in a stationary car. This would show the impact on CO2 levels with a group of four people in a confined space. The engine was switched off and the windows kept closed to avoid any flow of fresh air inside the vehicle. The datalogger showed that when the passengers got inside the car, the CO2 level was 1000 ppm. It then rocketed to almost 4000 ppm in just 15 minutes.
Next came the road trip. The first car journey involved two people travelling to the supermarket. The CO2 from their exhaled breath increased the concentration of CO2 in the car cabin to around 1400 ppm. It only took about forty-five minutes to reach this level. The datalogger was then left in the car overnight with the windows closed. (The graph shows just how long it takes for the CO2 to disperse from a closed car, taking until around 9am the next day to drop down to nearer ambient levels of CO2.)
The second car journey recorded four people travelling non-stop from Wales to Scotland. With four people, the level of CO2 shot up even faster, reaching 2000 ppm in about twenty minutes. This is the level where CO2 symptoms can start to cause loss of concentration, headaches and sleepiness for example. Fortunately, they opened the windows to bring in fresh air from outside, which reduced the CO2 to more acceptable, ambient levels within an hour.
"Our real-world datalogger measurements show how CO2 levels can rapidly build up in an enclosed space with several occupants - and in a relatively short space of time too. The results on both journeys exceeded The World Health Organisation* guideline that CO2 levels should be below 1000 ppm," said Moodie
"This ability to be battery powered for long periods has opened up a whole new range of design possibilities for CO2 monitors. Now it's possible to have handheld breath monitors with high speed sensing for people with respiratory conditions, portable leak detection instruments, handheld MAP analysers, and wireless air quality monitors for IoT applications. These are just a few examples of what is achievable, the possibilities really are endless."
Most CO2 sensors work by measuring how much light is absorbed by CO2 molecules in the 4.2 to 4.4 microns range as it passes through the sample gas, which is called Non-Dispersive Infra Red (NDIR) absorption. The amount of absorption indicates how much CO2 is present. GSS developed proprietary LEDs that are specifically tuned to emit at these wavelengths. The LEDs use very little power and turn on almost instantly, enabling sensor readings to be made in a few seconds. As a result, GSS has pioneered the development of CO2 sensors that can be powered by batteries for long periods of up to ten years.
