Here is some new data from a gas sensor. This is a module with a CCS-811 sensor (provides an estimate of total volatile organic compounds [VOC]). These modules cost about $10 on eBay. I had two of these running for four weeks in my office on separate data loggers. Both sensors recorded similar variation in total VOC (Figure 1). This suggests that whatever is being measured is being measured somewhat consistently.
Figure 1. Four weeks of data from two CCS-811 VOC sensors in my office. The two sensors were a few inches apart. Each dot is the mean of 60 sensor measurements taken once per second and saved once per minute.
Both of the data loggers also recorded data from a Plantower PMS7003 particulate matter sensor (similar to the sensor in a PurpleAir sensor). Having results from these two sensors together helps immensely when interpreting the results of either. Although I recorded what was happening everyday in the room where the sensors were, it was not always obvious what the sensors were responding to. Lots of activities in the room produced particulates and gases including soldering, 3D printing, room heater with a fan, and human body stuff. Some of these activities produced only particulates, some only gas, and some both (Figure 2).
Figure 2. Four weeks of data from a CCS-811 VOC sensor and a Plantower PMS7003 particulate sensor. The two sensors were two inches apart. Each dot is the mean of 60 sensor measurements taken once per second and saved once per minute.
If I really wanted to have the best chance of interpreting what type of air pollution was being recorded, I would also add a temperature and humidity sensor. I would also keep a detailed log of what was happening near the sensors.
Ooh interesting. Yeah could imagine interesting things related to, say, cleaning products, gas stoves, even paints or dry but treated surfaces... plywood, carpets, all possibly producing VOCs. I guess this calls for some kind of complex but repeatable dance routine to sequence a bunch of interactions with these materials.