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    You didn’t mention it in your post, but in general CO2 sensors should be calibrated or you will be getting reading that are off. https://www.yoctopuce.com/EN/article/how-to-calibrate-a-co2-sensor

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      yoctopuce seems to have some fine products, but holy hell are they pricey - and the calibration kits (coming from senseair) aren’t even available without contacting sales, so I guess as a private person you won’t normally get them

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        It looks like you have 2 options for calibration. You can either move the sensor outside and run the calibration procedure. That assumes that the outside air CO2 concentration is 400 ppm and resets the sensor accordingly. Or, you can buy one fo thoe calibration kits . The kits usually involve using nitrogen gas to eliminate all CO2 from the sensor, leading to it calibrating to a “true zero” value instead of a 400 ppm value.

        The outside method works most of the case but it might be a little bit off in case the CO2 ppm concentration is higher in your area for whatever reason.

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      Also checkout sensor.community which a community project to collect air quality all over the world and make the data visible for everyone worldwide.

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        “So far, the data is (thankfully) pretty “boring”. The PM2.5 near my home is close to zero at baseline, and doesn’t change meaningfully in normal conditions.”

        Have you considered keeping it around in your kitchen? I’ve found an air quality monitor (looking at voc/pm2.5 in particular, such as the wynd) to be really helpful in reminding oneself around better ventilation when cooking.

        see https://www.newyorker.com/magazine/2019/04/08/the-hidden-air-pollution-in-our-homes

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          Great writeup on a cool project.

          See also https://www.purpleair.com/map?opt=1/mAQI/a10/cC0#14.82/47.67542/-122.31702 I have no affiliation, just learned about it a couple days ago. They use the same PSM5003 laser scintillator module for counting particulates. The board you linked to is much more featureful.

          It looks like you a little close to I-5, it would be neat to have a sensor right next to the highway and measure the fall of in particulates wrt your location. LoRA and solar would be a great extension to this project, allowing for more sensors in more places.

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            these are all low-end consumer-grade sensors

            SenseAir S8 CO2 Sensor ($29.12)

            Well, that looks significantly less low-end than the MQ family sensors!

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              If you’re ok with fewer / less precise measurements, you can also slap some cheap sensors onto the i2c pins on a raspberry pi. CCS811 does eCO2 and VOC and has cheap breakout boards for example. It’s fun if you’re up for just a little bit of soldering.

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                CCS811 does eCO2 and VOC and has cheap breakout boards for example

                Neat! I hadn’t heard of that sensor before

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                  Just be patient with the setup. The initialisation is really temperamental and there are two “status” commands with similar output - you’d think both work in all modes, but no…