I thought it would be an interesting project to build a detector that will measure and log the outdoor atmospheric CO2 levels. These (global average) levels are currently about 400ppm and these (global average) levels vary by a few ppm every year. Looking for a sensor though, I can't seem to find any that have an accuracy much better than ±30ppm. That is, unless I setup a spectrum absorption detector or something similar, but this might be a bit out of my price range, especially, since I was hoping to have a small circuit which I could run 24/7, constantly logging data, and running off a solar panel so I didn't have to do much to keep it running smoothly. Anyone know of a better solution? Perhaps an accurate sensor I missed? Or might the variation per measurement be enough that the ±30ppm would still give good average results? Thanks!