This citizen science project aims to provide as high a quality data-set as is possible given the limitations inherent in the equipment and calibration methods (see ‘About’ for more details). The accuracy of the data will not match that provided by more sophisticated equipment, but should provide a good indication of the prevailing carbon dioxide concentrations at each site. Note that local sources and sinks can influence the measurements, although every effort has been taken to place sensors so as to minimise such influences. The data is intended for educational purposes primarily, and should not be used to inform decisions without additional verification.