Ratification is a process whereby the "raw" data that is collected from an analyser is checked to ensure its validity. This entails examination of the data to verify that concentrations are not too high or too low, checking of "drift", where an analysers performance can change over time and calibration of the data against traceable standard gases.
Because the ratification is done a month at a time, the most recent data appearing on http://www.bristol.airqualitydata.com are not ratified. The data before the beginning of the current month are ratified. Meteorological data are not subject to the ratification process.