activity data

the amount of fuels or materials consumed or produced by a process relevant for the calculation-based methodology, expressed in terajoules, mass in tonnes or, for gases, volume in normal cubic metres, as appropriate

Activity data is the measured quantity of a fuel or material actually consumed or produced by a source stream — expressed in tonnes, terajoules or normal cubic metres, depending on the input. It's combined with calculation factors like emission factor and calorific value to work out an installation's direct emissions, and has to be documented in the site's monitoring plan alongside every source stream it relates to.