Analysis of information sources in references of the Wikipedia article "Cement kiln" in English language version.
The IPCC recommends using clinker data, rather than cement data, to estimate CO2 emissions because CO2 is emitted during clinker production and not during cement production. The Tier 1 method uses the IPCC default value for the fraction of lime in clinker, which is 64.6 percent. This results in an emission factor of 0.507 tons of CO2/ton of clinker