Similar to steam modification, gas purging modification alsoinvolves two process. The first is the pyrolysis of feedstock. Thesecond is to modify the biochar by purging carbon dioxide orammonia gas. Gas purging modification can increase the surfacearea of biochar and improve the structure of biochar, which furtherenhances the adsorption capacity to gas. Carbon dioxide modifi-cation can promote the formation of pore and improve the structure of micro-porous