Parallels can also be drawn between volcanic plumes and a similarly extreme environment: industrial flue gas. GEM is commonly removed from flue gas by injection of fly ash or activated carbon, which leads to efficient GEM scavenging within minutes. The underlying process appears to be mainly chemisorption , i.e. irreversible reactive Hg uptake involving a chemical reaction between Hg and active sites (adsorption sites) on the particle surface. Indeed, GEM removal is enhanced if the aerosol was impregnated (i.e. pre-treated) with halogens , or sulfur . Sulfur impregnation greatly increases the abundancy of sulfite and sulfates (especially sulfuric acid) on particle surfaces and within pores, compounds that likely act as Hg adsorption sites to generate HgSO4 90,92,98-101 , which is very stable at ambient temperatures 93 .