35 ILCS 110/2a
"Pollution control facilities" means any system, method, construction, device or appliance appurtenant thereto used in this State acquired as an incident to the purchase of a service from a serviceman for the primary purpose of eliminating, preventing, or reducing air and water pollution as the term "air pollution" or "water pollution" is defined in the "Environmental Protection Act", enacted by the 76th General Assembly, or for the primary purpose of treating, pretreating, modifying or disposing of any potential solid, liquid or gaseous pollutant which if released without such treatment, pretreatment, modification or disposal might be harmful, detrimental or offensive to human, plant or animal life, or to property.
Until July 1, 2003, the purchase, employment or transfer of such tangible personal property as pollution control facilities is not a purchase, use or sale of service or of tangible personal property within the meaning of this Act.
35 ILCS 110/2a