Described is a selective catalytic reduction catalyst comprising an 8-ring small pore molecular sieve promoted with copper and an alkaline earth component. The voltage regulating circuit includes a voltage regulator, a converting circuit, a capacitive device, a first current mirror module, and a second current mirror module. A liquid storage container is located in the housing and has means for dispersing liquid in the container into the stream of air adding a liquid mixture containing nitrogen, free citrus extract and colloidal silver into the liquid storage container and vaporizing the liquid mixture in the air stream for dispersing the liquid mixture into the surrounding air along with positive and negative ions.