Ionic Air Filters
Also called air ionizers, ionic air filters rely on voltage to charge air molecules. Typically, they produce negatively charged ions, also called anions, which then attract particles in the air, in much the same way as static electricity. As the particles make contact with the anions, they are deionized and removed from the air stream. Ionic air filters are commonly used in commercial air filtration.
HEPA Air Filters
HEPA (high efficiency particulate absorbing) filters are stronger and more effective than ionic air filters, and are therefore preferred by sensitive applications—HEPA filters can remove up to 99.97 percent of airborne particles, making them extremely effective air sanitizers. The filters are primarily comprised of fiberglass fiber mats, which trap particles as an air stream flows through. How effective a HEPA filter is largely depends on the diameter of the fiber and the filter’s thickness.
HEPA filters trap particles using several different approaches. First, they intercept particles as the air flows through the filter, and particles within close proximity to a fiber are caught and trapped. In addition to interception, increasing air-flow and curving the air stream can instigate impaction, as the particles directly collide with the fibers and are caught. Diffusion is a process that uses gas collision to separate the smallest particles, slowing them down as they pass through the filter and increasing their chances of getting caught by a fiber. Because of HEPA filters’ high level of efficiency, they are commonly used in the medical sector to remove bacteria and prevent contamination, and are often used in clean rooms and highly sanitized hospital wards.
Carbon Air Filters
Carbon can be treated with oxygen, which opens the carbon’s pores making it highly absorbent. After this treatment, carbon is said be activated because it can readily be used to absorb particles and trap odors. Carbon air filters use activated carbon to trap chemicals and gases, and can also filter cigarette smoke. As the air passes through the filter, the activated carbon absorbs the odors and gasses and neutralizes them. For seriously odiferous fumes, activated carbon can be impregnated or enhanced so as to absorb the given gas. Activated carbon filters are well-suited to environments where chemicals must be removed from the air.
UV Light Air Filters
Ultraviolet light air filters use a reaction that occurs when titanium dioxide is exposed to UV light. As the air stream encounters the photochemical process, harmful particles, such as mold and bacteria, are neutralized. High intensity UV (240-280 nm) is strong enough to break down most carbon based organic compounds, making UV light air filters a good companion to HEP filters in medical applications. How effective UV light filters are is contingent upon the length of exposure (how long the air stream is subjected to the light) and the intensity of the light itself.