A small air purifier helps to eliminate bacteria and other contaminants either by electrostatic attracting particles or else by killing bacteria using ultraviolet lights. This system is more affordable than ultra-fine filters that require powerful pumps in order to force air through. A commercial air purifier might use the same techniques but at a much larger scale. Killing unwanted bacteria or else removing them for a large building is quite a trick, but worth it if the residents need it.
A commercial unit might use fine filters but will likely use other means to purify the air include electrostatic cling or ultraviolet light. Regular sunlight is known to kill bacteria outdoors, and the same process can be fabricated indoors using intense UV light and cycling indoor air through it. Using a combination of methods helps to achieve greater energy efficiency over a hospital grade filter which requires a very powerful air pump.
