What can a good filter/purifier NOT do?

There are certain controversies that arise when it comes to a good filter/purifier. For instance, an air purifier exerts an anti-ozone gas. This anti-ozone gas secretes substances that affect the nature's condition and can destroy the ozone layer.

Another thing, there are some filters/purifiers that can only sort out microbes but it cannot eradicate it completely, so as an effect of this those microbes continue to grow inside the filters/purifier.

--- permission must be obtained from author Edward Parry to re-publish ---