Filtration and air purifiers

HEPA filter or High efficiency particulate arrest , are seen in many products these days inclusive of vacuum cleaners. They have a filtration capacity of 99.97&% particles of size in 0.3 micrometres

This is based on a nominal statical resistance to airflow of 300 pascals. (not bad).

These are nothing new and have been around since the 1940's as a way of trapping radioactive contaminants. They were key in the prevention of spread of bacterial and viral agents. 

When coupled with a high intensity ultra-violet light could kill of the live bacteria trapped inside the filter media

Negative ion generators are an electrical device that uses high voltage to ionize air molecules with extra electrons to make them negatively charged. Most airborne dust contaminants have a positive charge which then become attracted to the negative ion's
This increased their molecular weight and they become heavy falling lower where they are less likely to be inhaled. They are also likely to become trapped in filters as their molecular density has increased. Negative ions are produced in nature by waterfalls etc , which is why we feel so much better when we are near them.

This is why we feel better in a negative ion environment rather than a positive ion atmosphere. It is said as they remove the contaminants , they have a rejuvenating effect on the bodies respiratory system.

Now if you have not been paying attention , there are air purifiers in the market. They consist of a pre filter, anti bacterial filter , ionizing grid, UV lights and negative ion generator.

They work, I have one , but one caution!

They do not filter noxious gases like carbon monoxide. 
They will clean up a stale , smokey , room

Brilliant technology. Cheap, cheap cheap to run