What are the different functions of activated carbon and HEPA in air purifier?

At present, the mainstream technology of air purifier on the market is the physical filtration technology based on activated carbon and HEPA.  So what are the roles of activated carbon and HEPA in air purifiers?  

Activated carbon is a kind of carbon material made of the appearance of black, internal pore structure developed, large specific surface area, strong adsorption capacity of a kind of microcrystalline carbon material, is a commonly used adsorbent, catalyst or catalyst carrier.  HEPA(High Efficiency Particulate Air Filter)  HEPA filters are 99.7% efficient for 0.1 and 0.3 microns. The characteristic of HEPA filters is that air can pass through, but fine particles cannot pass through.  It has a diameter of 0.3 micron (1/200 of the diameter of a hair) above the particle removal efficiency can reach 99.97% or more, is smoke, dust and bacteria and other pollutants the most effective filtration media.  

The HEPA filter layer in the air purifier is generally made into the shape of repeated folds.  This is because HEPA changes from a flat surface to a solid shape through repeated folding.  The larger the number of folds, the wider the width of folds, and the larger the actual expanded area, so as to effectively increase the contact area between HEPA filter element and polluted air, increase the ability of HEPA filter element to deal with polluted air, and extend the purification life of HEPA filter element.  The combination of activated carbon filter element and medical grade HEPA filter element in air purifier plays different roles in removing cigarette pollution.  

There are two main types of substances in cigarette smoke:  

1) Cigarette smoke particles (about 1 micron in diameter)  

2) Toxic and harmful gases including nicotine and carbon monoxide (the diameter of gas molecules is about 0.001 microns).  According to the filtration capacity of medical grade HEPA (which can filter air particles larger than 0.3 micron), cigarette smoke particles can be completely filtered by medical grade HEPA filter element.  But the medical-grade HEPA filter can not filter the toxic and harmful gases less than 0.3 micron in cigarettes, so it is necessary to purify the air with activated carbon for adsorption and removal.  Activated carbon can absorb all the toxic and harmful gases in cigarette pollution, including nicotine and carbon monoxide.  Therefore, activated carbon and medical-grade HEPA filters for air purification play a role in absorbing toxic and harmful gases and filtering pollution particles respectively in the process of removing cigarette pollution.  

Therefore, if an air purifier is only equipped with medical-grade HEPA filters or activated carbon filters, it can only filter the pollution particles of cigarette smoke or can only absorb the toxic and harmful gases from cigarette pollution.  Only air purifiers equipped with medical-grade HEPA and activated carbon filter elements can completely remove the pollution particles and toxic and harmful gases in cigarette smoke.