Some Organic Indoor Pollutant Classifications by WHO

Appendix 2.A.1 Some Organic Indoor Pollutant Classifications by WHO 

The World Health Organisation (WHO) classifies organic indoor pollutants according to their boiling points (bp), as follows  

The VVOC and VOC are mostly due to non-bound, rather low molecular-weight organic molecules (also called as free or primary emissions) that exist in the system. 

However, there are cases where bound organic molecules, or some parts of the system itself, can also contribute to VOC and VVOC emissions, if there is any special effect that can break them down from the system (e.g., thermal, chemical or mechanical degradation), and these are termed secondary emissions. 

VOCs are mainly hydrocarbons (2.73 Mt in 1997 in the UK) and the most abundant is methane (50% from landfills, 30% from animals, and rest from gas extraction, biomass burning) while non-methane VOC in 1997 in the UK (2.13 Mt in the UK) are mainly emitted from vehicles (40%), from solvents in paints (30%), etc., which is composed of some 200 different hydrocarbons such as benzene and toluene [34], 

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