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The volatile contaminants

 

Two families of volatile contaminants have to be abated:

  • the odorous molecules

  • the toxic molecules, that are often odourless
1. the odorous molecules

 

The disturbing odours are often produced by highly volatile molecules with very low odour threshold, like ammoniac (NH3), hydrogen sulphur (H2S) and mercaptans (CxHy-SH), which means that they can release odours at very low concentration.

 

Most of them are non toxic as long as their concentration is low. Thanks to their small structure, they can be easily oxidized by soft oxidation processes, like a high concentration of air ions with a micro-concentration ozone.

 

2. the toxic molecules

 

Toxic molecules, that can be found in our indoor environment, are either produced outdoor or indoor. Some of them have been classified in the European Norm 67/548/EEC, recommending maximal admissible concentrations:

 
  • Outdoor sources:

Houses nearby specific locations can accumulate specific toxic organic molecules in their indoor:

 

Neighbourhood

 

Emission

 

Toxic molecules

 

Field

 

 

Pesticide emissions

 

various toxic molecules; among them the POP (Persistent Organic Pollutants)

 

Road

 

Car emissions

 

benzene (used instead of lead !)

Industry

 

Process emissions,
Combustion process at high T

various solvents

dioxine

 
  • Indoor sources:

 

Materials

Toxic molecules

 

Painting & diluents

xylene, toluene, MIBK

 

Glue & resin

formaldehyde, phenol, styrene

 

Tobacco

benzene and benzene derivates

 

Polystyrene

styrene

 

Petrol

benzene

 

Wood based panels

formaldehyde, PCB, PCP

 

Textile

formaldehyde

 

Insulation foam & synthetic carpets

Formaldehyde, styrene

 

Dry cleaned clothes

 

tetrachloroethylene

Flame retardant for plastics,
textiles and synthetic rubber

 

PBDE

 

Plasticizer in PVC products (roof, floor and wall coverings

 

DEHP

 

 
Most of these molecules are carcinogenic but can be easily adsorbed on activated carbon, except Formaldehyde and PCB are too volatile and need oxidation or chemical adsorption technologies.

 

Impact on human health:

 

The symptoms due to solvent poisoning are: narcotic effect, skin allergy, eyes and mucus irritation, dizziness, nausea, headache, fatigue. Certain persons can develop problems of hypersensibility. Continuous exposition to some carcinogenic molecules like benzene (cigarette, petrol station) or formaldehyde can lead to cancer (see next table).

 

Impact on the Air Purification or Conditioning Concept

 

It is the chemical structure and the toxicity of the molecule that determine the choice of the abatement technology:

 

Volatile compound

 

Technology

 

Very low concentration - non toxic and/or very volatile (NH3, H2S,...)

air ions &
micro-concentration ozone
 
 
Very low concentration - toxic and/or heavy molecules (aromatics,...)
 
activated carbon
Formaldehyde
 
iono-catalysis
Higher concentrations - any kind of molecules

 

photo-catalysis

 

 

© 2008 Air Quality Concept