air quality assessment & management
Reference and User Manual
AirWare   On-line Reference Manual
  Release Level 7.0
  Revision Level beta
  Release Date 2015 03

VOC Speciation

Emissions of VOCs is usually from distributed, area sources rather than stacks, and due to evaporation rather than combustion processes as well as from biological processes.

Fugitive VOC emisisons originate from industrial and commercial areas and households (e.g., from chemical production processes, use of points and solvents), and the transportation (fuel) system.

Since the simulation models require more detailed emission data (in terms of chemical substances or "species") than are realistically measured, assumptions on the distribution of bulk data (VOC) are made referred to as speciation.

For the 3D dynamic photochemical model CAMx, AirWare uses the EPA speciation list ( ) to create CBIV lumped species from TOG (total organix gases) taken from:

The system does not differentiate by emission class. It assumes that the VOC values contained in the data base refer to non-methane organic compounds (the conversion factor for profile "0" is 1).

AirWare uses the default profile "0" for TOG .

The system also uses the default profile "0" for NOx conversion to NO and NO2:

Species NOx fraction
NO 0.90
NO2 0.10


Speciation profile "0"
Species description TOG fraction
ALD2Higher Aldehyde, based on Acetaldehyde 0.02
ETH Ethene 0.05
FORMFormaldehyde 0.02
OLE Olefin carbon bond C=C 0.05
PAR Paraffin carbon bond C-C 0.49
TOL Toluene and other monoalkyl aromatics 0.05
XYL Xylene and other polyalkyl aromatics 0.04
NR non reactives0.28

TOG (Total Organic Gases) is calculated from VOC:
TOG = factor*VOC (default: factor=1); values above one represent the Methane fraction.
The mass speciation factors for TOG are defined in the
default profile (#0) which can be overloaded by emission source class, type, and individual source. (Source:

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