Speciation is a model of E2Gov to process emissions data from Emissions for their use in the diffusion and transformation of pollutants models. This need is particularly relevant for the atmosphere even if similar requirements also exists in other environmental media such as water.

For a correct application of these models (eg CALGRID and CAMx), for the assessment of the chemistry of nitrogen oxides and ozone and evaluation of secondary particles, it is necessary to subdivide the emissions of nitrogen oxides, volatile organic compounds and suspended particles in the different chemical species.

This division is usually performed using speciation profiles; these profiles provide the share of each species or species class on total emissions.