Emissions of combustion processes can be classified in two
groups: input specific (input dependent) and process specific (process dependent) emissions (Riber et al., 2008). Some emissions belong to both categories, e.g. NOx: fuel–NOx (originating from the
oxidation of fuel-bound nitrogen) is input specific, whereas thermal NO
x (originating from the oxidation of nitrogen in the air) is
process specific (Hill and Smoot, 2000; Glarborg et al., 2003). Emissions related to the formation of by-products (and by extension
waste) and to the production of consumed reagents can be classified as input or process specific emissions depending on the
respective by-product or reagent. For instance, NH3 consumption
related to fuel–NO
x is input specific, whereas CaO consumption
(removal of acid gaseous pollutants) is process specific.