Normally the slow-response conventional gaseous-emission analysers based on non-dispersive infra-red measuring techniques are not widely used for measurement of transient engine-exhaust emissions, because the dynamics of these analysers distort emission signals during sampling processes. A phenomenological modelling approach is proposed which simulates the behaviour of gas transport through an emission analyser by a series of alternately arranged pipes and surge chambers, such that the distortion of the emission signal can be physically explained and modelled. The characterisation of an emission analyser by means of two physical models-viz diffusion and perfect gas-mixing models-is adopted as the basis for analysis, so that physical interpretation can be made to account for the resulting distortion and variation of measured emission signals. The actual emission signal before being distorted by the slow-response emission analyser can be reconstructed by solving these models numerically. A computer program has been developed which provides a continuous signal reconstruction from a series of distorted emission pulses measured during transient engine operation.