The series of guidelines VDI 4280 describes the planning and evaluation of ambient air quality measurements and is an important element of quality assurance in monitoring and assessing air quality in the sector regulated by law (see acts, ordinances, administrative regulations in the Bibliography). The purpose of these guidelines is to ensure, in particular, the comparability of air quality characteristics from series of measured values of ambient air quality. However, this comparability of air quality characteristics is negatively affected by missing values in the series of measured values. Therefore, a method is described here that allows substitution of missing values in series of measured values of ambient air quality by using other series of measured values, for example those of adjacent measurement sites. The method for substituting missing values as described in the present guideline was validated in extensive investigations using real series of measured values. For this purpose, a programme was designed which is provided on a data carrier attached to this guideline. Annex A shows examples of substitutions of missing values that were carried out using this programme.