This part of the European Standard describes the grid method for the determination of the level of exposure to odour in ambient air. It provides a set of instructions for measurement of ambient odour exposure within a defined assessment area, using qualified human panel members, over a sufficiently long period of time to be representative for the meteorological conditions of that location, and hence determine the distribution of the frequency of exposure to odours within the assessment area. The sources of the odour under study may be located within or outside the assessment area. The primary application of this European Standard is to provide a common basis for evaluation of exposure to ambient odours in the member states of the European Union. The field of application of this type of measurement is to characterize the level of odour exposure within the study area, in order to assess whether the impact of that exposure on resident population could be a justified cause for annoyance, using exposure criteria. The unit of measurement of the method is the frequency of odour hours for an assessment square, defined by four measurement points as a representative value for odour exposure for local conditions, e.g. local odour sources and the meteorology of that location. This European Standard does not include: the measurement of intensity of ambient odours, the measurement of hedonic tone of ambient odours, the calculation of odour exposure in specific weather conditions in order to determine the frequency distribution of recognizable odour in an odour plume, the calculation of estimated source emission rate from plume assessment using reverse dispersion modelling. An overview of the interaction between existing odour exposure assessment methods is given in Annex A including grid method (Part 1), plume method (Part 2) and olfactometry according EN 13725.