The determination of odour in ambient air by field inspections using the grid method is a method that has been used in Germany for decades to determine the frequency of exposure to odours in an impact area. The method which is currently described in EN 16841-1:2016 is a statistical survey which is applied over a sufficiently long period of time. It delivers a representative map of the exposure to recognizable odour(s) with its distribution over the assessed area. Within this paper the principle of measurement will be briefly described, as well as the challenges that might occur during a project and the possibilities that arise from the detailed measurement of odour frequencies in the impact area. Often the question arises whether the sample of 104 single measurements per assessment square and year is sufficient. Olfasense GmbH has been carrying out yearly field surveys in the vicinity of an industrial plant since 2009. In contrast to the procedure described in EN 16841-1:2016-11, the field surveys take place on a daily basis in this project. This results in 365 single measurements per assessment square and year. The time of day is varied according to the standard.
This extensive data set including 365 single measurements is used as reference survey. Subsequently, the same data was randomly divided into 3 individual data sets (sample surveys 1 to 3), each including 104 single measurements. For each data set the results including the measurement uncertainty according to EN 16841-1:2016 are evaluated for the single assessment squares. With a comparison of the reference survey (365 measurements/year) with each of the sample surveys (104 measurements/year) the reliability of each sample survey can be determined. As the sample surveys represent the required scope of measurement according to the European Standard EN 16841-1:2016 a validation of the usual extent could be performed. The results of this evaluation show that 104 single measurements per assessment square within one year, as reflected in the sample surveys, are sufficient to make a statement on the compliance with the permissible odour exposure in the impact area, taking into account the measurement uncertainty contributions.