Spatial representativeness evaluation of air quality monitoring sites by point-centred variography

We propose a geostatistical technique based on point-centred semi-variograms that can be used to derive valuable information about the spatial representativeness of air quality monitoring sites. Whereas classical geostatistics describes the spatial correlation structure of a concentration field in terms of the variogram, point-centred variography is based on the average of squared concentration differences observed in pairs formed from a particular central point and the set of all other points in the domain. It thereby places a monitoring station in the context of the local or regional air quality pattern. We demonstrate how a mathematical inversion of the point-centred variogram can provide estimates of the extent of the representativeness area of a monitoring site. The application of this approach is tested on a set of modelling data from the city of Antwerp, which was used for the FAIRMODE/AQUILA intercomparison exercise of methods for the assessment of spatial representativeness.