Using wind-direction-dependent differences between model calculations and field measurements as indicator for the inaccuracy of emission inventories

In forward air quality modelling, an emission inventory is used as input into an atmospheric dispersion model to calculate atmospheric concentrations of the pollutant. Differences between calculated concentrations and concentrations found by atmospheric measurements can be used as an indicator for the inaccuracy of the emission inventory used in the calculations. The problem with comparing calculated and observed concentrations is that it is not easy to pinpoint the emission inventory as a single cause for the differences. One of the reasons for this is that inaccuracies exist in the model, both in measurements and in the inventory. In this paper. we argue that when wind-direction-dependent differences at several measurement stations in different countries point towards a specific region, the emission estimate for that specific region is the likely cause for the differences between modelled and observed concentrations. We have applied this methodology to study the inaccuracies of a European SO2 emissions inventory for 1994, by plotting the calculated SO2 concentrations from a long term ozone simulation model with SO2 concentrations measured in the EMEP network. The results show that we were able to identify inaccuracies in the emission inventory for several areas within Europe. These areas include Sachsen/Brandenburg (Germany), Central England and the Western part of the Russian Federation. Although this type of analysis is accompanied with several limitations, it could provide the emission inventory community with a relatively simple technique to identify inaccuracies in the emission inventory. (C) 2002 Elsevier Science Ltd. All rights reserved.