Uncertainties in the compilation of spatially resolved emission inventories — evidence from a comparative study

This paper examines the nature and extent of uncertainties associated with spatially resolved emission estimates with particular reference to an examination of alternative emissions data. Evidence is taken from recent research into the development of generic methodologies for the estimation of emissions of key urban pollutants from anthropogenic sources in the North West region of England. The inventory results, which are available in terms of a regional 5×5 km grid, a sub-regional 1×1 km grid and at the scale of the original activity data, are useful for a number of air quality management tasks. However, the requirements of producing a generic methodology which uses readily available data sources has been found to limit the degree of detail with which it is possible to develop estimation procedures and this has implications for the level of confidence associated with the results and their further application. One of the principal limitations is the availability of equivalent activity data for a number of administrative units. A further assessment of the results of the North West inventory has been made through a comparative study of the inventory data with other emissions data covering a sub-set of the study area. These investigations indicate that there are a number of variations between inventory results in terms of overall emission magnitudes and their spatial distribution. Observed differences between the estimates are attributable to different sources of activity data and emission factors and also as a result of the geographical data used to represent sources.