Spatial mapping of ozone and SO2 trends in Europe

This article investigates the spatial mapping of temporal trends in air quality for all of Europe. Such spatially distributed maps provide information for policy making and for understanding the spatial character of air quality trends. Previous trend studies have concentrated on individual, or groups of, monitoring sites looking at the trends of these. In this study use is made of statistical interpolation methods that combine observed and modelled data in an optimised way. Log-normal residual kriging with multiple linear regression is used to produce annual maps of air quality indicators for ozone (AOT40; Accumulated Dose of Ozone Over a Threshold of 40 ppb) and SO(2) (annual mean) for the period 1996-2005. Trends in these maps are then calculated and their significance and uncertainty are assessed. The methodology is effectively used for mapping SO(2) trends to a significant level in most of Europe. However, trends in AOT40 are less clearly defined since the uncertainty is generally of the same order as, or greater than, the calculated trends. A general north to south gradient in AOT40 trends can be seen, with downward trends in the UK and Scandinavia but upward trends in the Mediterranean region.