Abstract

Annual mean limits for NO2 concentrations have been set in the European Union, which will be most challenging to meet in large urban conurbations. In this paper, we discuss techniques that have been developed to predict current and future NO2 concentrations in London, utilising ambient data. Hourly average NOx (NO+NO2) and NO2 concentrations are used to calculate NOx frequency distributions. By defining relationships between the annual mean NOx and NO2 at different sites, it is possible to investigate different NOx reduction strategies. The application of the frequency distribution approach to monitoring sites in London shows that given the likely change in emissions by 2005, it is unlikely that much of central and inner London will meet the objective. The approaches used suggest that meeting the objective in central London will be the most challenging for policy makers requiring NOx concentrations as low as 30 ppb, compared with values closer to 36-40 ppb for outer London. Predictions for 2005 indicate that concentrations of NO2 up to 6 ppb in excess of the objective are likely in central London.