Measurements of sulphur dioxide in rural air: data quality issues

Discrepancies between long-term average SO2 concentrations measured by UV-Fluorescence monitors in the AURN and DELTA denuders from AGA-Net are caused by inadequate performance of UV-F monitors at low concentrations. The hourly data are essential for measuring possible exceedances of limit values – for which the AURN was established – and there is no suggestion that they are no longer fit for that purpose. However, as operated at present they should not be used to provide data for assessing long-term average concentrations. The DELTA denuders in AGA-Net were specifically designed for that purpose, and provide the data needed to assess rural (and suburban) concentrations for model evaluation across the UK.