Updating CBED modelling data on the Air Pollution Information System

The acid and nutrient nitrogen deposition data sets used in APIS are based on CBED model.  Recently, CBED model results from 2004 to 2013 have been updated following a quality control study by NERC CEH and Defra (report under review).  The CBED model uses chemical concentration data measured on monthly or fortnightly periods at UKEAP sites across the UK.  The study assessed the DELTA sampler configuration’s specificity for HNO3 measurement and showed additional sampling of other atmospheric oxidised nitrogen species (HONO, N2O5, ClNO2) i.e. the tests highlighted a systematic overestimation in HNO3 concentrations by the original UKEAP measurements.  As a result the method is being changed.  For data using the original method, a correction factor has been calculated and applied to revise previous HNO3 concentrations used in the CBED mapping and therefore in the APIS data.  This correction factor was considered and approved during a meeting of end users (modellers) and the research team. It is noted that the deposition of other atmospheric oxidised nitrogen species (e.g. HONO, N2O5, ClNO2) are not assessed in UKEAP or CBED.