Modelling the deposition of atmospheric oxidised nitrogen and sulphur to the United Kingdom using a multi-layer long-range transport model

Deposition of sulphur and oxidised nitrogen have been estimated for the United Kingdom (UK) for 1996 using an atmospheric transport model (FRAME, Fine Resolution Atmospheric Multi-pollutant Exchange). Firstly, the modelled deposition is compared with measurement based estimates of NEGTAP (National Expert Group on Transboundary Air Pollution). Secondly, the modelled wet deposition and surface air concentrations are compared with measurements from the UK's monitoring networks using linear regression. FRAME gives 65 and 102 ktonnes(kt) for oxidised nitrogen dry and wet UK deposition, respectively, compared with the NEGTAP estimation of 87 and 91 kt . The modelled contributions of sulphur dry and wet deposition are 138 and 200 kt , respectively, compared with the NEGTAP estimation of 125 and 171 kt . FRAME is found to perform well for nitrogen dioxide concentrations and nitrate wet deposition, but the concentration and subsequent dry deposition of nitric acid is underestimated. Deposition of sulphur and sulphur dioxide surface concentrations are coherent with the NEGTAP estimation but they are slightly overestimated by FRAME. The paper also emphasises the uncertainties associated with the model when used to assess the effects of abatement policies.