European scale application of atmospheric reactive nitrogen measurements in a low-cost approach to infer dry deposition fluxes.

A European scale network was established in 2006 as part of the NitroEurope Integrated Project to infer reactive nitrogen (Nr) dry deposition fluxes, based on low-cost sampling of gaseous and aerosol species and inferential modelling. The network provides monthly measurements of NH3, NH4+, HNO3 and NO3-, as well as SO2, SO42 , HCl, Cl- and base cations at 58 sites. Measurements are made with an established low-cost denuder methodology (DELTA) as a basis to: 1) examine temporal trends and spatial patterns across Europe, 2) improve and calibrate inferential modelling techniques to estimate exchange of Nr species, 3) provide best estimates of atmospheric dry N deposition, and 4) permit an analysis of net GHG exchange in relation to atmospheric and agricultural N inputs at the European scale. Responsibility for measurements is shared between seven European laboratories. An inter-comparison of the DELTA implementation by 6 laboratories at 4 test sites (Montelibretti, Italy; Braunschweig, Germany; Paterna, Spain and Auchencorth, UK) from July to October 2006 provided training for the laboratories and showed that good agreement was achieved in different climatic conditions (87% of laboratory site means within 20% of the inter-laboratory median). Results obtained from the first year of measurements show substantial spatial variability in atmospheric Nr concentrations, illustrating the major local (NH3)and regional (HNO3, NO3-, NH4+) differences in Nr concentrations. These results provide the basis to develop future estimates of site-based Nr dry deposition fluxes across Europe, and highlight the role of NH3, largely of agricultural origin, which was the largest single constituent and will dominate dry Nr fluxes at most sites