EMEP Intensive Measurement Periods 2008/09 at Råö. Paper presented at the 10th TFMM meeting in Paris, 15-17 June 2009

IVL has participated in the intensive measurement periods 2008/2009 within EMEP by performing denuder measurements of NH3/NH4+ and HNO3/NO3- on a 24 h basis. Measurements were performed at Råö on the Swedish west-coast. In earlier investigations the denuder for HNO3/NO3- was coated with carbonate in order to also obtain the SO2 concentration. A small positive interference in the HNO3 determination from other oxidized nitrogen compounds can then occur. To avoid that interference the denuder was coated with chloride instead of carbonate. The EMEP station Råö is performing filter pack sampling since 1986. Since the filter pack results are reported as gas and particle phases separately, the results from the denuder measurements were compared to the filter pack results. The total (gas + particle) concentrations agreed very well between the two sampling techniques. However, the filter pack overestimated the ammonia concentration and underestimated the particulate ammonium concentration. The filter pack was surprisingly good at separating gaseous nitric acid from particulate nitrate.