Modelling of sea salt concentrations over Europe: Key uncertainties and comparison with observations
Sea salt aerosol can significantly affect the air quality. Sea salt can cause enhanced concentrations of par- ticulate matter and change particle chemical composition, in particular in coastal areas, and therefore should be ac- counted for in air quality modelling. We have used an EMEP Unified model to calculate sea salt concentrations and de- positions over Europe, focusing on studying the effects of uncertainties in sea salt production and lifetime on calcula- tion results. Model calculations of sea salt have been com- pared with EMEP observations of sodium concentrations in air and precipitation for a four year period, from 2004 to 2007, including size (fine/coarse) resolved EMEP intensive measurements in 2006 and 2007. In the presented calcula- tions, sodium air concentrations are between 8 % and 46 % overestimated, whereas concentrations in precipitation are systematically underestimated by 65–70 % for years 2004– 2007. A series of model tests have been performed to inves- tigate the reasons for this underestimation, but further studies are needed. The model is found to reproduce the spatial dis- tribution of Na+ in air and precipitation over Europe fairly well, and to capture most of sea salt episodes. The paper presents the main findings from a series of tests in which we compare several different sea spray source functions and also look at the effects of meteorological input and the efficiency of removal processes on calculated sea salt concentrations. Finally, sea salt calculations with the EMEP model have been compared with results from the SILAM model and observa- tions for 2007. While the models produce quite close results for Na+ at the majority of 26 measurement sites, discrepan- cies in terms of bias and temporal correlation are also found. Correspondence to: S. Tsyro (email@example.com ) Those differences are believed to occur due to differences in the representation of source function and size distribution of sea salt aerosol, different meteorology used for model runs and the different models’ resolution. This study contributes to getting a better insight on uncertainties associated with sea salt calculations and thus facilitates further improvement of aerosol modelling on both regional and global scales.