Sensitivity of ammonia and particulate nitrate in Europe to dry deposition parameterization

Chemical transport models use different parameterizations for deposition processes. In the previous versions of the air quality model CAMx, the scaling parameter for surface resistance in dry deposition velocity calculations was set to zero for ammonia, leading to a fast deposition. In order to estimate ammonia removal rates more appropriately, in the new CAMx version 6.50, the scaling parameter was activated to include surface resistance in the deposition velocity calculations. The tests with the new parameterization in the United States showed that ammonia concentrations increased significantly leading to a better model performance. In this study, we simulated the European air quality in 2010 to investigate the effect of changing surface resistance parameter on the concentrations of ammonia, particulate nitrate, ammonium, sulfate and nitric acid. The results showed a significant increase in ammonia (30-60%) in central Europe, leading to a better model performance at most of the measurement sites. As a result of increased ammonia levels, nitric acid concentrations decreased by about 20-50% while nitrate and ammonium increased by 20 and 10%, respectively. The increase in sulphate was less than 10%.