Sensitivity analysis of an ammonium salt formation model applied to pollutant removal in marine diesel exhaust gases

Abstract

Elevated exposure to airborne pollutants such as NOx and SOx is known to be damaging to human health. A current approach to deal with such harmful gases is to trap them in ammonium salt particles. The present study presents the sensitivity analysis of the aerosol model for ammonium salt particle formation from NOx and SOx for low-temperature gas cleaning applications developed by Olenius et al. (2021). Starting from the acid gases derived from NOx and SOx (i.e. HNO3 and H2SO4), the model simulates the particle growth phenomena as the acids react with ammonia (NH3). This work presents, for the first time, a global sensitivity analysis of the aerosol model uncertainty. The first- and total-order effects of five different input variables on model outputs such as particle size distribution, pollutant removal effectiveness, ammonia slip, and total run time are reported. Furthermore, the range of input parameters for which the model is tested is made to emulate the conditions experienced by two-stroke marine diesel engine ships. Sources of uncertainty are reviewed in detail to provide a complete view of the knowledge gaps in the particle conversion process. For the conditions studied, we report that variations in particle sizes are influenced by HNO3, H2SO4 and temperature. Similarly, the degree of ammonia slip was observed to be driven by temperature and the ammonia ratio. Additionally, the removal efficiency of HNO3 was reported to be very high (above 99%) for the vast majority of conditions tested, and was not significantly influenced by the concentration of H2SO4. Finally, the model run time variability was observed to depend mainly on variations in temperature, relative humidity and the ammonia ratio.