LAUSR

Abstract Aerosol problems in the ammonia-based wet flue gas desulfurization (ab-WFGD) system are of major concern in the field of atmospheric science. Previous studies stated that the heterogeneous reactions of SO 2 -H 2 O-NH 3 (the SO 2 reactions) are one of the major sources of the aerosol emission from ab-WFGD systems. In this paper, the aerosol formation from the SO 3 relating reactions (the SO 3 reactions) was investigated experimentally. The results were compared with those from the SO 2 reactions to distinguish the contributions they made to the aerosol emission. The influences of the corresponding parameters, such as the moisture content, the reaction temperature, and the NH 3 -to-SO 2 /SO 3 ratio (NH 3 /SO x ), on the aerosol formation were also explored. The results show that although the SO 3 concentration is lower than the SO 2 concentration, the aerosols formed by the SO 3 reactions are much more than those generated from the SO 2 reactions (numerical concentration). More than 90% of the aerosols are ultrafine particles. The aerosols formed from the SO 2 reactions are smaller than those from the SO 3 reactions. When the reaction temperatures increase above ~65 °C, the SO 2 reactions are hindered significantly while the SO 3 reactions are barely influenced. Higher moisture content can enhance the aerosol formation from the SO 2 reactions, but can hardly affect the SO 3 reactions. The increment of the NH 3 /SO x ratios boosts both the SO 2 reactions and the SO 3 reactions. When the NH 3 /SO 3 reached 2.0 and more, the aerosol formation from the SO 3 reactions stops increasing while the aerosol concentration in the SO 2 reactions keeps growing. Moreover, the parameter optimization methods were applied in a pilot-scale ab-WFGD system to evaluate the efficiency for aerosol emission control. The results show that decreasing the flue gas temperature before WFGD to around 80 °C can reduce the aerosol emission by ~20%. Adjusting the desulfurization solution pH to about 4.5 can decrease the aerosol emission by ~45% while keeping the desulfurization efficiency above 95%.