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Fluid catalytic cracking (FCC) unit emits a large amount of flue gas, which is a major concern of environmental protection supervision. Wet flue gas desulfurization (WFGD) technologies have been widely used to control the emissions of SO 2 in refineries. In this study, stack tests for pollutants emission of a typical FCC unit were conducted. The emission characteristics of the FCC unit indicated that WFGD would cause a large amount of water vapor in the flue gas, which indirectly leads to large quantities of salt pollutants entrained in the flue gas including ammonium sulfite ((NH 4 ) 2 SO 3 ) and ammonium sulfate ((NH 4 ) 2 SO 4 ). A strong correlation among the concentrations of SO 2 , NH 3 , and H 2 O was observed, and factor analysis shows that these concentrations are dominated by a common factor. It was also found that a mass quantity of NH 4 + and SO 3 2- existed in the condensate water of the flue gas. The TG-MS analysis shows that (NH 4 ) 2 SO 3 could be decomposed at 94.1 °C, and NH 3 , SO 2 , and H 2 O are released as reaction products in the form of gas. Therefore, a part of the NH 3 and SO 2 obtained by Fourier transform infrared spectroscopy (FTIR) monitoring may be derived from the decomposition of (NH 4 ) 2 SO 3 in the flue gas due to the high temperature during the sampling process, which was also confirmed in a lab experiment. The hot and wet sampling process will lead to overestimation of NH 3 and SO 2 emissions rather than FTIR method itself when monitoring the high-humidity FCC flue gas. Thus, the concentration of H 2 O in the flue gas and the type of sampling process need to be taken into consideration during the monitoring process., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Humic acid (HA) and water play an important role in polycyclic aromatic hydrocarbons (PAHs) adsorption and biodegradation in soil. In this work, molecular dynamics (MD) and electrostatic potential surfaces (EPSs) simulations are conducted to research the contribution of quartz surface, leonardite humic acid (LHA), and water to PAH adsorption. The adsorption energies between PAHs and LHA are much higher than that between PAHs and quartz. Simulation shows that the hydroxyl and carboxyl groups' attraction by LHA is the main adsorption force between PAHs and LHA. The π-π interaction between PAHs and LHA also contributes to the adsorption process. In addition, the mobility of water on quartz surface is much higher than that of LHA. Water should be regarded as an adsorbate in the system as well as PAHs. However, the presence of water has a remarkable negative effect on the adsorption of PAHs on LHA and quartz. The bridging effect of water could only enhance the stability of the aggregation system. The adsorption contribution of quartz and LHA to PAHs in the soil model tends to 0 if the water layer reaches 2.0 nm. Graphical abstract.