Ammonium nitrate promotes sulfate formation through uptake kinetic regime

Abstract. Although the anthropogenic emissions of SO2 have decreased significantly in China, decrease SO42- PM2.5 is much smaller than that SO2. This implies an enhanced formation rate ambient air, and mechanism still under debate. work investigated particulate sulfate based on statistical analysis long-term observations Shijiazhuang Beijing supported with flow tube experiments. Our main finding was sulfur oxidation ratio (SOR) exponentially correlated RH (SOR = 0.15+0.0032×exp⁡(RH/16.2)) -0.045+0.12×exp⁡(RH/37.8)). In Shijiazhuang, SOR linearly aerosol water content (AWC) 0.15+0.40×AWC/PM2.5). results suggest uptake instead S(IV) particle phase rate-determining step for formation. NH4NO3 plays important role AWC change state, which a crucial factor determining kinetics during haze days. show NH3 promoted subsequently SOR, while NO2 had little influence presence NH3.