A novel formation mechanism of NH₂SO₃H and its enhancing effect on methanesulfonic acid-methylamine aerosol particle formation in agriculture-developed and coastal industrial areas

Abstract. Sulfamic acid (SFA) significantly impacts atmospheric pollution and poses potential risks to human health. Although traditional source of SFA and its role on sulfuric acid-dimethylamine new particle formation (NPF) has received increasing attention, the formation mechanism of SFA from HNSO₂ hydrolysis with CH₃SO₃H and its enhancing effect on methanesulfonic acid-methylamine APF has not been studied, which will limit the understanding for the source and loss of SFA in agriculture-developed and coastal industrial areas. Here, the gaseous and interfacial formation of SFA from HNSO₂ hydrolysis with CH₃SO₃H was investigated using quantum chemical calculations and BOMD simulations. Furthermore, the role of SFA in CH₃SO₃H-CH₃NH₂ system was assessed using the Atmospheric Cluster Dynamics Code kinetic model. Our simulation results indicate that the gaseous SFA formation from the hydrolysis of HNSO₂ with CH₃SO₃H can be competitive with that catalyzed by H₂O within an altitude of 5–15 km. At the air-water interface, two types of reactions, the ions forming mechanism and the proton exchange mechanism to form NH₂SO₃^-•••H₃O⁺ ion pair were observed on the timescale of picosecond. Considering the overall environment of sulfuric acid emission reduction, the present findings suggest that SFA may play a significant role in NPF and the growth of aerosol particle as i) SFA can directly participate in the formation of CH₃SO₃H-CH₃NH₂-based cluster and enhance the rate of NPF from these clusters by approximately 10³ times at 278.15 K; and ii) the NH₂SO₃^- species at the air-water interface can attract gaseous molecules to the aqueous surface, and thus promote particle growth.