Effect of methyl hydrogen sulfate on the formation of sulfuric acid‐ammonia clusters: A theoretical study

Abstract Methyl hydrogen sulfate (MHS) as a common nucleation precursor that has important effect on new particle formation (NPF). Liu et al. showed that MHS and sulfuric acid (SA) generation are competitive due to consumption of the common precursor SO 3 , and the nucleation ability of SA is better than MHS. Thus, MHS inhibits the SA‐DMA‐based clusters formation particularly in regions with high [MO] (methanol) (Liu et al., Proc. Natl. Acad. Sci. U.S.A. 2019, 116 , 24,966). However, in regions where [H 2 O] is much higher than [MO] ([SA] > > [MHS]), the SO 3 consumed by the generation of less MHS will not significantly reduce the [SA], whether MHS still inhibits SA‐A‐based clusters formation and how MHS affects the growth pathways of MHS‐SA‐A‐based clusters remains unclear. Hence, quantum chemistry calculations combining Atmospheric Cluster Dynamics Code (ACDC) are used to investigate the role of MHS in the SA‐A‐based system. Our conclusions show two different effects of MHS in NPF process: “inhibiting” in regions with high [MO] and “weakly facilitating” in regions with high [H 2 O] and low [MO]. The growth pathways show that with the increasing [MHS], the role of MHS in NPF gradually changes from “transporter” to “participator”, and the contribution to the pathways increases from 7 to 85%. Our results contribute to understanding the NPF in low‐temperature regions with different concentrations of MO and H 2 O.