The role of hydroxymethanesulfonic acid in the initial stage of new particle formation

Organosulfur compounds are being of increasing interest in the atmospheric environment and climate because of their profound impacts on the formation of secondary organic aerosol. However, their role in the initial step of new particle formation (NPF) is still unclear. Here, using Density Functional Theory (DFT) calculation combined with the Atmospheric Clusters Dynamic Code (ACDC) model, we study the enhancement effect of hydroxymethanesulfonic acid (HMSA) - one of the most important organosulfur compounds - on sulfuric acid (SA) - dimethylamine (DMA) molecular clustering and the underlying mechanism. The results show that HMSA can enhance cluster formation rates at room temperature with the enhancement strength ranging from zero to four orders of magnitude. The comparison of the enhancement effect between HMSA and MSA shows that the enhancement strength of HMSA could be up to 3.97 times stronger than that of MSA, indicating that HMSA may be a more potential stabilizer. Meanwhile, different from the “bridge” role of α-hydroxyl acids, HMSA acts as “stabilizer” directly participating in NPF. Both of its enhancement strength on cluster formation rate and the corresponding contribution to the growth pathway present a negative dependence on SA concentration. All those could, to some extent, help to explain the missing sources of NPF between field observation and currently cognition, as well as to assist us to better understand atmospheric organosulfur chemistry.