Ion pair particles at the air–water interface

Significance According to our Born–Oppenheimer molecular dynamics simulations, the ion pair particle formation from the hydrogen-bonded complex between methanesulfonic acid (HMSA) and ammonia/amines on the water droplet surface is observed within a few femtoseconds of the simulation time. This suggests a mechanism for the gas to particle conversion at the air–water interface. These results may help in understanding the aerosol particle formation in the remote marine atmosphere, particularly in polar regions, where the concentration of HMSA in the smallest particles was similar to that of nonsea salt sulfate and the mechanism of the particle formation remains unclear.