Optically levitated single droplet study of the sea spray aerosol that contains the mercuric halides

Mercury exists in the atmosphere in three major forms: gaseous elemental mercury, gaseous oxidized mercury, and particulate-bound mercury. Among these three forms, the gaseous-phase mercury takes up more than 90% and has been well studied. However, the particulate-bound mercury that is mainly related to the heterogeneous surface, such as aerosols, air-water interfaces, etc., has been less investigated. This is mainly due to the complex nature of heterogeneous chemistry and the experimental difficulties in making accurate measurements.

Optical trapping was demonstrated that can be used to simulate the real atmospheric environment of a single aerosol particle in air. In this study, we used optical trapping-Raman spectroscopy to study the single droplet of the sea spray aerosol that contains Hg(II) halides (HgX₂, X=Cl, Br). The single droplets were trapped in air under different conditions (exposure to ozone or UV radiation) with different relative humidities (RH). The results were analyzed by the single particle-Raman spectra. We discussed the results in (1) The equilibrium process and hygroscopic properties of the sea spray aerosol; (2) The chemical reaction that happens between ozone and Hg(II) halides in sea spray aerosol in the single particle level; (3) The influence of the UV radiation on the Hg(II) halides in sea spray aerosol.