Scrambling of Molecular Speciation of Gaseous Oxidized Mercury via Surface Reactions on Atmospheric Aerosols
ALEXEI KHALIZOV, Na Mao,
New Jersey Institute of Technology Abstract Number: 354
Working Group: Aerosol Chemistry
AbstractMercury enters the aquatic and terrestrial environments primarily via the deposition of atmospheric gaseous oxidized mercury, Hg(II). The original Hg(II) is produced by photochemical oxidation of elemental gaseous mercury and our knowledge of its molecular composition is limited, coming primarily from quantum chemical calculations. Atmospheric aerosols represent a significant sink for Hg(II) and there is a possibility that the reactions on/in aerosol particles may lead to changes in the molecular speciation of Hg(II).
We investigated interactions of a series of Hg(II) compounds with each other and with other chemicals under conditions that simulate the processing of Hg(II) by atmospheric aerosols. The reactions were studied in aqueous solutions and on surfaces, and the products were analyzed in the gas phase (by ion drift - chemical ionization mass spectrometry), in solution (by electrospray ionization - mass spectrometry), and on surface (by Raman microscopy). In most cases, we observed a rapid formation of Hg(II) exchange products, which readily volatilized into gas phase at room temperature. We propose that a similar gas-particle exchange reactions may occur in the atmosphere, where the original Hg(II) species (e.g., BrHgONO and HOHgOOH) would react with each other and with particle constituents to form different Hg(II) substances. For instance, a readily volatilizable HgCl
2 can be produced through the exchange of the originally low-volatility Hg(II) with the particle-phase chloride. The occurrence of such exchange reactions can scramble the original molecular speciation of Hg(II) on a time scale from hours to a day, affecting our ability to predict the transport and deposition of atmospheric mercury, as well its further transformations and bioaccumulation in the aquatic and terrestrial environments.