Study of surface and heterogeneous chemistry of mercury using a single-particle approach
Abstract
The overarching goal of this project is to systematically understand the mercury (Hg) surface and heterogeneous chemistry at atmospheric relevant surfaces. Extensive effort has been paid to the study of the gas phase mercury chemistry, yet very limited attempt has been made to understand the heterogeneous mercury chemistry which involves reactions (oxidation and reduction) and equilibrium processes (adsorption and desorption) at atmospherically relevant surfaces. Aerosols (solid particles or droplets) are major heterogeneous components in the atmosphere, which provide sufficient surfaces for heterogeneous reactions and interfacial processes. Numerous observations suggest that heterogeneous surfaces play a key role in mercury chemistry; however, there is little known about mercury reactions and equilibrium processes at the surfaces. As such, the heterogeneous chemistry in the current atmospheric models is either entirely ignored or poorly described. This insufficient knowledge of mercury interactions with various surfaces constitutes one of the major gaps in mercury chemistry. We propose to study mercury heterogeneous oxidation/reduction and equilibrium processes (adsorption and desorption) at atmospheric relevant surfaces using a novel optical trapping single-particle technology. More specifically, we will use single optically levitated aerosol solid particles or droplets as a well-defined single-particle reactor (SPR) to investigate mercury redox reactions and equilibrium process at the particle surface under controlled reaction environments. There are four research objectives: (1) Build the SPR using a universal optical trap that integrates both Raman and cavity ringdown spectroscopy, imaging, chemical introduction, and sensor and control portions. (2) Understand heterogeneous reactions on the surfaces of various aerosol particles in terms of uptake coefficient, reaction rates with atmospheric radicals (OH, O3, NO3, Br, etc.) under controlled environments (reactantÕs concentration, relative humidity, pH value, and temperature). (3) Investigate effects of particleÕs surface properties (constituents, size, hygroscopicity, etc.) on oxidation, reduction, adsorption, and desorption processes. (4) Investigate mercury partition and photoreduction processes using single droplets under light radiation. The novelty of the proposed work is threefold. (1) A systematic study of surface and heterogeneous chemistry of atmospheric mercury is limited or none. (2) Using a single aerosol particle levitated in air by the light force as an SPR to study mercury surface chemistry is a new approach which has not been reported to date. The novel SPR idea is built upon the most recent demonstration of the study of chemical reactions on single trapped particles. The single-particle approach proposed in this work offers particle samples to be close to their native state (atmospheric aerosol state) which has no surface interferences and the wall effect. (3) Change of mercury compounds and reaction intermediates and products is directly monitored using a suite of advanced laser spectroscopy and imaging techniques that are integrated into the SPR. These direct and time-dependent measurements will provide more accurate data. Experimental data and parameters will be adopted by modelers in future model studies to reduce uncertainties in current atmospheric Hg models. Results will help fill in the knowledge gap in the atmospheric Hg heterogeneous and surface chemistry that is virtually unexploited to date. The SPR technique developed in this project is technologically transformative and can be applied to the study of other surface and heterogeneous chemistry. Two students will be involved in the proposed research activities. They can be potentially future workforce in the US Department of Defense. The project will also further strengthen the PIÕs long-lasting collaboration with scientists at Army Research Laboratory.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jun 25, 2021
- Source ID
- W911NF2110171
Entities
People
- Chuji Wang
Organizations
- Army Contracting Command
- Mississippi State University
- United States Army