The Influence of Clouds and the Marine Environment on Atmospheric Mercury Chemistry and CyclingEPA Grant Number: U915841
Title: The Influence of Clouds and the Marine Environment on Atmospheric Mercury Chemistry and Cycling
Investigators: Malcolm, Elizabeth G.
Institution: University of Michigan
EPA Project Officer: Michaud, Jayne
Project Period: December 1, 2000 through December 1, 2001
Project Amount: $95,448
RFA: STAR Graduate Fellowships (2000) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Air Quality and Air Toxics , Fellowship - Atmospheric Sciences
The objective of this research project is to investigate the effect of clouds and the marine environment on mercury (Hg) chemistry, speciation, and cycling.
To gain a more complete understanding of the atmospheric Hg cycle, direct measurements will be performed during two separate field campaigns. The first study, in Vermont, investigates the role of clouds in the atmospheric Hg cycle. The second, in south Florida, investigates Hg chemistry in the coastal environment. Results of these field campaigns will be combined with modeling of Hg chemistry, transport, dispersion, and deposition. Non-precipitating clouds will be sampled on Mt. Mansfield, Vermont, using a collector that was designed and evaluated specifically for Hg sampling. During the same time period, precipitation, elemental vapor phase mercury (Hg0 (g)), and particulate mercury (Hg (p)) will be sampled at a lower elevation site. Cloud and rain samples will be analyzed for trace elements (e.g., Ni, Cu, Zn, As, Sr, Cd, Sb, Pb) by inductively coupled plasma mass spectroscopy (ICP-MS) and cold vapor atomic fluorescence (Hg). Meteorological analysis and trace metal data will identify Hg source regions influencing cloud Hg concentrations. The Florida research is designed to gain a better understanding of Hg chemistry by making detailed measurements of Hg species and other atmospheric species expected to react with Hg under "clean" marine conditions, and under anthropogenically influenced (incinerators, power plants) conditions. Hg measurements include Hg0(g) and Hg2+(g), and Hgp in two size ranges, <2.5 m and <10 m. Additional measurements include SO2, O3, HNO3, HCl, HONO, HNO3, NH3, acid aerosols, particulate trace elements, and aerosol carbon. Results will be further investigated using EPA's Models-3/Community Multiscale Air Quality Model modified by the University of Michigan (UM) to include Hg chemistry and deposition. The UM modified model includes both gaseous and aqueous phase chemistry, as well as modules for source emissions, transport, mass transfer, precipitation processes, and wet and dry deposition. The model analysis utilizes meteorological input necessary to capture mesoscale meteorology features such as local land-sea breeze dynamics, which strongly influence the ambient Hg concentrations.
The transformation of Hg has been hypothesized to occur via two processes: (1) aqueous chemistry after incorporation into cloud drops, and (2) by reaction with gaseous or particulate halogens in the marine environment. To date, few field studies have been performed to investigate these hypotheses. Over the past 20 years, Hg-contaminated fish in remote lakes worldwide often have been linked to atmospheric deposition of Hg transported from sources hundreds of kilometers away. Understanding the sources, atmospheric transport, chemistry, and deposition of Hg is crucial to finding a solution to this problem.