1999 Progress Report: Light Induced Mercury Volatilization from Substrate Mechanism(s) Responsible and In situ OccurrenceEPA Grant Number: R825249
Title: Light Induced Mercury Volatilization from Substrate Mechanism(s) Responsible and In situ Occurrence
Investigators: Gustin, Mae Sexauer
Institution: University of Nevada - Reno
EPA Project Officer: Chung, Serena
Project Period: December 15, 1996 through December 14, 1999 (Extended to December 14, 2000)
Project Period Covered by this Report: December 15, 1998 through December 14, 1999
Project Amount: $288,645
RFA: Exploratory Research - Air Chemistry & Physics (1996) RFA Text | Recipients Lists
Research Category: Engineering and Environmental Chemistry , Air
Objective:The objectives of this project are to: (1) determine the mechanisms responsible for light-enhanced mercury volatilization from substrate using controlled laboratory experiments, (2) investigate the effect of ambient light conditions on in situ mercury flux using micrometeorological and field chamber techniques, and (3) develop a method for speciation of mercury in substrate. Mercury is designated a global pollutant because it exists as gaseous phases, which allows it to be transported long distances via the atmospheric pathway. Because of its propensity towards a gaseous phase, understanding the mechanisms that promote its movement from terrestrial landscapes to the atmosphere must be determined to assess the contribution of anthropogenic point sources relative to terrestrial nonpoint sources to the atmospheric mercury budget.
Progress Summary:Speciation of Mercury in Soil. To determine the mechanism responsible for light enhancement of mercury emissions, the form of mercury in the soil must be assessed. In addition, to assess the mobility and the bioavailability of mercury at contaminated sites, the speciation of mercury in substrate must be understood. In this project, we have focused on testing cited sequential extraction methods on characterized substrates, and on developing an extraction protocol for determining elemental mercury (Hgo), mercury chloride (HgCl2) representing a reactive Hg species, and the strongly bound fraction (Hgr) assumed to be primarily HgS in soils. In 1999, the focus was on developing the extraction protocol, and in 2000, this protocol will be tested on field samples with different characteristics. The results of our speciation protocol will be compared with speciation on the same samples using a pyrolytic method for determination of mercury species in soils, a sequential extraction procedure, and synchrotron radiation based X-ray absorption spectroscopy, respectively. Results of 1999 work demonstrate that sequential extraction methods, as applied, may not adequately determine specific mercury species in substrate and that sequential extraction efficiencies are highly dependent on the substrate composition.
Laboratory Chamber Investigation of Emissions. The laboratory chamber consists of a glass chamber constructed so that environmental variables impacting emissions are precisely controlled (Gustin, et al., 1997). Flux is determined with the following equation: F = (Co-Ci)/A * Q, where F is the flux in ng/m2h, Co and Ci are the mercury concentration measured at the chamber inlet and outlet, respectively, A is the area from which emissions are being measured and Q is the flow of air through the chamber. Studies in 1999 utilized an automated Tekran mercury analyzer that records changing air concentrations at the 10's of pg/m3 concentrations on 5-minute intervals. This allowed for designing experiments that would allow us to understand the light-enhancement mechanism as a function of time. The light-enhanced emissions is an immediate response to light and was observed with samples amended with HgS, not HgCl2 or samples amended with Hgo. Two hypotheses were developed in 1998 for the light enhancement mechanism: physical desorbtion of mercury due to the incident light energy or photoreduction of reactive mercury phases. Work will be done in the beginning of 2000 to finalize this component of the study.
In Situ Measurement of the Light Effect on Mercury Emissions. Two field methods were applied in 1999 to add to the field database developed that year, micrometeorological methods and field flux chambers. In 1999, field chamber and micrometeorological flux measurements were made at an anthropogenically Hg-contaminated site near Gold Hill, NV, within the Carson River Superfund site and the Steamboat Springs geothermal area south of Reno. Additional data focusing on light enhancement of emissions were collected using a field flux chamber at McLaughlin, CA, and Ivanhoe, NV. In the field, a variety of environmental factors influence emissions including, light, temperature, turbulence, substrate mercury concentration, vegetative cover, precipitation, etc. Determining the overall magnitude of influence of light-enhanced emissions is difficult to demonstrate with these other factors coming into play. However, data developed during 1999 demonstrate the significant influence of light on emissions and the rapid flux response to light in situ.
Future Activities:Completion and submission of the manuscripts listed above.
During CY2000 the sequential extraction speciation technique will be done on environmental samples and compared with other studies of mercury speciation in substrate.
A final series of experiments with the laboratory gas exchange chamber will be completed so that we may constrain the factors controlling light enhanced emissions.
Use of the developed method for determining mercury speciation in substrate on field samples.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
|Other project views:||All 10 publications||3 publications in selected types||All 3 journal articles|
||Gustin MS, Rasmussen P, Edwards G, Schroeder W, Kemp J. Application of a laboratory gas exchange chamber for assessment of in situ mercury emissions. Journal of Geophysical Research – Atmospheres 1999;104(D17):21,873-21,878.||
||Gustin MS. On the mechanism controlling the light enhancement of mercury emissions from substrate. Science of the Total Environment.||