Grantee Research Project Results
2007 Progress Report: Sensitivity of Heterogeneous Atmospheric Mercury Processes to Climate Change
EPA Grant Number: R833375Title: Sensitivity of Heterogeneous Atmospheric Mercury Processes to Climate Change
Investigators: Schauer, James J. , Griffin, Robert J. , Shafer, Martin M. , Holloway, Tracey
Institution: University of Wisconsin - Madison
Current Institution: University of Wisconsin - Madison , University of New Hampshire
EPA Project Officer: Chung, Serena
Project Period: February 15, 2007 through February 14, 2010 (Extended to February 14, 2011)
Project Period Covered by this Report: February 15, 2007 through February 14, 2008
Project Amount: $899,731
RFA: Consequences of Global Change For Air Quality (2006) RFA Text | Recipients Lists
Research Category: Climate Change , Air
Objective:
The overall goal of the proposed project is to quantify the impact of climate change on key atmospheric processes that control the fate of mercury during transport from emission to deposition. Efforts are being directed at building on the existing scientific understanding of atmospheric mercury processes by examining the incremental impact of climate change variables on heterogeneous atmospheric mercury oxidation and depositional processes.
The goal is being realized by achieving the following objectives:
- Quantification of the sensitivity of dry deposition of elemental mercury, reactive gaseous mercury and particulate mercury to temperature, humidity, ozone, nitrogen oxides, and sunlight intensity
- Quantification of the sensitivity of atmospheric mercury oxidation and reduction reactions in fog and cloud water to temperature, sunlight intensity, and the composition of these atmospheric waters
- Investigation of the oxidation of elemental mercury in the presence of the complex atmospheric reactions that produce photochemical smog and secondary organic aerosols
- Investigation of the sensitivity of mercury deposition to climate change variables using a regional chemical transport model that will be evaluated using a year long data set of hourly speciated atmospheric mercury and event based wet deposition data
These efforts are providing a better understanding of impact of climate change on atmospheric mercury processes, supporting the development of strategies to control mercury deposition in the present and future. These results will also help understand the broader impact of climate change.
Progress Summary:
Year 1 of the project has focused on performing experimental development work and conducting initial studies to test and optimize experimental designs. Such work has been progressing in the following four areas, as defined in the initial proposal:
- Studies of mercury cycling to plants, soils, and other environmental surfaces at the UW-Madison Biotron controlled environment facility using on-line mercury instruments and mercury isotope spiking studies.
- Smog chamber studies of mercury oxidation during controlled ozone and SOA formation studies using expertise at the University of New Hampshire
- Laboratory studies of the chemical transformations of mercury with cloud and fog water collected using ultra-clean sampling methods along with parallel studies using artificial cloud and fog waters
- Regional chemical transport modeling to study atmospheric mercury deposition sensitivity to temperature, precipitation, and atmospheric circulation patterns associated with climate change
Mercury cycling to plants, soils, and environmental surfaces
Atmospheric deposition is the primary pathway by which mercury enters aquatic environments in which bacterial methylation and subsequent accumulation in the food chain can occur. The purpose of this module is to comprehensively determine the climate sensitivity of dry atmospheric deposition velocities for gaseous elemental mercury (GEM) and reactive mercury (RM) to a range of environmental surfaces. This is being done by determining the functional dependencies of these deposition velocities on temperature, light irradiance, and relative humidity which will be employed in the atmospheric modeling portion of the project described below. Various plants, soils, and environmental surfaces have been exposed to gaseous elemental mercury enriched in stable isotope 198 (GEM-198), in a controlled environment room at the UW-Biotron facility. Plots of two types of locally collected soil, peat, sand, concrete, asphalt, deciduous trees, and conifer trees were placed in the room along side a water surface sampler1, 2, and deposition coupons made from quartz fiber filters, some with absorbent coatings. GEM-198 was introduced into the room continuously at an elevated concentration over the course of 7 days at two ambient temperatures (10°C and 30°C) under a summer light condition. The objective of these initial experiments was to evaluate the ability of the experimental design we have adopted to successfully capture the uptake of GEM-198, by the aforementioned surfaces. These experiments have largely been completed, and analysis of these samples was in progress at the time of writing. Our intent is to optimize these experiments in response to our initial results and achieve significant progress in making further measurements during the coming summer.
Smog chamber photo-oxidation of GEM in the presence of photochemical smog and secondary organic aerosols
GEM is most effectively transferred from the atmosphere to aquatic ecosystems by wet and dry deposition after oxidation to reactive mercury. The oxidation of GEM by oxidants such as ozone, OH, and various halogen species have previously only been studied in homogeneous reactions systems3-15, which do not effectively represent the heterogeneous aerosol reaction systems that are present in the environment. This module aims to evaluate heterogeneous reaction rates of GEM of a range of oxidation reactions. This is being achieved by observing the effect of a complex smog reaction system that leads to the formation of secondary organic aerosol on reaction rate kinetics for oxidants such as ozone and OH. The effect of the updated reaction kinetics data on dry and wet deposition rates will be studied in the climate sensitivity modeling portion of the project described below. During August 2007 two weeks of initial experiments were conducted in the smog chamber at the University of New Hampshire, to test the experimental design for feasibility and potential pitfalls. GEM-198 was added to ongoing oxidations of 1-methylnaphthalene by OH under ultraviolet lamps. Concentrations of GEM were monitored real-time using a Tekran 2537A GEM analyzer, and GEM oxidized to reactive mercury (RM) was collected on specially prepared filter substrates16. The experiments successfully demonstrated that GEM-198 could be introduced into the chamber and photochemically oxidized to reactive mercury (RM), which was successfully collected and analyzed by mercury thermal desorption analysis. Isotopic analyses of these samples are ongoing. The experiments highlighted the necessity to analyze the exposed filter substrates at UNH shortly after collection. These experiments have provided the necessary basis to allow success in the final round of experiments that will be performed at UNH during July and August, 2008.
Climate sensitivity of atmospheric mercury red-ox reactions in fog and cloud water surrogates.
Although mercury in wet deposition has been extensively studied17, 18, the direct and indirect effects of climate change on the speciation and therefore fate of deposited mercury in a receptor are not well understood. The climate sensitivity of mercury speciation in fog and cloud water will be assessed by exposing mercury spiked rainwater and synthetic fog and cloud water to a range of temperature and light conditions in combination with chemical adjustments to represent indirect effects of climate change on fog and cloud water chemistry. Rain water and total suspended particulate matter (TSP) collections (for making synthetic fog and cloud water) have been in progress at Devil’s Lake State Park, WI for nearly 1 year. We have in hand approximately 10 liters of rainwater from summer and spring collections, and TSP samples collected during summer, winter and spring. Sample collections will continue during the coming summer and fall, to ensure sufficient season coverage and sample volume for experiments.
Considerable development work has been conducted in the treatment and analysis methods for the surrogate fog and cloud water solutions. Teflon sparges have been chosen as reactor vessels for the experiments, in which surrogate cloud water solutions are exposed to a range of temperature and light conditions in a UW Biotron controlled environment room. Sample solutions are spiked with GEM vapor, reactive mercury (Hg(NO3)2), to facilitate observations in the change of chemical speciation, and chemical adjustments are made to mimic indirect effects of climate change, such as the incremental increase in coal-fired power generation. EPA Method 1631 revision E has been modified to allow the pre and post experimental analysis of the samples: GEM and RM concentrations are differentiated by the addition of an initial sparge step to extract GEM from the sample solution before the addition of BrCl, overnight heating, and analysis for the remaining reactive mercury by a standard EPA 1631E protocol.
Initial experiments have focused on verifying the ability to recover standard additions of GEM and RM made to sparges containing MilliQ water which are then sealed for environmental exposure. Recoveries have been acceptable from samples left in the laboratory overnight, but variable recoveries have been reported for samples transported to and from the UW-Biotron (other side of campus). We anticipate a quick solution to this problem, and expect to make significant progress with these experiments this summer.
Atmospheric mercury modeling to study sensitivities of mercury deposition to temperature, precipitation, and atmospheric circulation patterns associated with climate change
In this first year of the project, the modeling group has completed key steps toward analysis and development of the CMAQ-Hg model. Preliminary simulations have been performed for July 2002, building on 2002 CMAQ analysis (performed under EPA STAR Grant #R831840). Through the development of these simulations, we have succeeded in compiling CMAQ-Hg on our Mac OSX modeling platform, processed the 2001 emissions inventory developed in support of the Clean Air Mercury Rule, CAMR (building on the 1999 National Emissions Inventory) through the SMOKE model, and run CMAQ for the July 2002 test month. Initially, we had planned to use speciated mercury emissions from the 2002 National Emissions Inventory, but through testing with SMOKE, we have identified errors in this inventory distribution, which have since been reported to Marc Houyoux at the U.S. EPA.
To test the quality of these test simulations, we are comparing with analogous studies, including reports to inform CAMR, results from Dr. J. Lin's group at Lamar University, deposition data from the EPA Mercury Deposition Network, and other studies in the published literature. Following full quality assurance of our modeling system, we will perform 12 km x 12 km simulations over the Upper Midwest for 2003 and 2004 to compare with ambient measurements taken over Devil's Lake and Milwaukee, Wisconsin. Meteorology for these upcoming runs will be taken from the Weather Research and Forecasting (WRF) model.
Future Activities:
Primary objectives for the coming year are to finish method development and move into a period of experiment optimization, data collection, and model implementation to allow for the publication of at least one or more papers from each module by early in the third year of the project.
References:
- Sakata, M.; Marumoto, K., A new method for evaluating dry deposition of mercury using a water surface sampler. Journal De Physique Iv 2003, 107, 1177-1180.
- Sakata, M.; Marumoto, K., Dry deposition fluxes and deposition velocities of trace metals in the Tokyo metropolitan area measured with a water surface sampler. Environmental Science & Technology 2004, 38, (7), 2190-2197.
- Ariya, P. A.; Khalizov, A.; Gidas, A., Reactions of gaseous mercury with atomic and molecular halogens: Kinetics, product studies, and atmospheric implications. Journal of Physical Chemistry A 2002, 106, (32), 7310-7320.
- Ariya, P. A.; Ryzhkov, A., Atmospheric transoformation of elemental mercury upon reactions with halogens. Journal De Physique Iv 2003, 107, 57-59.
- Calvert, J. G.; Lindberg, S. E., Mechanisms of mercury removal by O-3 and OH in the atmosphere. Atmospheric Environment 2005, 39, (18), 3355-3367.
- Hall, B., THE GAS-PHASE OXIDATION OF ELEMENTAL MERCURY BY OZONE. Water Air and Soil Pollution 1995, 80, (1-4), 301-315.
- Hall, B.; Schager, P.; Ljungstrom, E., AN EXPERIMENTAL-STUDY ON THE RATE OF REACTION BETWEEN MERCURY-VAPOR AND GASEOUS NITROGEN-DIOXIDE. Water Air and Soil Pollution 1995, 81, (1-2), 121-134.
- Pal, B.; Ariya, P. A., Gas-phase HO center dot-Initiated reactions of elemental mercury: Kinetics, product studies, and atmospheric implications. Environmental Science & Technology 2004, 38, (21), 5555-5566.
- Pal, B.; Ariya, P. A., Studies of ozone initiated reactions of gaseous mercury: kinetics, product studies, and atmospheric implications. Physical Chemistry Chemical Physics 2004, 6, (3), 572-579.
- P'yankov, V. A., O kinetike reaktsii parov rtuti s ozonom (Kinetics of the reaction of mercury vapour with ozone). . Zhurmal Obscej Chemii Akatemijaneuk SSSR 1949., 19, pp. 224–229.
- Raofie, F.; Ariya, P. A., Kinetics and products study of the reaction of BrO radicals with gaseous mercury. Journal De Physique Iv 2003, 107, 1119-1121.
- Raofie, F.; Ariya, P. A., Product study of the gas-phase BrO-initiated oxidation of Hg-0: evidence for stable Hg1+ compounds. Environmental Science & Technology 2004, 38, (16), 4319-4326.
- Sommar, J.; Hallquist, M.; Ljungstrom, E., Rate of reaction between the nitrate radical and dimethyl mercury in the gas phase. Chemical Physics Letters 1996, 257, (5-6), 434-438.
- Sommar, J.; Hallquist, M.; Ljungstrom, E.; Lindqvist, O., On the gas phase reactions between volatile biogenic mercury species and the nitrate radical. Journal of Atmospheric Chemistry 1997, 27, (3), 233-247.
- Tokos, J. J. S.; Hall, B.; Calhoun, J. A.; Prestbo, E. M., Homogeneous gas-phase reaction of Hg-0 with H2O2, O-3, CH3I, and (CH3)(2)S: Implications for atmospheric Hg cycling. Atmospheric Environment 1998, 32, (5), 823-827.
- Rutter, A. P.; Hanford, K. L.; Zwers, J. T.; Perillo-Nicholas, A. L.; Schauer, J. J.; Worley, C. A.; Olson, M. L.; DeWild, J. F., Evaluation of an Off-line Method for the Analysis OF Atmospheric Reactive Gaseous Mercury and Particulate Mercury. In Press by the Journal of Air and Waste Management Association 2007.
- Lin, C. J.; Pehkonen, S. O., The chemistry of atmospheric mercury: a review. Atmospheric Environment 1999, 33, (13), 2067-2079.
- Lin, C. J.; Pongprueksa, P.; Lindberg, S. E.; Pehkonen, S. O.; Byun, D.; Jang, C., Scientific uncertainties in atmospheric mercury models I: Model science evaluation. Atmospheric Environment 2006, 40, (16), 2911-2928.
Journal Articles:
No journal articles submitted with this report: View all 4 publications for this projectSupplemental Keywords:
Aerosol, mercury speciation,, RFA, Air, climate change, environmental monitoringProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.