2005 Progress Report: Models and Measurements for Investigating Atmospheric Transport and Photochemistry of Hg

EPA Grant Number: R829799
Title: Models and Measurements for Investigating Atmospheric Transport and Photochemistry of Hg
Investigators: Keeler, Gerald J. , Sillman, Sanford
Institution: University of Michigan
EPA Project Officer: Chung, Serena
Project Period: November 1, 2002 through October 31, 2005 (Extended to October 31, 2006)
Project Period Covered by this Report: November 1, 2004 through October 31, 2005
Project Amount: $899,597
RFA: Mercury: Transport, Transportation, and Fate in the Atmosphere (2001) RFA Text |  Recipients Lists
Research Category: Mercury , Air Quality and Air Toxics , Safer Chemicals , Air

Objective:

The objective of the research project is to develop a 3-dimensional Eulerian model for transport and photochemistry of mercury, including fully integrated gas-phase, aqueous, and aerosol chemistry. The project also seeks to develop detailed comparisons between model results and measurements from two field campaigns: a recently completed field campaign in south Florida and a campaign currently being planned for the upper Midwest.

The project also seeks to use model results to investigate several research issues related to mercury: (1) the impact of local emissions relative to transport from distant sources; (2) the impact of photochemical processes; and (3) the relative importance of cloud chemistry on the transformation, transport, and deposition of mercury. A major objective will be to identify measurements that might provide evidence relevant to these issues.

Progress Summary:

During Year 1 and Year 2 of the project, a modified version of the Community Model for Air Quality (CMAQ) was developed that included emissions, photochemistry, transport, and deposition of elemental and reactive gaseous mercury (RGM). The modified CMAQ included an integrated solution for combined gas-phase and aqueous chemistry, in place of the original CMAQ procedures that solve for gas-phase and aqueous chemistry separately. The integrated solver accounts for interactions between gas-phase and aqueous chemistry on short time scales (<1 second) and also allows for a much more detailed representation of aqueous chemistry. Emissions of mercury were added, derived from the U.S. Environmental Protection Agency’s 1999 Hazardous Air Pollutants (HAP) Inventory version 3. During Year 2, the model gas and aqueous chemistry was expanded to include chlorine and bromine chemistry, in addition to the gas and aqueous chemistry of mercury, sulfur, and ozone and related species.

During Years 2 and 3 of the project, the model was used to simulate conditions for 11 days in June 2000, for a model domain that included the eastern half of the United States and the western half of the Atlantic Ocean (from 55 to 105° W longitude). The goal of the simulation was to assess the photochemical formation of reactive mercury at the regional scale, including photochemical evolution over 5 days or longer. The selected time period also coincided with a series of aircraft measurements in south Florida.

The model predicted that high ambient concentrations of RGM (up to 200 pg m-3) can be formed through photochemical conversion of Hg0 to RGM. The high RGM was predicted to be episodic in nature, with the highest RGM coinciding with extended cloud-free periods. Elevated RGM is not limited to source regions (such as the Eastern United States) and can form over the Atlantic Ocean as well (see Figure 1).

Figure 1. Concentrations of Hg(II) (pg m(-3)) in the Model at 3000 m Altitude for the Full Model Horizontal Domain

Figure 1. Concentrations of Hg(II) (pg m-3) in the Model at 3000 m Altitude for the Full Model Horizontal Domain. Results are for 5:00 p.m., June 14, 2000. The colors represent the following concentration intervals: grey, 0-40 pg m-3; dark blue, 40-80 pg m-3; light blue, 80-120 pg m-3; green, 120-160 pg m-3; light green, 160-200 pg m-3; orange, 200-240 pg m-3; and red, 240-280 pg m-3.

A comparison with aircraft measurements in south Florida (Figure 2) shows that the model reproduces several observed features. RGM increases with elevation (up to 3000 m) in both the measurements and the model. Measured RGM shows intermittent high RGM with concentrations up to 250 pg m-3. Although the highest measured RGM was twice as high as the model value in south Florida, the model did predict up to 240 pg m-3 in nearby regions of the Atlantic Ocean.

Figure 2. Measured Hg(II) (pg m(-3)) Versus Altitude (km) From Aircraft Measurements Over South Florida and the Adjacent Atlantic Ocean During June, 2000 (points)

Figure 2. Measured Hg(II) (pg m-3) Versus Altitude (km) From Aircraft Measurements Over South Florida and the Adjacent Atlantic Ocean During June, 2000 (points). The line represents model Hg(II) versus altitude, based on an average of model results during the afternoon on the five days (June 9, 12, 14, 25, and 26) that coincide with measurements.

Tests have been completed for model sensitivity to direct emissions, background Hg0, and chemistry, including tests for the impact of a specific reaction (the aqueous reaction of Hg(II) with HO2) that was recently found to be uncertain.

It was found that ozone formation during pollution events can significantly affect ambient RGM. The model predicts a 50 percent reduction in RGM if emission of ozone precursor emissions were eliminated. The model predicted that RGM should show a significant positive correlation with ozone in cases where RGM is enhanced due to ozone formation. This correlation should provide a way to test for the validity of the model prediction concerning the impact of ozone on RGM.

Future Activities:

Results of the project will be submitted for publication in a peer-reviewed journal. An article currently is in preparation. We expect to submit the article within 3 months of the end of the project.

Journal Articles:

No journal articles submitted with this report: View all 2 publications for this project

Supplemental Keywords:

reactive mercury, RGM, ozone, chlorine, bromine,, RFA, Scientific Discipline, Air, INTERNATIONAL COOPERATION, Waste, Ecosystem Protection/Environmental Exposure & Risk, POLLUTANTS/TOXICS, Air Quality, air toxics, Environmental Chemistry, Chemicals, climate change, Air Pollution Effects, Fate & Transport, Environmental Monitoring, Atmospheric Sciences, Chemistry and Materials Science, Atmosphere, fate and transport, air pollutants, mercury, Hg, mercury emissions, modeling, photochemistry, mercury cycling, Eulerian model, chemical kinetics, aerosol, atmospheric mercury chemistry, mercury chemistry, atmospheric chemistry, atmospheric deposition, heavy metals, mercury vapor, contaminant transport models, atmospheric mercury cycling

Relevant Websites:

http://www.sph.umich.edu/ehs/umaql Exit
http://www-personal.engin.umich.edu/~sillman/ Exit

Progress and Final Reports:

Original Abstract
  • 2003 Progress Report
  • 2004 Progress Report
  • Final Report