The Atmospheric Fate and Transport of Mercury

1
The Atmospheric Fate and Transport of Mercury
Mark Cohen NOAA Air Resources Laboratory Silver
Spring, Maryland
Presentation to the Chesapeake Bay Toxics
Subcommittee Meeting June 12, 2002 Annapolis,
Maryland
2
(No Transcript)
3
(No Transcript)
4
(No Transcript)
5
Typical, average travel distance in the
atmosphere is roughly 400 km per day
1- ,3- , and 5-day back-trajectories from the
Great Lakes
6
Atmospheric monitoring can tell you the
concentration of a compound is at a given
location at a given time for a given media (air,
precipitation, soil, surface water, etc.), but

• How representative are the measurements
• with respect to spatial and temporal
  variations?
• What are the reasons for variations among samples
  at a given site, or between samples at different
  sites?
• What are the main sources contributing to each
  observed measurement?

7

• We are generally not actually interested in the
  concentration or deposition at a single
  monitoring site

• We are interested in the deposition to an entire
  water body, or to a particular ecosystem

• We are just using the few monitoring sites that
  we might have to give us a clue as to what the
  total impact might be

8
you cant get all the answers you need from
monitoring alone!
9
Emissions
Meteorology
Atmospheric Fate processes (V/P, rxns, wet/dry
deposition)
Evaluation of the model using ambient measurements
Model Results
10
Information obtained by monitoring cannot be
fully utilized without modeling
AND Modeling cannot be done credibly without
using monitoring to ground-truth the results
11
The Role and Potential Value of Models
1. Models are mathematical and/or conceptual
descriptions of real-world phenomena

• They are necessarily a simplification the real
  world is very complicated
• Hopefully the most important aspects are treated
  sufficiently well

12
The Role and Potential Value of Models
2. Models are potentially valuable for

• Examining large-scale scenarios that cannot
  easily be tested in the real world
• Interpreting measurements
• (e.g., filling in spatial and temporal gaps
  between measurements)
• Providing Source-Receptor Information (maybe the
  only way to really get this)

13
The Role and Potential Value of Models
3. Models are a test of our collective knowledge

• They attempt to synthesize everything important
  that we know about a given system
• If a model fails, it means that we may not know
  everything we need to know

14
The Role and Potential Value of Models
4. Whether we like it or not, models are used in
developing answers to essentially all information
necessary for policy decisions

• EFFECTS (e.g., on human and wildlife health)
• CAUSES (e.g., environmental fate and transport of
  emitted substances)
• COSTS (e.g. for remediation)

15
Atmospheric Mercury Modeling Project
Overall Project Goal
Develop atmospheric mercury source-receptor
information for the Great Lakes, the Gulf of
Maine, and other selected receptors, to
determine the relative contributions of different
source regions (local, regional, national,
continental, global) source categories (e.g.,
coal combustion, waste incineration, etc.)
to the atmospheric deposition to any given
receptor
16
Overall Methodology

• Start with atmospheric mercury emissions
  inventory
• Perform atmospheric fate and transport modeling
  of these emissions (using a modified version of
  NOAAs HSYPLIT model)
• Keep track of source-receptor information during
  the modeling
• Evaluate the modeling by comparison of the
  predictions against ambient monitoring data
• If model is performing satisfactorily, report
  source-receptor results from the simulations
• (Similar to earlier work with dioxin and
  atrazine)
• Today, some preliminary results

17
(No Transcript)
18
(No Transcript)
19
(No Transcript)
20
1995 Global Hg Emissions Inventory, courtesy of
Josef Pacyna, NILU, Norway (2001)
21
(No Transcript)
22
(No Transcript)
23
Features of HYSPLIT-basedModeling System
1. Source-receptor information is crucial, but
difficult to obtain with most models because of
numerical limitations (tagged species selective
omission of emissions sources or regions)
Innovative interpolation techniques have been
developed (taking advantage of the trace nature
of pollutants such as Hg) that estimate the
impact of each source in an inventory on each
receptor being considered
24
Features of HYSPLIT-basedModeling System

• Source-receptor relationships are highly
  episodic, and so long periods of simulation are
  required to estimate representative averages
• However, most atmospheric fate and transport
  models can be run only for short episodes due to
  numerical limitations (they run in real time)

The HYSPLIT-based system is computationally
efficient enough to allow year-long simulations
to be performed. Even longer simulations could
be carried out.
25
Source-Receptor relationships are highly
variable thus need long-term simulations to
develop representative averages
26
Features of HYSPLIT-basedModeling System

• There are substantial uncertainties in the
  atmospheric fate and transport modeling of
  mercury, and so detailed sensitivity and
  bounding analyses should be conducted
• However, most atmospheric fate and transport
  models require such extensive computational
  resources, such uncertainty analyses are rarely
  carried out

The HYSPLIT-based system is computationally
efficient enough to allow extensive uncertainty
analyses to be conducted. Nobody knows what
the exact answers are in mercury modeling, but
the HYSPLIT system can tell you what the possible
range of answers is. This often turns out to be
most of what you need to know!
27
The emissions inventory was found to be the most
significant source of modeling uncertainty in
estimating dioxin deposition to Lake
Superior.(this kind of analysis is very
unusual)
As an example
28
Features of HYSPLIT-basedModeling System

• For policy considerations, it would be useful to
  be able to examine the potential effects of a
  number of different regulatory/emissions
  scenarios
• However, most atmospheric fate and transport
  models require new simulations for each scenario
  analyzed, and due to computational resource
  limitations, extensive scenario analyses are
  generally rather impractical to carry out

The interpolation features of the HYSPLIT-based
system allow emissions scenarios to be examined
without new model runs being conducted A
spreadsheet-based source-receptor matrix is
developed that allows anyone to see the results
of adjusting emissions from any or all sources in
the inventory
29
Transfer Coefficients for Hg are strongly
influenced by the type of Hg emitted Hg(II)
has much greaterlocal impacts than Hg(0)
30
(No Transcript)
31
Model-predicted deposition to Lake Michigan is
consistent with empirical, measurement-based
estimates from Lake Michigan Mass Balance Study
(for both deposition amount and flux)
32
(No Transcript)
33
(No Transcript)
34
(No Transcript)
35
(No Transcript)
36
NOAA/ARL Work in Developing Source-Receptor Relationships for Atmospheric Mercury Pollution in North America NOAA/ARL Work in Developing Source-Receptor Relationships for Atmospheric Mercury Pollution in North America NOAA/ARL Work in Developing Source-Receptor Relationships for Atmospheric Mercury Pollution in North America
Work to Date Future Work
Model Development Initial Hg-HYSPLIT model Refined Hg-HYSPLIT model (e.g, updated and more sophisticated chemistry treatment)
Model Evaluation Comparison of model predictions against Lake Michigan Mass Balance Study estimates (encouraging!) More detailed evaluation by comparison against MDN and other data
Sources Considered 95 Canadian Emissions 96/99 U.S. Emissions 00 Canadian Emissions 99 U.S. Emissions 99 Mexican Emissions 95 Global Emissions
Receptors Considered Great Lakes Gulf of Maine Great Lakes Gulf of Maine Additional selected receptors in the U.S., Canada, and Mexico
Funding Sources CEC EPA NOAA CEC? EPA? NOAA? GLPF?
37
(No Transcript)
38
(No Transcript)
39
(No Transcript)
40
(No Transcript)
41
NOAA Science Auditorium, Silver Spring, MD, Feb
14, 2002,in speech announcing his Clear Skies
Initiative
That mercury, its bad stuff!