|
Items in cart [0] |
Questions? Call 888-624-8373 |
| Copyright © 2009. National Academy of Sciences. All rights reserved. Terms of Use and Privacy Statement |
Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 1
Executive Summary
The National Academies workshop "Tracking and Predicting the Dispersion of
Hazardous Agents" brought together atmospheric scientists from academia,
government laboratories, and the private sector; emergency management officials
and first responders; and experts in national security, risk communication, and other
relevant fields. Workshop participants examined how meteorological observations and
dispersion models can be used by emergency managers in the context of an atmospheric
release of hazardous chemical, biological, or nuclear (C/B/N) agents. It was found that
atmospheric observational and modeling tools can contribute substantively to preparation
and planning for possible future events, to emergency response in the minutes to hours
after an event occurs, and to the post-event recovery and analysis. Existing capabilities
generally are useful, but emergency responders have a number of observational and
modeling needs that are not well satisfied by existing services. Although it may never be
possible to provide a "perfect" atmospheric dispersion prediction for any individual
hazardous release, the committee believes that with more effective application of avai-
lable tools and development of new technologies and capabilities, the atmospheric
science community could play a larger role in addressing this critical national security
concern.
The organizing committee extracted a number of important lessons from the work-
shop discussions and, in its subsequent deliberations, identified the following as key
findings and recommendations.
MEETING THE NEEDS OF EMERGENCY RESPONDERS
Atmospheric observations and dispersion models must interface seamIessly with
the needs of emergency responders. Emergency response managers would benefit from
training that conveys the strengths and weaknesses of existing observational and
dispersion modeling tools and the situations under which various types of tools perform
best. Conversely, dispersion modelers and meteorologists would benefit from learning
how nowcasts and forecasts are used in emergency response situations. "Tabletop" (i.e.,
roundtable discussion and planning) event simulation exercises should be convened
OCR for page 2
2
ATMOSPHERIC DISPERSION OF HAZARDOUS MATERIAL RELEASES
regularly to bring together emergency response teams and members of the atmo-
spheric modeling and observational communities to help establish and exercise a
common set of data interface and decision support protocols.
Emergency responders face a confusing array of seemingly competitive atmo-
spheric transport model systems supported by various agencies, and in many cases, they
do not have a clear understanding of where to turn for immediate assistance. A single
federal point of contact should be established (such as a 1-X00 phone number) that
could be used to connect emergency responders across the country to appropriate
dispersion modeling centers for immediate assistance.
Emergency managers need a realistic understanding of the bounds on the un-
certainties of dispersion model predictions. Dispersion model predictions of the con-
centrations for a given release need to be accompanied by a prediction of the event-to-
event variability in that situation. Dispersion modelers should use ensemble modeling
or other approaches that quantify not only the average downwind concentration
distribution in a given situation (which is interpretable as the most likely outcome)
but also the event-to-event variability to be expected. The specific formats of the
information presented should be developed in close collaboration with users of this
information.
ENHANCING OBSERVATIONAL RESOURCES
The most basic observations required for tracking and predicting the dispersion of a
hazardous agent include identification of the plume, characterization of low-level winds
(to follow the plume trajectory), characterization of the depth and intensity of the
turbulent layers through which the plume moves (to estimate plume spread), and identi-
f~cation of areas of potential agent degradation and dry or wet deposition.
The current array of surface observational systems needs to be better used and
enhanced. Many surface stations are poorly exposed and have limited instrument quality
control, and instrument locations are not necessarily optimal for model initialization or
identification of local flows. Furthermore, it often is difficult to obtain the data from
multiple observational arrays, especially in real time. A comprehensive survey of the
capabilities and limitations of existing observational networks should be conducted,
followed by action to improve these networks and access to them, especially around
more vulnerable areas.
Doppler radar systems can be useful for estimating boundary layer winds,
monitoring precipitation, and possibly tracking some C/B/N plumes. NRC (2002b)
recommended evaluating the potential for supplementing the current Doppler radar
network with subnetworks of short-range, short-wavelength radars. This would enable
better estimates and coverage of low-level winds, increase the likelihood of detecting
C/B/N plumes, and improve precipitation (and hence wet deposition) estimates. The
~ ,
committee supports this recommendation and further recommends that the design
and data collection strategy of this radar network be optimized to include providing
information for supporting response to a C/11/N release.
OCR for page 3
EXECUTIVE SUMMARY
3
Radar wind profilers and radio acoustic sounding system profilers, which measure
variations of the horizontal wind and temperature, respectively, with height and enable
identification of turbulent layers, provide important information for response to C/B/N
attacks and are relatively inexpensive and easy to maintain. Wind and temperature
profilers should become an integral part of regional and local fixed-observational
networks.
Mobile observational platforms can provide valuable information and fulfill multi-
ple needs in the first minutes to hours after a hazardous release. Unmanned aerial
vehicles (UAVs) can be used to measure wind and temperature profiles and to char-
acterize turbulence where other platforms cannot easily reach. Mobile lidars and radars
can, in some contexts, be used for plume tracking and wind field characterization.
However, civilian instruments currently are available only for research use. There
should be continued development of portable scanning lidars and radars on air-
borne and surface-mobile platforms for research, and plans should be developed to
make such instruments rapidly available for effective, timely use in vulnerable
areas.
Local topography and the built environment lead to local wind patterns that can
carry contaminants in unexpected directions. Observational networks must represent
these local flows as faithfully as possible. Improvements in these networks can be
achieved through routine data monitoring and comparison of observed flows with local-
to regional-scale model simulations and through numerical modeling, including observ-
ing system simulation experiments. Studies should be performed over a range of weather
situations and for both daytime and nighttime conditions. Such exercises will educate
meteorologists about local flows and model capabilities; the resulting knowledge of what
to believe when observational data and models convey different messages is vital in
response to an emergency situation. Efforts should be made to systematically
characterize local-scale windflow patterns (over the full diurnal cycle) in areas
deemed to be potential terrorist targets with the goals of optimizing fixed
observations and educating those involved in developing dispersion forecasts about
local flows and model strengths and weaknesses.
Focused field exercises are needed to understand the behavior of modeled transport
and dispersion in different weather regimes and C/B/N release scenarios, particularly for
nocturnal conditions. It is not practical to verify dispersion and transport models for
every area with comprehensive field programs, but for an appropriate range of
meteorological conditions, physical modeling in a wind tunnel could assist in dispersion
model evaluation and threat assessment. In addition, field programs conducted for other
purposes, such as improvement of weather forecasting or understanding boundary layer
turbulence also can be useful. There should be continued field programs focused on
7 — — — — —— —— — — —— ~— — _ e'— — — —__ _ — _ _ __ _ _ __
1~ ~ ~ · ~ ~ ~ ~ ~ ~ ~ ~ · ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
(~/K/N release issues, and datasets from field programs with a (~/K/N or related locus
should be made available for testing and development of dispersion and mesoscale
transport models.
Some of the actions recommended above (i.e., enhancing fixed observing arrays,
optimizing placement of surface stations and wind profilers, developing and deploying
portable scanning lidars, UAVs, and radars) will be costly. There should be priori-
OCR for page 4
4
ATMOSPHERIC DISPERSION OF HAZARDOUS MATERIAL RELEASES
tization of such actions based on identifying areas with the greatest need (e.g.,
highest population concentration, most complex flow, greatest likelihood for a
terrorist attack, most vulnerable facilities). Every effort should be made to utilize
such instrumentation for other (hazardous and non-hazardous) applications (e.g., to
enhance air pollution monitoring, optimize agricultural practices, aid in severe-
storm forecasting and highway network safety), thus sharing the costs and ensuring
that the array will be continuously used, maintained, evaluated, and quality con-
trolled.
STRENGTHENING MODELING CAPABILITIES AND
APPLICABILITY TO EMERGENCY RESPONSE
For purposes of threat assessment, preparation, and training, existing dispersion
models meet some needs of the emergency response community. In the case of actual
emergencies, the needs of emergency management may not be well satisfied by existing
models. In particular, single-event uncertainties in atmospheric dispersion models are not
well bounded, and current models are not well designed for complex natural topographies
or built urban environments.
Most available atmospheric dispersion models predict only the ensemble-average
concentration (that is, the average over a large number of realizations of a given dis-
nersion situation). New approaches are needed for modeling a single hazardous release.
Dispersion models used for emergency planning and response should provide
confidence estimates that prescribed concentrations will not be exceeded outside of
predicted hazard zones. This requires that models provide some measure of the possible
variability in a given situation.
Different dispersion modeling methodologies are required in the preparedness,
response, and recovery stages of C/B/N events. For the preparedness stage, an accurate
model capable of providing confidence-level estimates is desired, but model execution
time is not important. For the response stage, accuracy can be compromised to obtain
timely predictions, but the dispersion model must still provide confidence-level estimates.
For the recovery stage, model execution time is not important, but accurate model
reconstruction of the plume concentration distribution over time is desired. In order to
use a dispersion model's predictions effectively during the early response phase, the wind
field and other conditions at the site of the release must be available in near real time and
a short model execution time is essential. The most appropriate dispersion model for any
given scenario may depend on the quantity, toxicity, and persistence of the hazardous
agent; thus, it is critical that source identification be as rapid as possible.
The committee's review of selected existing dispersion modeling systems deter-
mined that no one system had all the features that the committee deemed critical:
confidence estimates for the predicted dosages, accommodation of urban and complex
topography, short execution time urban models for the response phase, and accurate
though slower models for the preparedness and recovery phases. Better integration
between existing and future modeling systems could supply all of these critical features.
OCR for page 5
EXECUTIVE SUMMARY
The "unpairing" of concentration predictions and observations in time and space
(commonly done with continuous sources in air quality applications) is inappropriate
when evaluating dispersion model performance in episodic releases. Evaluation tech-
niques based on more advanced probabilistic methods need to be developed. Toward that
end, existing dispersion models should identify the type of averaging (ensemble, time and
space) inherent in their modeling methodology, both in the wind field formulation and in
the treatment of dispersion. The reliability of existing and future dispersion modeling
systems should be evaluated against field and laboratory measurements for potential
C/B/N event scenarios. If predicted confidence limits are found to be unacceptable, then
empirical corrections should be applied to model outputs so as not to place emergency
personnel in harm's way. Increasing the density of the wind measurements in a plume's
domain will potentially reduce uncertainty, thus reducing the predicted extent of the
hazard without compromising confidence.
Meteorological observations are a critical element of dispersion modeling. Obser-
vational technologies have been evolving rapidly in recent decades, and the committee
identified many existing measurement technologies that have not been fully exploited
through data assimilation. Model operators and developers would benefit from broader
interaction with the meteorological community to take advantage of leading-edge
research in data assimilation, quantitative precipitation forecasting, short-range numerical
weather prediction, and high-resolution forecasting initialized with radar data. Likewise,
observational research programs studying issues such as weather prediction, properties of
boundary layer turbulence, and air pollution transport should be viewed as targets of
opportunity for testing and evaluating dispersion models.
Priorities for improving modeling capabilities include the following:
· New dispersion modeling constructs need to be further explored and possi-
bly adapted for operational use in urban settings. This includes advanced, short
execution time models, slower but more accurate computational fluid dynamics and
large-eddy simulation models, and models with adaptive grids.
Techniques must be developed for constructing ensembles of model
solutions on the urban scale so that probabilistic rather than deterministic
information can be provided to emergency managers. It will be necessary to
quantify the level of confidence as a function of the number of ensemble members,
which in turn, will have implications for the computational power required.
It is necessary to learn how to more effectively assimilate into models an
appropriate range of meteorological data (e.g., wind, temperature, and moisture
data) from observing systems as well as real-time data from C/B/N sensors,
especially as the quality and availability of these data increase. It also is important
to effectively couple dispersion models with appropriate source characterization
models.
Urban field programs and wind-tunnel urban simulations should be
conducted to allow for the testing, evaluation, and development of existing and new
modeling systems (both meteorological and dispersion models). Developing an
appropriate experimental design for such studies is a critical task that itself will
require careful evaluation.
OCR for page 6
6
ATMOSPHERIC DISPERSION OF HAZARDOUS MATERIAL RELEASES
The bulk effects of urban surfaces on the surface energy, moisture, and
momentum are not well accounted for in most meteorological models. Existing
development work in this area should be enhanced and the improved modeling
techniques adopted more widely.
· Urban building and topography three-dimensional databases need to be
developed and maintained for use in numerical and wind-tunnel dispersion simu-
lations.
MANAGEMENT AND COORDINATION NEEDS
There is a wide array of federal agencies that operate dispersion modeling systems,
including the Department of Commerce-National Oceanic and Atmospheric Admini-
stration, Department of Defense, Department of Energy, Environmental Protection
Agency, Federal Emergency Management Agency, and Nuclear Regulatory Commission,
along with numerous academic and private sector research groups that contribute to these
federal efforts. In addition, it must be recognized that the new Department of Homeland
Security, established in January 2003, may eventually augment or subsume some of the
activities and responsibilities currently residing in these other federal agencies. At the
present time, however, it is not known to the committee what specific organizational
plans are being considered.
Given the ambiguity of this situation and the limited time and resources available
to examine these management-related issues, the committee felt that it was not
appropriate to make specific suggestions about agency leadership responsibilities for the
various activities recommended in this report. The committee emphasizes, however, that
a carefully crafted management strategy, with clear lines of responsibility and authority,
is essential for ensuring further progress in the development and ongoing operation of
dispersion modeling systems. There is a clear need for more central coordination among
the various federal agencies currently involved and among the relevant players at the
local, regional, and national levels.
Each of the agencies mentioned above has developed its own "customer base" and
areas of strength and specialization; thus, it seems likely that some form of distributed
responsibility will continue to be the most effective organizational strategy. However, a
strong center of coordination is needed to ensure that the necessary research and
development work is carried out and that emergency responders have unambiguous
guidance as to where to turn for help.
A nationally coordinated effort should be established to foster support and
systematic evaluation of existing models and research and development of new
modeling approaches, undertaken in collaboration with the broader meteorological
community. The Office of the Federal Coordinator for Meteorology, which recently
organized a review of U.S. dispersion modeling capabilities, could provide valuable
input as to which agencyties) is best suited to oversee this coordinated effort.
In at least one large urban area, a fully operational dispersion tracking and
forecasting system should be established that is, a comprehensive system for
OCR for page 7
EXECUTIVE SUMMARY
7
collecting relevant meteorological and C/B/N sensor data, assimilating this
information into a dispersion model, and maintaining the expertise and organiza-
tional capacity to provide immediate model forecasts on a full-time basis. If
possible, a few such systems should be established and evaluated for different types
of urban areas (e.g., coastal versus continental cities, low-latitude versus high-
latitude cities). Such systems can be used as test beds for gaining understanding of
model capabilities and limitations, and their use should not be limited to emergency
situations. These observational and modeling tools could have multiple appli-
cations, which would help justify costs and ensure that the systems are frequently
used, maintained, evaluated, and quality controlled.
There is a wealth of knowledge about meteorological and dispersion models
residing in universities, National Weather Service Weather Forecast Offices, and
private sector facilities throughout the nation. These sources of expertise, together
with the existing programs in several national laboratories and military facilities,
should be integral components of the coordinated national effort recommended
above, to assist with developing local and regional models that are optimized for the
topography and seasonal weather patterns in vulnerable areas. At the most basic
level, this integration can be implemented via collaborative research and develop-
ment efforts.
Representative terms from entire chapter:
dispersion modeling
