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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

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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.

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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-

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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.

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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.

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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

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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.