The Atmospheric Sciences staff at Exponent provides consulting services in air quality and atmospheric sciences. Our staff specializes in air quality and meteorological modeling, permitting, and licensing. They investigate accidental releases of chemicals to the atmosphere, simulate transport and fate of chemical substances, and develop measures of prevention and control, such as emergency preparedness and response. Areas of air quality modeling include industrial plumes, dense gases, photochemical reactions, mobile sources, forest fires, explosions, radioactive releases, and odors. Clients benefit from our multidisciplinary approach, which includes the support of staff across multiple practice areas. Our atmospheric scientists work closely with chemical engineers, combustion specialists, atmospheric modelers, and thermal and process engineers to predict and evaluate the dispersion of air emissions. They also work with Exponent’s risk assessors to evaluate health risks posed by atmospheric releases to the ambient air and to indoor environments, as well as the health effects of air pollution.
We offer core services to our clients that include:
- Air quality modeling
- Meteorological modeling
- Model development
- Air quality permitting and licensing
- Litigation support
- Training courses
Who We Are
Exponent’s Atmospheric Sciences staff has experience serving a wide range of industrial and government clients around the world. They routinely apply models to predict the dispersion of pollutants emitted by industrial sources or to help manage the risk of potential chemical releases. Exponent’s worldwide industrial clients have included major companies operating aluminum facilities, oil refineries, chemical plants, electric generating stations, pulp and paper manufacturing, natural gas storage, and distribution and asphalt plants. Our atmospheric consultants have also worked with many government agencies, including the USDA Forest Service, the Department of the Interior, the U.S. EPA, and the United Nations International Atomic Energy Agency (IAEA).
The staff has also been influential in the evolution of air quality modeling. Exponent scientists have developed or contributed to five of the seven U.S. EPA models recommended in the Guideline on Air Quality Models. Most notable of these is the CALPUFF model, an advanced non-steady-state meteorological and air quality modeling system recommended by the EPA as the preferred model for assessing long-range transport of pollutants and their impacts on Federal Class I areas or for near-field applications involving complex meteorological conditions. Other EPA-recommended models that bear the imprint of the Atmospheric Sciences staff include the Buoyant Line and Point (BLP) source model commonly used for aluminum reduction facilities, the Offshore and Coastal Dispersion (OCD) model for emission sources in offshore or shoreline locations, and the Complex Terrain Dispersion Model (CTDM). Our staff also developed the PRIME building downwash model that is incorporated into the CALPUFF and AERMOD models.
As the developers of and contributors to many of the EPA-recommended models in the past 35 years, our scientists are experts on the models’ capabilities and limitations. This knowledge enables Exponent to provide solutions beyond the typical or traditional modeling approaches.
Capabilities
Air Quality Modeling
As the developers of the CALPUFF model, Exponent’s Atmospheric scientists offer expertise in applying CALPUFF to long-range transport modeling for Class I studies, Best Available Retrofit Technology (BART) analyses, modeling for near-field complex flows such as found in steep valleys or coastal environments, deposition of particulates or gases, and real-time air quality forecast systems.
Steady-state plume modeling is conducted routinely by Exponent with the EPA AERMOD modeling system.
We also offer deep experience in dense-gas dispersion modeling. Applications have included emergency planning, and accidental spills or upset conditions releasing ammonia, hydrogen sulfide, and chlorine from pipelines, rail cars, storage tanks, and flares. Models used include DEGADIS, HGSYSTEM, SLAB, ALOHA, PHAST, SCIPUFF, and FLUENT.
Photochemical grid models have been applied to help tackle regional ozone problems ranging from planning by state air agencies and evaluating mitigation measures to determine whether measured concentrations could be explained by source inventories. Some of the models that have been applied include CMAQ, developed by EPA scientists; CALGRID, developed by our Atmospheric Sciences staff, CAMx, and UAM-IV.
Air quality models have also been applied to odor evaluation and mitigation. In this case, the number of dilutions of the source’s emissions is compared to the known release concentrations and the odor threshold.
Other specialized modeling expertise includes mobile sources, forest fires, explosions, and radioactive releases.
Meteorological Modeling
In addition to air quality modeling, our consultants have applied prognostic numerical weather prediction models and diagnostic meteorological models for many years. These models are typically used to provide three-dimensional meteorological inputs for air quality models, especially in areas of sparse observational data, but have also been used to determine the feasibility of wind power generation, or providing wind forecasts for yacht races. The models applied include the Weather Research and Forecasting (WRF) model, the Mesoscale Meteorological (MM5) model, and The Air Pollution Model (TAPM) used in Australia. For example, meteorological modeling has been used by our atmospheric staff as the basis for automated, real-time, and forecast weather systems that have been implemented for industrial clients worldwide. Several forecasts of meteorological and air quality parameters are made each day and used by clients to operate in a manner that will minimize the risk of air pollutant problems.
Computational Fluid Dynamics Modeling
Computational Fluid Dynamics (CFD) is the modeling of fluid flow. CFD models solve the equations that govern the conservation of mass, momentum, and energy and include chemical reactions and multi-phase physics such as the droplets from flashing liquids. A mathematical prototype of the problem is constructed and divided into millions of grid cells. Using numerical methods, the CFD models converge to a solution of the equations. Our scientists have used both FLUENT and OpenFOAM software.
Exponent’s atmospheric consultants can apply CFD modeling to accidental releases of dense gases such as ammonia or chlorine, wind-induced pressure forces on buildings during hurricanes or severe storms; dispersion within oil refineries, industrial complexes, city centers or tunnels; flare plume rise; recirculation of cooling-tower air flow; re-entrainment of rooftop exhausts by building air intakes; pedestrian-level wind studies, or indoor issues such as laboratory hood design. Our atmospheric scientists work with our engineering staff to use these tools to supplement Exponent’s analytical, experimental, and field-based activities.
Air Quality Permitting and Licensing
Exponent’s scientists have an in-depth knowledge of air quality regulations, which along with our expertise in air quality modeling, makes us well qualified to help clients obtain permits for their sources. Our expertise includes problems involving Prevention of Significant Deterioration (PSD) analyses, compliance with National Ambient Air Quality (NAAQS) or New Source Review (NSR) requirements, risk management planning, evaluating visibility or deposition issues in National Parks, developing emissions inventories, and addressing nuisance issues such as odor. Our experience in model development is an advantage when selecting a modeling approach for demonstrating compliance with regulations and then defending that approach.
Litigation Support
Exponent’s atmospheric scientists provide expert testimony and litigation support to clients. The leading role of our scientists in the development of many of the EPA-recommended models helps us to simplify complex modeling concepts into understandable presentations.
Training Courses
Exponent’s atmospheric staff conduct regularly scheduled courses, open to the public, on the CALPUFF modeling system. Courses can also be arranged for private clients and government agencies. For example, courses have been taught to U.S. EPA personnel and state agencies, the U.S. Agency for International Development, the Air and Waste Management Association, the Clean Air Society of Australia and New Zealand, the National Association of Clean Air in South Africa, and universities in the United States, Chile, Italy, South Africa, Hong Kong, Australia, New Zealand, and Thailand.