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We’re Experts in Air Exposure Assessment
Air exposure assessment, risk assessment, and risk management are key parts of evaluating risks from air pollutants. At Sullivan Environmental, we lead in creating methods for air exposure assessment and have worked with the U.S. EPA and industry clients to identify exposures from various sources.
Risk Assessment and Risk Management
Risk assessment in terms of air exposure assessment evaluates average and worst-case exposures concerning cancer risks and non-cancer safety limits. By identifying significant risks from pollutants and their sources, we can emphasize which ones require more attention. Risk management focuses on finding the most effective and affordable methods to reduce these risks (average and maximum exposures). Sullivan Environmental Consulting specializes in these areas, primarily concentrating on air exposure assessments.
Acute Exposures
A few averaging periods per year, each with emission rates greatly exceeding routine conditions, can dominate air exposure assessments when averaging times are 24 hours or less. Examples of this include:
- – Batch operations at chemical facilities
- – Pesticide applications in agricultural fields
- – Dump stack emissions from hazardous waste incinerators
In all cases, there is a major limitation in terms of applying routine Gaussian dispersion models. This limitation is how to define meteorological conditions when the emissions event of concern takes place. There are two major options, as follows:
The most simplistic way, which is only appropriate as a default, is to assume that the worst-case emission event occurs every hour of the year. If we screen the exposure assessment on this basis, there is no need for further refinement of the analysis. On the other hand, if the imposition of such conservative assumptions would result in additional controls or permit restrictions, the next appropriate step is to account for the variability in emission rates by using a Monte Carlo treatment.
The TOXST model for the chemical industry was developed by Sullivan Environmental, and later adopted by the EPA. This model provides a preferred option to refine the estimation of acute exposures. It provides the ability to simulate 200 to 2,000 years of operation to produce distributions of concentrations for receptors around the source.
TOXST can account for batch emissions, mutually exclusive sources, and multiple averaging times up to 24 hours. Although TOXST is not directly supported by the current EPA dispersion model, AERMOD, the principles used in TOXST can be applied by Sullivan Environmental in terms of pre-processing and post-processing to meet current air quality modeling requirements consistent with the algorithms in the TOXST model.
Chronic Exposures
The goals of assessment are similar whether the exposure study is a threshold or non-threshold evaluation. Specifically, locations in close proximity to key sources are modeled with as much specificity as possible regarding the release characteristics of nearby sources. Similarly, simplifying assumptions concerning the spatial aggregation of sources.
Similarly, this applies to the treatment of building downwash. This also applies to other site-specific features are usually of much greater significance as the distance between the source and receptor decreases.
Additionally, the diurnal characteristics of the sources can be important in some cases. During the daytime, diurnal features model operations. This is primarily due to the strong bias towards restrictive dispersion conditions that create worst-case scenarios for near-ground sources during many nighttime periods. Particularly for non-cancer endpoints with threshold effects, it is essential to incorporate background concentrations into the modeled concentrations for sources within the modeling domain.
Finally, if measured air quality data are available, model performance testing provides an opportunity to identify strengths and weaknesses. These include the emissions and modeling treatments as well as the potential to enhance model performance. When sufficient measured air quality or soil concentration data are available, it is recommended that testing be conducted on this basis. This is to evaluate performance for modeled deposition. The above features are integrated into the EPA Air Quality Integrated Management System (AIMS) developed by Sullivan Environmental.
In the mid 1990’s, the system was installed in the Baltimore metropolitan area. This was a prototype for managing air quality at the urban scale. It is utilized as one of the three urban air toxic studies conducted by the EPA as mandated by the Clean Air Act of 1990. This study is referred to as the Baltimore Air Toxics Study. A system such as AIMS offers the potential to provide effective air quality management in the future.
Emergency Release
One of the most serious concerns regarding toxic air pollutant exposures is the consequence of an emergency release. For example, a chlorine discharge from the rupture of a major storage tank can produce lethal effects at distances far from the point of release. Miles from the point of release, adverse health effects can be observed. Sullivan Environmental has developed a modeling system for air quality emergencies. This software is RISKMANpro ™, which computes source terms (the temperature of the release, gas or liquid fractions, and emission rates. This supports dispersion modeling of dense gas and non-dense gas releases.
Furthermore, this system can also be used to estimate the benefits of mitigation measures such as dikes and sheltering of storage tanks within an enclosure. Another feature of RISKMANpro ™ is the option to estimate a range of expected indoor concentrations as a function of time after release, which can be used to assess shelter-in-place versus evacuation options.
Advantages
- At Sullivan Environmental, we are at the forefront of developing methods for air exposure assessment .
- We have conducted research for the U.S. EPA and industrial clients aimed at identifying exposures from specific source categories.
- The senior scientists responsible for managing modeling projects are both certified consulting meteorologists, each with over 40 years of experience.
Benefits
- Air exposure assessment is a primary area of expertise for Sullivan Environmental.
- The senior scientists employed by the firm are experts in air quality and have managed complex modeling projects and legal cases involving air quality and meteorological expert analysis.
- Sullivan Environmental developed systems such as the EPA Air Quality Integrated Management System (AIMS) as a prototype system for managing air quality at the urban-scale of analysis and a modeling system for air quality emergencies, called RISKMANpro ™, which computes sources terms to support dispersion modeling of dense gas and non-dense gas releases.