our effort prone to both overgeneralization and oversimplification. To reduce such difficulties, we will often refer to examples of regulatory model development, especially those from air quality modeling. Box 1-1 in Chapter 1 contains a brief history of EPA’s effort to model tropospheric ozone.


Some regulatory models arise from those developed as general research tools. Others were developed specifically for addressing regulatory issues. They have been developed by EPA scientists, academia, national laboratories, or the private sector. Some of the most complex models have benefited from contributions by almost all of the above. For example, complex regional chemical transport models for simulating air quality usually include components contributed by multiple parties. The urban airshed model (UAM), heavily used for the design of ozone control strategies in the 1980s and 1990s, was developed by a private company (Systems Applications International) relying on contributions of academia and on support from public and private organizations. The major air quality model developed for use in-house by EPA is the community multiscale air quality (CMAQ) model (EPA 1999b). EPA and NOAA scientists developed the most recent CMAQ model in partnership with a nonprofit organization (Microelectronics Center of North Carolina) and contributions by academia funded by EPA, the National Science Foundation and state authorities, most prominently California authorities (CMAS 2006). A variation of CMAQ, called CMAQ-MADRID, has been developed by a private company (Atmospheric and Environmental Research, Inc) using the CMAQ model as a starting point and adding components developed by academic researchers or by company scientists (Zhang et al. 2004). A private organization, Electric Power Research Institute, provided funding for the CMAQ-MADRID development. All the above codes are in the public domain.

Under the Toxic Substances Control Act, EPA must make individual pre-manufacturing decisions on 2,000 new chemicals per year before a new chemical can enter the market. Because of the large number of decisions, the agency has had to rely on screening tools that predict properties from chemical structure. EPA uses EPI (Estimation Programs Interface) Suite, which consists of several quantitative structure-activity relationships (QSARs) models that are available in the public domain.

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