Inventory Representation For Chemical

UVCB substances are substances of unknown or variable composition, complex reaction products, and biological materials that cannot be represented by unique structures and molecular formulas. Some UVCB substances are not adequately described by their CA Names and have supplemental definitions that are considered integral parts of the names for TSCA purposes. The guidance, entitled Toxic Substances Control Act Inventory Representation For Chemical Substances Of Unknown Or Variable Composition, Complex Reaction Products And Biological Materials UVCB Substances points out that any substance that matches a CA Name but is not covered by the substance description is not considered to be covered by that Inventory listing. 

Toxic Substances Control Act Inventory Representation For Chemical Substances Of Unknown Or Variable Composition, Complex Reaction Products And Biological Materials UVCB Substances UVCB Substances... 

Toxic Substances Control Act Inventory Representation For Chemical... 

The Environmental Protection Agency (EPA) explained the conventions applied to listings of polymeric chemical substances for purposes of Premanufacture Notification (PMN) reporting and the TSCA Inventory. The principal guidance document in which the conventions are explained is titled Toxic Substances Control Act Inventory Representation for Polymeric Substances, which was published on 29 March 1995. This discussion of polymer nomenclature conventions under TSCA begins with general guidelines, followed by a discussion of how polymers are identified... 

The EPA explained its preferred methods for representing polymers on the Inventory in its 1995 Toxic Substances Control Act Inventory Representation for Polymeric Substances, and began by defining what substances can be hsted on the Inventory as polymers.For this purpose, EPA defined polymers as sequences of one or more types of monomer units, where a monomer unit is the reacted form of a monomer bonded to two or more other molecules. A polymer must also have a distribution of molecules of different molecular weights attributable primarily to different numbers of monomer units in the molecules. If all the molecules of a specific substance always have the same chain length then that substance is described on the Inventory as a specific substance with a defined structure and molecular weight, and not as a polymer. There are limited exceptions to this rule. Some chemicals that chemists may consider to be polymers do not fall within this definition because they do not have a distribution of molecular weights. 

The guidance on how to name complex reaction products is entitled Toxic Substances Control Act Inventory Representation for Combinations of Two or More Substances Complex Reaction Products. It applies only to chemicals made by a chemical reaction, and not to formulated mixtures, which are made simply by mixing with no chemical reaction. Its primary purpose is to explain when complex reaction products should be named as one reaction product, or as a series of individual components. 

Letter from Mary E. Cushmac, Chief, Policy and Administrative Section, New Chemicals Branch, to Fred H. Parry of Hoechst Celanese Corporation (Aug. 12,1994) in collection of h 7 Letters Toxic Substances Control Act Inventory Representation For Polymeric Substances Polymeric Substances... 

T Trban airshed models are mathematical representations of atmospheric transport, dispersion, and chemical reaction processes which when combined with a source emissions model and inventory and pertinent meteorological data may be used to predict pollutant concentrations at any point in the airshed. Models capable of accurate prediction will be important aids in urban and regional planning. These models will be used for ... 

Fundamental to the TSCA Inventory is the principle that entries on the Inventory are identified as precisely as possible for the commercial chemical substance, as reported by the submitter. Substances that are chemically indistinguishable, or even identical, may be listed differently on the Inventory, depending on the degree of knowledge that the submitters possess and report about such substances, as well as how submitters intend to represent the chemical identities to the EPA and to customers. Although these chemically indistinguishable substances are named differently on the Inventory, this is not a nomenclature issue, but an issue of substance representation as required by the EPA. Submitters should be aware that their choice for substance representation has an important role in the EPA s determination of how the substance will be listed on the Inventory. 

This basic picture of organic aerosol was relatively well developed by the end of the 1990s. Chemical transport models were fed by inventories for POA emissions from a wide array of sources, and those emissions were treated in a variety of microphysics modules as effectively non-volatile and often chemically inert particles [19, 20]. SOA models evolved from relatively primitive treatments that simply converted a fixed fraction of VOC emissions into equally non-volatile secondary material (for example 12% of monoterpene emissions) to more sophisticated two-product representations that treated the equilibrium partitioning of surrogate species based on smog-chamber experiments [21-23]. Even today some global-scale models represent SOA as a fixed non-volatile fraction of VOC emissions [24, 25]. 

As noted above, there are cases where we need more accurate representations of how chemical concentration varies with depth. For example, we may be interested in transfers of chemicals from air to shallow ground water or want to consider how long-term applications of pesticides to the soil surface can impact terrestrial ecosystems—including burrowing creatures. However, we also wish to maintain a simple mathematical mass-balance structure of the multimedia model. To illustrate how we can set up a multilayer model that accurately captures soil mass transport processes, we next derive a vertical compartment structure with an air and three soil compartments, but any number of environmental compartments and soil layers can be employed in this scheme. Figure 8.6 provides a schematic of three soil layers linked to an air compartment and carrying pollutants downward to a saturated zone. We represent the inventory in each vertical compartment i, as M, (mol), transformation rate constants as kt, and transfer factors as ky (d ). The latter account for the rate of transfer between each i and j compartment pair. 

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