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EFFECTIVE ACIDITY CONSTANT BEHAVIOR NEAR ZERO CHARGE CONDITIONS
Loux, N T. EFFECTIVE ACIDITY CONSTANT BEHAVIOR NEAR ZERO CHARGE CONDITIONS. Presented at 222nd American Chemical Society National Meeting, Chicago, IL, August 26-30, 2001.
This research project sets out to design and conduct an assessment of the long-term ecological consequences of alternative management choices. As the first project to be done at this scale using predictive ecological endpoints, we will seek to identify the appropriate components of such an analysis. We will use experience gained in the conduct of this BASE analysis to identify key research and data needs for address, to estimate timing, resource needs, etc., for future analyses. We will extend this analysis beyond previous and ongoing studies in two ways: by incorporating biological endpoints, primarily properties of fish communities, and by introducing the concept of sustainability of ecological state under future scenarios contrasted with the present state of those same ecological resources. Requirements that are identified during the course of this study will permit the recommendation of specific capabilities that should be incorporated in a general modeling system currently under development to support BASE and other environmental assessments. Finally, the analysis is intended to be of value for establishing environmental management choices that will be beneficial and those that would be detrimental to the sustainability of ecological resources of the Albemarle-Pamlico Basin.
Surface site (>SOH group) acidity reactions require expressions of the form: Ka = [>SOHn-1(z-1)]aH+EXP(-DG/RT)/[>SOHnz] (where all variables have their usual meaning). One can rearrange this expression to generate an effective acidity constant historically defined as: Qa = KaEXP(DG/RT) = [>SOHn-1(z-1)]aH+/[>SOHnz]; effective acidity constant behavior can be used to probe interfacial energetics. Although deriving estimates of Qa for monoprotic systems is straightforward, deriving estimates of Qa1 and Qa2 from biprotic systems is much more ambiguous. Two alternatives to the traditional pHzpc extrapolation procedure will be introduced and tested with computer generated data of known accuracy. All three methods will be applied to experimental data published in the technical literature for the purpose of possibly explaining anomalous DG behavior in the pHzpc region within the context of charging energies (Loux, 2000) and aggregation-derived experimental artifact.
Record Details:Record Type: DOCUMENT (PRESENTATION/ABSTRACT)
Organization:U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
NATIONAL EXPOSURE RESEARCH LABORATORY
ECOSYSTEMS RESEARCH DIVISION
ECOSYSTEMS ASSESSMENT BRANCH