Tracer hybrid models

Tracer Hybrid Receptor Model (Lewis). Lewis and Stevens (3) have derived a hybrid receptor model for describing the secondary sulfate from an SO2 point source. The resulting expression for secondary sulfate concentration M o at the receptor has the form... 

Tracer Hybrid Receptor Model Application. Even though the Deep Creek Lake data base is not yet complete, in terms of all the chemical analyses that are anticipated to be included, it may be useful to give a simple illustration of how a hybrid receptor model can provide some insight into the data. 

Under the assumption that the gaseous sulfur, fine particle selenium and secondary fine particle sulfur measured at an ambient site originates from a single point source the tracer hybrid receptor model can be expressed in terms of the two equations... 

Lewis and Stevens (This Volume and 12) have provided a useful framework for hybrid receptor modeling in which one calculates concentrations of various sulfur species relative to those of some tracer that is fairly unique to the sulfur source, e.g., Se as a tracer from coal-fired power plants. Equations are written for S02 conversion... 

The meaning of the the term "hybrid receptor model" is not consistent in the literature. Following the definition proposed at the Quail Roost Receptor Modeling Workshop (15), we take it to be a combination of some meteorological aspects of traditional source-based models with some tracer aspects of receptor models. An important feature of such models is that one often works with ratios of species so that some of the most uncertain absolute parameters of classical models cancel out. As noted below, for example, one can calculate the concentration ratio of gas-phase SO2 to gas-phase B as a function of distance from a common source more accurately than the absolute concentration of either species. 

In this study we have employed the simultaneous collection of atmospheric particles and gases followed by multielement analysis as an approach for the determination of source-receptor relationships. A number of particulate tracer elements have previously been linked to sources (e.g., V to identify oil-fired power plant emissions, Na for marine aerosols, and Pb for motor vehicle contribution). Receptor methods commonly used to assess the interregional impact of such emissions include chemical mass balances (CMBs) and factor analysis (FA), the latter often including wind trajectories. With CMBs, source-strengths are determined (1) from the relative concentrations of marker elements measured at emission sources. When enough sample analyses are available, correlation calculations from FA and knowledge of source-emission compositions may identify groups of species from a common source type and identify potential marker elements. The source composition patterns are not necessary as the elemental concentrations in each sample are normalized to the mean value of the element. Recently a hybrid receptor model was proposed by Lewis and Stevens (2) in which the dispersion, deposition, and conversion characteristics of sulfur species in power-plant emissions... 

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