Environ. Sci. Technol. 1990,24,1004-1013
Nitric Acid Concentrations in Southern California Museums Lynn G. Salmon, Wliliam W. Nazaroff,?Mary P. Ligocki, Michael C. Jones, and Glen R. Caw'
Environmental Engineering Science Department and Environmental Quality Laboratory, California Institute of Technology, Pasadena, California 9 1125 Measurements were made during two seasons at five Los Angeles area museums to determine the concentrations of nitric acid in outdoor and indoor air. Mean seasonal indoor nitric acid concentrations ranged from 0.5%, the organic carbon appears to be the predominant sorption phase. The only other important environmental variable appears to be the particle concentration itself (7). For the reversible (or labile) component of sorption, a model has been proposed (the particle interaction model) that predicts the partition coefficient of nonionic hydrophobic chemicals over a range of nearly 7 orders of magnitude with a log,, standard error of 0.38 (8). Review of Previous Models for Surfactant Sorption. The sorption of surfactants to clay and mineral + HydroQual
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* Manhattan College.
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particles has been extensively studied and a number of reviews are available (9-11). A description of surfactant sorption has been proposed that identifies three distinct regions of the isotherm (12,13). The sorption at low solution concentrations conforms to a linear isotherm. At higher concentrations a Langmuir isotherm fits the data. Generally, this corresponds to the concentration range of surfactants in the environment of micrograms per liter to low milligrams per liter. The experimental data base for sorption of surfactants to inorganic adsorbents is quite extensive. The effect of chain length (14-16),position of the hydrophilic group (13, pH, and ionic strength (13,18,19)have all been investigated. The effect of particle concentration has also been observed (20,21). The focus of the surfactant sorption models proposed to date has been on the form of the isotherm (21-27). The sorption of surfactants to sediments has been less extensively examined. Data have been fit with linear (28, 29),Langmuir (30),and Freundlich (31-33) isotherms. The use of fraction organic carbon and octanol-water partition coefficient has been suggested as correlating parameters (28,29).The purpose of this paper is to present a model for the sorption of anionic surfactants that is constructed in the same spirit as the models for nonionic hydrophobic organic chemicals, including the particle interaction effect.
Sorption Model Scope. The purpose of the data analysis presented below is to identify the correlating parameters for the partition coefficient. The scope of the investigation is limited in a number of ways. First, the investigation is restricted to soils, sediments, and sludges that are directly relevant to environmental fate and effects. Although the clay literature is large, it is unclear how to apply these results to natural sediments and soils. Second, only the linear portion of the isotherm is considered. It is possible that environmentally relevant concentrations could exceed the linear range. However, a model of the linear portion of the isotherm, which is characterized by the partition coefficient, is a necessary first step. Finally, the data are limited to anionic surfactants. Although some data for cationic (34-36) and nonionic (28)surfactants have been reported, the number of observations are too few to establish statistically valid model parameters for these classes of chemicals. The approach taken to the model building is as follows. First, data from diverse sources are evaluated for the presence of a minimum number of necessary parameters. The model is patterned after the model for nonionic hydrophobic organic chemicals (6, 8). The critical micelle concentration (CMC) of the surfactant is the analogue of KO, in the models for nonionic hydrophobic organic
0 1990 American Chemical Society
Environ. Sci. Technol., Vol. 24, No. 7, 1990
1013
