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rss_1.0 Recursos de colección

Caltech Authors (89,577 recursos)
Repository of works by Caltech published authors.

Group = Environmental Quality Laboratory

Mostrando recursos 1 - 20 de 107

1. Updated chemical mechanism for atmospheric photooxidation of toluene - Leone, Joseph A.; Seinfeld, John H.
A new reaction mechanism describing the atmospheric photochemical oxidation of toluene is formulated and tested against environmental chamber data from the University of California, Riverside, Statewide Air Pollution Research Center (SAPRC). On simulations of toluene—NO_x and toluene—benzaldehyde—NO_x irradiations, the average predicted O_3 and PAN maxima are within 3% of the experimental values. Simulations performed with the new mechanism are used to investigate various mechanistic paths, and to gain insight into areas where our understanding is not complete. Specific areas that are investigated include benzaldehyde photolysis, organic nitrate formation, alternate ring fragmentation pathways, and conjugated γ-dicarbonyl condensation to the aerosol phase.

2. Verification of image processing based visibility models - Larson, Susan M.; Cass, Glen R.; Hussey, Kevin J.; Luce, Frederick
Methods are presented for testing visibility models that use simulated photographs to display results of model calculations. An experimental protocol is developed and used to obtain input data including standard photographs of chosen scenes on a clear day and during a smog event at Pasadena, CA. With the clear day photograph as a substrate, pollutant properties measured on the smoggy day are introduced into the visibility model, and results of the model calculations are displayed as a synthetic photograph of the expected appearance of the smog event. Quantitative comparisons are made between the predicted and actual appearance of the smog event. Diagnostic techniques developed are applied to the visibility modeling procedure proposed by...

3. Thermodynamic Equilibrium Properties of Aqueous Solutions of Nitrate, Sulfate and Ammonium - Stelson, Arthur W.; Bassett, Mark E.; Seinfeld, John H.
Knowledge of the thermodynamic equilibrium properties of aqueous solutions is required in virtually any calculation associated with particle and droplet acidification. For example, prediction of the equilibrium vapor pressures of dissolved solutes and water is necessary when predicting the rate of uptake of pollutant gases into cloud- and raindrops and aerosol particles. In addition, evidence indicates that atmospheric aerosols and small droplets are frequently in chemical equilibrium with the local surrounding air. In such a situation, given the ambient gaseous concentrations of pollutant species, and the temperature and relative humidity, it is desired to determine the physical state (liquid or solid) and the chemical composition of the particle or...

4. Consumer Surplus Under Uncertainty: An Application to Dam-Reservoir Projects - Quirk, James
The use of cost-benefit analysis to evaluate the net welfare payoffs from water projects has now been an established practice for many years. One of the interesting aspects of such cost-benefit studies is that water projects involve an uncertain flow of costs and benefits, arising from the stochastic nature of streamflows. Hence a basic problem for the cost-benefit analyst is that of incorporating this uncertainty into his measures of costs and benefits. In the present paper we examine the problem of computing an appropriate consumer surplus measure to evaluate water project benefits under uncertainty. Detailed treatment is given to the...

5. Shoreline Impact from Ocean Waste Discharges - Koh, Robert C. Y.
A methodology is presented which enables estimation of the advective transport probabilities from a coastal wastewater discharge based on information that can be obtained from current measurements. From these, shoreline impact can be assessed, and the tendency for background buildup and benthic accumulation estimated. The method utilizes measured data to obtain parameter values to allow synthetic currents to be generated that can in turn be used in a Monte Carlo scheme for obtaining the advective transport probabilities. The method permits enhancement and improvement of the estimates when the amount and extent of data coverage are expanded.

6. Ozone fading of natural organic colorants: mechanisms and products of the reaction of ozone with indigos - Grosjean, Daniel; Whltmore, Paul M.; Cass, Glen R.
Indigo, dibromoindigo, and colorants containing thioindigo and tetrachlorothioindigo were exposed in the dark to dry, purified air containing ozone (10 ppm) for 4 days, and the exposed samples were analyzed by mass spectrometry. Under the conditions employed, indigo and dibromoindigo were entirely consumed, and the major reaction products were isatin and isatoic anhydride from indigo and bromoisatin and bromoisatoic anhydride from dibromoindigo. Thioindigo and its chloro derivative also reacted with ozone, though at a slower rate; the corresponding substituted isatins and anhydrides were tentatively identified as reaction products. These results can be rationalized in terms of a mechanism involving electrophilic addition of ozone onto the unsaturated carboncarbon bond. This mechanism adequately describes the observed loss...

7. Surface charge and adsorption properties of chrysotile asbestos in natural waters - Bales, Roger C.; Morgan, James J.
Changes in surface-charge adsorption properties of chrysotile asbestos aging in water were studied in a series of constant-pH laboratory experiments. Chrysotile freshly suspended in an inorganic electrolyte has a positive surface charge below pH 8.9. Charge reversal occurs within about 2 weeks due to more rapid dissolution of chrysotile's outer magnesium hydroxide surface relative to the underlying silica component of the mineral. The inorganic anions NO_3^-, Cl^-, HCO_3^- , and SO_4^(2-) did not absorb. A constant- capacitance model can be used to relate surface charge to adsorption of protons over the pH range 7-9. At natural organic matter (NOM) concentrations at or below those encountered in natural waters, the particles can adsorb sufficient...

8. Estimation of Atmospheric Species Concentrations from Remote Sensing Data - Omatu, Sigeru; Seinfeld, John H.
A basic problem in the interpretation of atmospheric remote sensing data is to estimate species concentration distributions. Typical remote sensing data involve a field of view that moves across the region and represent integrated species burdens from the ground to the altitude of the instrument. The estimation problem arising from this special measurement configuration is solved based on the partial differential equation for atmospheric diffusion and Wiener-Hopf theory. The estimation of the concentration distribution downwind of a hypothetical continous ground-level source of pollutants is studied numerically.

9. Environmental data display - Hussey, Kevin J.; Blackwell, Richard J.; McRae, Gregory J.; Seinfeld, John H.
Large amounts of information can be portrayed in very compact form and used for many applications, thanks to a combination of color-coded graphics and image processing techniques.

10. Statistical distributions of air pollutant concentrations - Georgopoulos, Panos G.; Seinfeld, John H.
Air pollutant concentrations are inherently random variables because of their dependence on the fluctuations of a variety of meteorological and emission variables. When sets of air quality data are available, various statistical characteristics can be determined and assigned to the pollutant concentrations.

11. Design and use of a collector for the in situ isolation of particulate trace organic species in precipitation - Mazurek, M. A.; Simoneit, B. R. T.; Standley, L. J.; Friedman, D.; Beeman, C.
Extracts of particulate organic matter were examined for discrete rainfall events from metropolitan Los Angeles, California, using an in situ filtration technique. Filtration efficiency was 98 % for the collection of extractable organic C associated with particles having nominal diameters greater than 0m22 μm Organic background levels of less than 260 ng per sample were determined. Rainwater particle samples were extracted with repeated hexane and benzene: isopropanol (2: 1) solvent additions using ultrasonic agitation. Extract mixtures were quantified by high-resolution gas chromatography (HRGC) and were adjusted for component losses with perdeuterated recovery standards. Yields for the neutral fractions ranged from...

12. Basinwide nitric acid and related species concentrations observed during the Claremont nitrogen species comparison study - Solomon, Paul A.; Larson, Susan M.; Fall, Theresa; Cass, Glen R.
In conjunction with the Claremont Nitrogen Species Comparison Study, tandem filter units designed to collect HNO_3/total aerosol (TA) NO_3− and NH_3/TA NH+_4 were operated at seven locations throughout the Los Angeles area, including Claremont. The sampling methods used were related to the comparison study via intensive short-term and long-term measurements made at Claremont by both the tandem filter method and the denuder difference method. Between methods, 4-h and 6-h duration HNO_3 samples taken by the tandem filter method were higher (~ 20%) than the HNO_3 results obtained by the denuder difference method. As sampling duration increased to 22 h, the...

13. Sensivity Analysis of Chemically Reacting Systems - Tilden, J. W.; Costanza, V.; McRae, G. J.; Seinfeld, J. H.
The complexity of systems of chemical reactions makes it difficult to determine the effect uncertainties in rate constants and other parameters have on the behavior of .the species concentrations. Mathematically, the sensitivity analysis of a system of chemical reactions consists in the problem of determining the effect of uncertainties in parameters and initial conditions on the solution of a set of ordinary differential equations. Sensitivity analysis procedures may be classed as deterministic or stochastic in nature. Currently available sensitivity analysis techniques are reviewed, and the entire problem is presented in a unified framework.

14. Sulfate air quality control strategy design - Cass, Glen R.
An approach to the design of emission control strategies for sulfate air quality improvement is described. Methods developed are tested within a case study of the nature and causes of the high sulfate levels observed in the Los Angeles area. An air quality model for sulfate formation and transport is developed which computes long-term average sulfate concentrations using a Lagrangian marked particle technique. The air quality model is verified by application to the Los Angeles air basin during each month of the years 1972 to 1974. The time sequence of observed sulfate air quality is reproduced closely in spite of the...

15. Numerical solution of the atmospheric diffusion equation for chemically reacting flows - McRae, Gregory J.; Goodin, William R.; Seinfeld, John H.
A comprehensive study of numerical techniques for solving the atmospheric diffusion equation is reported. Operator splitting methods are examined in which the three-dimensional problem is converted into a sequence of one-dimensional problems. A Galerkin, linear finite element scheme with a nonlinear filter is found to be computationally superior to the other methods tested for the advection-diffusion components. The chemical reaction dynamics component, treated within the splitting scheme, is generally highly stiff. A second-order predictor, iterated corrector technique, in combination with an asymptotic treatment of the stiff components, is found to be computationally superior for the chemical kinetics. The validity of...

16. Sensitivity analysis of a mathematical model for photochemical air pollution - Tilden, James W.; Seinfeld, John H.
The effect of simultaneous ± 50 per cent uncertainties in the emission and meteorological parameters on the predictions of a mathematical model for photochemical air pollution is studied. Predicted concentrations are found to be most sensitive to uncertainties in mixing height, photolysis intensity, initial conditions and emission intensity. A general method for air quality model sensitivity analysis is discussed and employed.

17. Mathematical modeling of the formation and transport of ammonium nitrate aerosol - Russell, Armistead G.; McRae, Gregory J.; Cass, Glen R.
A mathematical model describing the transport and formation of aerosol NH_4NO_3 is presented. Based on a vertically resolved Lagrangian trajectory formulation incorporating gas phase kinetics, NH_4NO_3 concentrations are computed at thermodynamic equilibrium with precursor HNO_3 vapor and NH_3 concentrations. Sensitivity analysis shows that NH_4NO_3 concentration predictions are strongly influenced by ambient temperature and NH_3 levels. A brief description of the NH_3 emissions inventory used in this study is included to indicate the important sources. The model was tested by comparison to ambient NH_3, NH_4+ and NO_3− concentrations measured at El Monte, California during June 1974. Model results compare favorably with...

18. Sensitivity Analysis of Distributed Parameter Systems - Koda, Masato; Seinfeld, John H.
A method is developed for the calculation of sensitivity coefficients of general distributed parameter systems to the variation of spatially and temporally varying parameters appearing in the system equations and initial and boundary conditions.

19. Sensitivity and Uncertainty of Reaction Mechanisms for Photochemical Air Pollution - Falls, Andrew H.; McRae, Gregory J.; Seinfeld, John H.
A sensitivity/uncertainty analysis is performed on a mechanism describing the chemistry of the polluted troposphere. General features of the photochemical reaction system are outlined together with an assessment of the uncertainties associated with the formulations of mechanistic details and rate data. The combined effects of sensitivity and uncertainty are determined using the Fourier amplitude sensitivity test (FAST) method. The results of this analysis identify the key parameters influencing the chemistry of NO_2, O_3, and PAN. Based on these findings, a series of recommendations are made for future experimental kinetic studies.

20. Automatic Sensitivity Analysis of Kinetic Mechanisms - Koda, Masato; McRae, Gregory J.; Seinfeld, J. H.
An algorithm for the automatic sensitivity analysis of kinetic mechanisms based on the Fourier amplitude sensitivity test (FAST) method of Shuler and co-workers is reported. The algorithm computes a measure of the relative sensitivity of each concentration to each parameter of interest, such as rate constants, Arrhenius parameters, stoichiometric coefficients, and initial concentrations. Arbitrary variations in the magnitude of the parameters are allowable. The algorithm is illustrated for the simple example of computing the sensitivity of the concentration of species A to variation of the two Arrhenius parameters for the hypothetical reaction A + A →.

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