Ashok J. Gadgil

Modeling Emissions of Volatile Organic Compounds from New Carpets

A simple model is proposed to account for observed emissions of volatile organic compounds (VOCs) from new carpets. The model assumes that the VOCs originate predominantly in a uniform slab of polymer backing material. Parameters for the model (the initial concentration of a VOC in the polymer, a diffusion coefficient and an equilibrium polymer/air partition coefficient) are obtained from experimental data produced by a previous chamber study. The diffusion coefficients generally decrease as the molecular weight of the VOCs increase, while the polymer/air partition coefficients generally increase as the vapor pressure of the compounds decrease. In addition, for two of the study carpets that have a styrene-butadiene rubber (SBR) backing, the diffusion and partition coefficients are similar to independently reported values for SBR. The results suggest that predictions of VOCs emissions from new carpets may be possible based solely on a knowledge of the physical properties of the relevant compounds and the carpet backing material. However, a more rigorous validation of the model is desirable.

Rapidly Locating and Characterizing Pollutant Releases in Buildings

Abstract Releases of airborne contaminants in or near a building can lead to significant human exposures unless prompt response measures are taken. However, possible responses can include conflicting strategies, such as shutting the ventilation system off versus running it in a purge mode or having occupants evacuate versus sheltering in place. The proper choice depends in part on knowing the source locations, the amounts released, and the likely future dispersion routes of the pollutants. We present an approach that estimates this information in real time. It applies Bayesian statistics to interpret measurements of airborne pollutant concentrations from multiple sensors placed in the building and computes best estimates and uncertainties of the release conditions. The algorithm is fast, capable of continuously updating the estimates as measurements stream in from sensors. We demonstrate the approach using a hypothetical pollutant release in a five-room building. Unknowns to the interpretation algorithm include location, duration, and strength of the source, and some building and weather conditions. Two sensor sampling plans and three levels of data quality are examined. Data interpretation in all examples is rapid; however, locating and characterizing the source with high probability depends on the amount and quality of data and the sampling plan.

Removing arsenic from synthetic groundwater with iron electrocoagulation: an Fe and As K-edge EXAFS study.

Electrocoagulation (EC) using iron electrodes is a promising arsenic removal strategy for Bangladesh groundwater drinking supplies. EC is based on the rapid in situ dissolution of a sacrificial Fe(0) anode to generate iron precipitates with a high arsenic sorption affinity. We used X-ray absorption spectroscopy (XAS) to investigate the local coordination environment (<4.0 Å) of Fe and As in EC precipitates generated in synthetic Bangladesh groundwater (SBGW). Fe and As K-edge EXAFS spectra were found to be similar between samples regardless of the large range of current density (0.02, 1.1, 5.0, 100 mA/cm(2)) used to generate samples. Shell-by-shell fits of the Fe K-edge EXAFS spectra indicated that EC precipitates consist of primarily edge-sharing FeO(6) octahedra. The absence of corner-sharing FeO(6) octahedra implies that EC precipitates resemble nanoscale clusters (polymers) of edge-sharing octahedra that efficiently bind arsenic. Shell-by-shell fits of As K-edge EXAFS spectra show that arsenic, initially present as a mixture of As(III) and As(V), forms primarily binuclear, corner-sharing As(V) surface complexes on EC precipitates. This specific coordination geometry prevents the formation of FeO(6) corner-sharing linkages. Phosphate and silicate, abundant in SBGW, likely influence the structure of EC precipitates in a similar way by preventing FeO(6) corner-sharing linkages. This study provides a better understanding of the structure, reactivity, and colloidal stability of EC precipitates and the behavior of arsenic during EC. The results also offer useful constraints for predicting arsenic remobilization during the long-term disposal of EC sludge.

Modeling As(III) oxidation and removal with iron electrocoagulation in groundwater.

Understanding the chemical kinetics of arsenic during electrocoagulation (EC) treatment is essential for a deeper understanding of arsenic removal using EC under a variety of operating conditions and solution compositions. We describe a highly constrained, simple chemical dynamic model of As(III) oxidation and As(III,V), Si, and P sorption for the EC system using model parameters extracted from some of our experimental results and previous studies. Our model predictions agree well with both data extracted from previous studies and our observed experimental data over a broad range of operating conditions (charge dosage rate) and solution chemistry (pH, co-occurring ions) without free model parameters. Our model provides insights into why higher pH and lower charge dosage rate (Coulombs/L/min) facilitate As(III) removal by EC and sheds light on the debate in the recent published literature regarding the mechanism of As(III) oxidation during EC. Our model also provides practically useful estimates of the minimum amount of iron required to remove 500 μg/L As(III) to <50 μg/L. Parameters measured in this work include the ratio of rate constants for Fe(II) and As(III) reactions with Fe(IV) in synthetic groundwater (k(1)/k(2) = 1.07) and the apparent rate constant of Fe(II) oxidation with dissolved oxygen at pH 7 (k(app) = 10(0.22) M(-1)s(-1)).

Novel approach for tomographic reconstruction of gas concentration distributions in air: Use of smooth basis functions and simulated annealing

Optical remote sensing and iterative computed tomography (CT) can be applied to measure the spatial distribution of gaseous pollutant concentrations. We conducted chamber experiments to test this combination of techniques using an open path Fourier transform infrared spectrometer (OP-FTIR) and a standard algebraic reconstruction technique (ART). Although ART converged to solutions that showed excellent agreement with the measured ray-integral concentrations, the solutions were inconsistent with simultaneously gathered point-sample concentration measurements. A new CT method was developed that combines (1) the superposition of bivariate Gaussians to represent the concentration distribution and (2) a simulated annealing minimization routine to find the parameters of the Gaussian basis functions that result in the best fit to the ray-integral concentration data. This method, named smooth basis function minimization (SBFM), generated reconstructions that agreed well, both qualitatively and quantitatively, with the concentration profiles generated from point sampling. We present an analysis of two sets of experimental data that compares the performance of ART and SBFM. We conclude that SBFM is a superior CT reconstruction method for practical indoor and outdoor air monitoring applications.

Imaging Indoor Tracer-Gas Concentrations with Computed Tomography: Experimental Results with a Remote Sensing FTIR System

This work demonstrates for the first time the feasibility of computed tomography (CT) reconstructions of pollutant concentrations in a real room setting. A remote sensing Fourier transform infrared spectrometer was mounted on a moving base in a controlled ventilation chamber. A passive tracer was released from a point source into the room under constant ventilation conditions. A series of experiments gathered multiple path-averaged measurements in a two-dimensional plane for CT reconstruction. Simultaneous readings were gathered with a multiple-point sampling array for later comparison to the CT reconstructed concentrations. Good qualitative agreement between the reconstruction and point sample data was obtained. Limitations encountered due to the temporal resolution, size, and geometry of the experimental apparatus are clearly surmountable with better instrumentation.

Stationary and time-dependent indoor tracer-gas concentration profiles measured by OP-FTIR remote sensing and SBFM-computed tomography

Measurement of gas concentrations in indoor air using optical remote sensing (ORS) and computed tomography (CT) has been suggested but not thoroughly investigated. We present experiments in which one time-varying and 11 different steady-state tracer-gas concentration profiles were generated in a ventilated chamber and sampled in a horizontal plane by an open-path Fourier transform infrared (OP-FTIR) spectrometer for subsequent CT inversion. CT reconstructions were performed using the recently developed smooth basis function minimization (SBFM) technique. The CT reconstructions were compared with simultaneously gathered point-sample concentration measurements. Agreement between the two sampling methods was qualitatively very good, with concentration profiles generated by both methods showing the same features of peak location and shape. Quantitative agreement was generally good to within 50%. We discuss the sources of discrepancy and suggest directions for future research, especially with regard to monitoring time-dependent processes. With further refinements in the SBFM algorithm and improvements in optical remote sensing hardware, this technique promises to yield rapid and accurate measurements of the spatial distribution of gases in indoor environments.

Conservation screening curves to compare efficiency investments to power plants

CONSERVATION SCREENING CURVES TO COMPARE EFFICIENCY INVESTMENTS TO POWER PLANTS: APPLICATIONS TO COMMERCIAL SECTOR CONSERVATION PROGRAMS Jonathan Koomey, Arthur H. Rosenfeld, and Ashok Gadgil Center for Building Science Lawrence Berkeley Laboratory, Bdg 90-4000 Berkeley, CA 94720 (510) 486-5974, (510) 486-4247 Fax Published in the Proceedings of the 1990 ACEEE Summer Study on Energy Efficiency in Buildings Asilomar, CA, August 1990 The work described in this paper was funded by the Assistant Secretary for Conservation and Renewable Energy, Office of Buildings and Community Systems, Building Systems Division of the U.S. Department of Energy, under Contract No. DE-AC03-76SF00098.

Conservation potential of compact fluorescent lamps in India and Brazil

LBL-27210 UC-350 ITl1 Lawrence Berkeley Laboratory Ii;;I UNIVERSITY OF CALIFORNIA I APPLI ED SCI ENCE DIVISION Conservation Potential of Compact Fluorescent Lamps in India and Brazil A. Gadgi1 and G. De Martino Jannuzzi July 1989 I APPLIED SCIENCE DIVISION Prepared for the U.S. Department of Energy under Contract Number DE-AC03-76SF00098.

Predicting regional lung deposition of environmental tobacco smoke particles

Inhalation exposure to environmental tobacco smoke (ETS) particles may increase health risks, but only to the extent that the particles deposit in the respiratory tract. We describe a technique to predict regional lung deposition of environmental tobacco smoke particles. Interpretation of particle size distribution measurements after cigarette combustion by a smoking machine in a test room yields an effective emissions profile. An aerosol dynamics model is used to predict indoor particle concentrations resulting from a specified combination of smoking frequency and building factors. By utilizing a lung deposition model, the rate of ETS mass accumulation in human lungs is then determined as a function of particle size and lung airway generation. Considering emissions of sidestream smoke only, residential exposures of nonsmokers to ETS are predicted to cause rates of total respiratory tract particle deposition in the range of 0.4–0.7 μg / day per kg of body weight for light smoking in a well-ventilated resi...