Charles D. Litton

An Inexpensive Dual-Chamber Particle Monitor: Laboratory Characterization

Abstract In developing countries, high levels of particle pollution from the use of coal and biomass fuels for household cooking and heating are a major cause of ill health and premature mortality. The cost and complexity of existing monitoring equipment, combined with the need to sample many locations, make routine quantification of household particle pollution levels difficult. Recent advances in technology, however, have enabled the development of a small, portable, data-logging particle monitor modified from commercial smoke alarm technology that can meet the needs of surveys in the developing world at reasonable cost. Laboratory comparisons of a prototype particle monitor developed at the University of California at Berkeley (UCB) with gravi-metric filters, a tapered element oscillating microbalance, and a TSI DustTrak to quantify the UCB particle monitor response as a function of both concentration and particle size and to examine sensor response in relation to changes in temperature, relative humidity, and elevation are presented here. UCB particle monitors showed good linearity in response to different concentrations of laboratory-generated oleic acid aerosols with a coarse (mass median diameter, 2.1 µm) and fine (mass median diameter, 0.27–0.42 µm) size distributions (average r2 = 0.997 ± 0.005). The photoelectric and ionization chamber showed a wide range of responses based on particle size and, thus, require calibration with the aerosol of interest. The ionization chamber was five times more sensitive to fine rather than coarse particles, whereas the photoelectric chamber was five times more sensitive to coarse than fine. The ratio of the response between the two sensors has the potential for mass calibration of individual data points based on estimated parameters of the size distribution. The results demonstrate the significant potential of this monitor, which will facilitate the evaluation of interventions (improved fuels, stoves, and ventilation) on indoor air pollution levels and research on the impacts of indoor particle levels on health in developing countries.

Combined Optical and Ionization Measurement Techniques for Inexpensive Characterization of Micrometer and Submicrometer Aerosols

This article describes a simple combination ionization chamber and angular scattering sensor and presents the results of laboratory experiments to define its response to micrometer and submicrometer aerosols as a function of aerosol mass, surface, and diameter. The results of these experiments indicate that a simple theory is adequate to describe the operation of the sensor and presents correlations and techniques that will allow the sensor to be used for measurement and characterization of aerosols over a broad spectrum of possible applications related to adverse environmental and health consequences. For particles with volume mean diameters in the range of ~ 150–500 nm, the measured sensor responses yielded signal-to-noise ratios in the range of ~25 to > 500 for mass concentrations in the range of 0.50 to 16 mg/m3.

Studies of the measurement of respirable coal dusts and diesel particulate matter

Experiments were conducted to determine the optical scattering properties of respirable coal dusts and diesel particulate matter (DPM) at discrete angles in the forward direction and at light source wavelengths of 632.8 and 635 nm. In addition to the scattering data, simultaneous measurements were made of the total mass concentration of dust, DPM or mixtures of the two, and the responses of a unipolar ion chamber and a simpler, more common bipolar ion chamber typical of residential smoke detectors. The results of these experiments indicate, for respirable coal dusts, that the intensity per unit mass concentration at discrete angles in the range of 15°-30° varies linearly with mass concentration independent of the volatility of the dust, but that at larger scattering angles, intensities per unit mass concentration are affected by dust volatility. For DPM, the intensities per unit mass concentration are significantly lower. The results also indicate that the ion chambers respond significantly to DPM while there is no response to respirable coal dust, and that when mixtures of the two are present, the ion chambers respond to the DPM mass fraction only. In addition, it was found that the angular intensity distribution for respirable dusts is adequately described by classical Mie scattering theory, while for DPM classical Mie scattering is inadequate, and treatment of the particles as fractal-like aggregates yields much better agreement with the experimental data. This paper describes the experiments and their results.

A Detailed Study of the Properties of Smoke Particles Produced from both Flaming and Non-Flaming Combustion of Common Mine Combustibles

This paper presents the results obtained from detailed studies of the properties of smoke particles produced from a wide range of flaming and non-flaming combustible materials and discusses how these properties impact early-warning fire detection as well as the hazards of smoke particle toxicity and reduced visibility that can significantly affect life safety. Data acquired include discrete angular scattering at wavelengths of 635 nm and 532 nm; visible light obscuration; light extinction at a wavelength of 532 nm and total light scattering at a wavelength of 520 nm; the responses of calibrated combination ionization/photoelectric smoke sensor; and total mass concentrations. These data are subsequently used to define the size, morphology and radiative transfer properties of the fractal aggregate smoke particles including radius of gyration, primary particle diameter, number of primary particles per aggregate, mass of an aggregate, mass extinction, scattering and absorption coefficients and the resultant albedo. Scanning electron microscope (SEM)/transmission electron microscope (TEM) data and computer-generated fractal aggregates are compared to determine similar morphologies and then used to calculate theoretical values of scattering, absorption, and extinction efficiencies using both the discrete dipole approximation (DDA) and the Rayleigh-Debye-Gans (RDG) approximation for subsequent comparison to the experimental data. These data and analyses indicate that significant differences exist between flaming and non-flaming smoke particles in terms of size, morphology and radiative transfer properties. From a practical viewpoint, the analyses also indicate possible techniques for development of improved early warning fire sensors and smarter, discriminating fire sensors that can function in hostile, contaminated atmospheres such as mines and tunnels. These atmospheres may contain significant levels of combustion products from internal combustion engines, such as diesels, that are used routinely in underground mines. In addition, the much higher albedos measured for non-flaming smoke particles are indicative of significantly lower carbon content and higher levels of volatile organic compounds that have the potential for increased acute toxicity due to their higher reactivity. The paper demonstrates how the basic data can be used to implement improved fire detection systems and improve our ability to assess hazards resulting from potentially catastrophic mine fires.

Small, Smart, Fast, and Cheap: Microchip-Based Sensors to Estimate Air Pollution Exposures in Rural Households

Over the last 20 years, the Kirk R. Smith research group at the University of California Berkeley—in collaboration with Electronically Monitored Ecosystems, Berkeley Air Monitoring Group, and other academic institutions—has developed a suite of relatively inexpensive, rugged, battery-operated, microchip-based devices to quantify parameters related to household air pollution. These devices include two generations of particle monitors; data-logging temperature sensors to assess time of use of household energy devices; a time-activity monitoring system using ultrasound; and a CO2-based tracer-decay system to assess ventilation rates. Development of each system involved numerous iterations of custom hardware, software, and data processing and visualization routines along with both lab and field validation. The devices have been used in hundreds of studies globally and have greatly enhanced our understanding of heterogeneous household air pollution (HAP) concentrations and exposures and factors influencing them.