Indoor emissions of total and fluorescent supermicron particles during HOMEChem

Inhalation of particulate matter is associated with adverse health outcomes. The fluorescent portion of supermicron particulate matter has been used as a proxy for bioaerosols. The sources and emission rates of fluorescent particles in residential environments are not well-understood. Using an ultraviolet aerodynamic particle sizer (UVAPS), emissions of total and fluorescent supermicron particles from common human activities were investigated during the HOMEChem campaign, a test-house investigation of the chemistry of indoor environments. Human occupancy and activities, including cooking and mopping, were found to be considerable sources of indoor supermicron fluorescent particles, which enhanced the indoor particle concentrations by two orders of magnitude above baseline levels. The estimated total (fluorescent) mass emission rates for the activities tested were in the range of 4-30 (1-11) mg per person meal for cooking and 0.1-4.9 (0.05-4.7) mg/h for occupancy and mopping. Model calculations indicate that, once released, the dominant fate of coarse particles (2.5-10 micrometer in diameter) was deposition onto indoor surfaces, allowing for the possibility of subsequent resuspension and consequent exposures over durations much longer than the ventilation time scale. Indoor coarse particle deposition would also contribute to soiling of indoor surfaces.     

Transport of particulate and gaseous pollutants in the vicinity of a human body

A uniform pollutant concentration in indoor environments can be an inappropriate representation of breathing concentration. This is especially true when local airflow in the vicinity of an occupant is dominant in transporting pollutants. The present study investigates the airflow in the vicinity of a human body, effects of respiration on breathing concentration of particulate and gaseous pollutants, and inhalation exposure in relation to source position and overall airflow patterns. It is based on experiments with a human simulator in a full-scale environmental chamber. Airflow and pollutant concentrations in the vicinity of a thermal manikin are monitored, while varying parameters including breathing, arm/hand movements, and ventilation system. Results show that breathing of a sedentary manikin has a measurable influence on the airflow in breathing zone, whereas it has very small impacts on occupant thermal plume. Also, localized hand motions have insignificant effects on the thermal plume. The results indicate that overall airflow pattern affect the inhaled particle concentrations. With highly mixed airflow in the space, relatively uniform concentration patterns occur in the occupant vicinity. However, with stratified airflow patterns, non-uniform concentration patterns are observed due to the occupant thermal plume. With a particle source at floor level and in near proximity to an occupant, inhaled particle concentrations are up to four times higher than the ambient concentrations. This finding implies that occupant thermal plume may play a significant role in transporting pollutants from floor level to the breathing zone. The non-uniform concentration observed with stratified flow also suggests caution in estimating inhalation exposure using a “well-mixed” mass balance model.     

Elliptic cylinder geometry for distinguishability analysis in impedance tomography

Electrical impedance tomography (EIT) is a technique that computes the cross-sectional impedance distribution within the body by using current and voltage measurements made on the body surface. It has been reported that the image reconstruction is distorted considerably when the boundary shape is considered to be more elliptical than circular as a more realistic shape for the measurement boundary. This paper describes an alternative framework for determining the distinguishability region with a finite measurement precision for different conductivity distributions in a body modeled by elliptic cylinder geometry. The distinguishable regions are compared in terms of modeling error for predefined inhomogeneities with elliptical and circular approaches for a noncircular measurement boundary at the body surface. Since most objects investigated by EIT are noncircular in shape, the analytical solution for the forward problem for the elliptical cross section approach is shown to be useful in order to reach a better assessment of the distinguishability region defined in a noncircular boundary. This paper is concentrated on centered elliptic inhomogeneity in the elliptical boundary and an analytic solution for this type of forward problem. The distinguishability performance of elliptical cross section with cosine injected current patterns is examined for different parameters of elliptical geometry.     

Effect of indoor buoyancy flow on wind-driven cross ventilation

Designing for wind-driven cross ventilation is challenging due to many factors. While studies have focused on the difficulty of predicting the total flow rate and measuring opening characteristics of cross ventilation, few have investigated the impacts on the distribution of indoor air. This paper provides insights on how local heat sources can generate significant buoyancy driven flow and affect indoor mixing during wind-driven cross ventilation scenarios. Measurements of air distribution were conducted by a tracer gas method for a multi-zone test building located in Austin, Texas, USA, along with cross ventilation flow at the openings. A computational fluid dynamic (CFD) model was also developed for this test building, which utilizes the measured flow properties at the openings as boundary conditions. Resulting air distribution patterns from the CFD model were then compared to the experimental data, validating the model. Further parametric analyses were also conducted to demonstrate the effect of interior heat loads in driving internal air mixing. Key findings of the investigation suggest a local heat source smaller than 35 W/m² can increase the indoor mixing during cross ventilation from less than 1 air exchange to as high as 8 air exchanges per hour. This result also suggests a typical occupancy scenario (people and electronics) can generate enough heat loads to change the indoor air mixing and alter the effect of cross ventilation.     

Operational characteristics of residential and light-commercial air-conditioning systems in a hot and humid climate zone

Forced-air space-conditioning systems are ubiquitous in U.S. residential and light-commercial buildings, yet gaps exist in our knowledge of how they operate in real environments. This investigation strengthens the knowledge base of smaller air-conditioning systems by characterizing a variety of operational characteristics measured in 17 existing residential and light-commercial air-conditioning systems operating in the cooling mode in Austin, Texas. Some key findings include: measured airflow rates were outside of the range recommended by most manufacturers for almost every system; actual measured cooling capacities were less than two-thirds of rated cooling capacities on average; hourly fractional operation times increased approximately 6% for every °C increase in indoor–outdoor temperature difference; and lower mean indoor surrogate thermostat settings and higher supply duct leakage fractions were most associated with longer operation times. The operational characteristics and parameters detailed herein provide insight into the magnitude of the effects of HVAC systems on both energy consumption and indoor air quality (IAQ) in residential and light-commercial buildings.     

Impact of placement of portable air cleaning devices in multizone residential environments

An advantage of portable air cleaners is that they can be positioned in different parts of a building and used where air cleaning is needed. This makes them a popular choice for use in residential buildings. In typical indoor particle modeling efforts, perfect air mixing and uniform contaminant concentration distribution are assumed. However, nonuniform spatial concentrations of particles are more reflective of most environments. Using experiments to validate computational fluid dynamic and particle tracking models and applying these models in numerical based parametric analysis, this paper analyzes the overall contaminant removal in a multi-room residential building. Simulations varied (1) particle size (0.74, 3.4 and 10 μm), (2) clean air delivery rate (CADR) of the air cleaner (50 m³/h and 500 m³/h), and (3) position of portable air cleaner in different rooms. The results show very large variation of the overall particle removal for different positions of portable cleaning device. In extreme cases, the effective positioning of cleaning device can result in a factor of 2.5 change in overall particle removal and, consequently, strongly affect occupant exposure to particles.     

A readout IC for an uncooled microbolometer infrared FPA with on-chip self-heating compensation in 0.35 μm CMOS

This paper describes a readout integrated circuit architecture for an infrared focal plane array intended for infrared network-attached video cameras in surveillance applications. The focal plane array consists of 352 × 288 uncooled thin-film microbolometer detectors with a pitch of 25 μm, enabling ambient temperature operation. The circuit features a low-noise readout path, detector resistance mismatch correction and a non-linear ramped current pulse scheme for the electrical biasing of the detectors in order to relax the dynamic range requirement of amplifiers and the ADC in the readout channel, imposed by detector process variation and self-heating during readout. The design is implemented in a 0.35-μm standard CMOS process and two versions of a smaller 32 × 32-pixel test chip have been fabricated and measured for evaluation. The latest test chip achieves a dynamic range of 97 dB and an input-referred RMS noise voltage of 6.4 μV yielding an estimated NETD value of 26 mK with f/1 optics. At a frame rate of 60 FPS the chip dissipates 170 mW of power from a 3.4 V supply.     

A 2.1 μW 80 dB SNR DT ΔΣ modulator for medical implant devices in 65 nm CMOS

This paper presents a simple and robust low-power ΔΣ modulator for accurate ADCs in implantable cardiac rhythm management devices such as pacemakers. Taking advantage of the very low signal bandwidth of 500 Hz which enables high oversampling ratio, the objective is to obtain high SNDR and low power consumption, while limiting the complexity of the modulator to a second-order architecture. Significant power reduction is achieved by utilizing a two-stage load-compensated OTA as well as the low-V_T devices in analog circuits and switches, allowing the modulator to operate at 0.9 V supply. Fabricated in a 65 nm CMOS technology, the modulator achieves 80 dB peak SNR and 76 dB peak SNDR over a 500 Hz signal bandwidth. With a power consumption of 2.1 μW, the modulator obtains 0.4 pJ/step FOM. To the authors’ knowledge, this is the lowest reported FOM, compared to the previously reported second-order modulators for such low-speed applications. The achieved FOM is also comparable to the best reported results from the higher-order ΔΣ modulators.     

Wind Tunnel Study on Aerodynamic Particle Resuspension from Monolayer and Multilayer Deposits on Linoleum Flooring and Galvanized Sheet Metal

Resuspension is an important source of indoor particles and the amount of dust loading is an important factor in resuspension emission rates. Field studies have shown that light to heavy dust loads can be found in the indoor environment, on both the surfaces of flooring and ventilation ducts. These diverse particle deposits can be broadly classified as either a monolayer, in which particles are sparsely deposited on a surface, or a multilayer, in which particles are deposited on top of one another and there is particle-to-particle adhesion and interaction. This experimental wind tunnel study explores the role of the type of particle deposit on aerodynamic resuspension from linoleum flooring and galvanized sheet metal. Resuspension fractions are reported for both monolayer and multilayer deposits exposed to a wide range of air velocities. The type of particle deposit is found to strongly influence resuspension. In general, the results show that resuspension from multilayer deposits can occur at significantly lower velocities compared with monolayer deposits. For example, resuspension fractions at an air velocity of 5 m/s for the canopy layer of multilayer deposits were similar to those found for monolayer deposits at 50 m/s. Additionally, for multilayer deposits, resuspension fractions for the canopy layer increased with increasing dust load and negligible resuspension occurred along the surface layer. It was found that the relationship between the particle deposit height and the viscous sublayer thickness of the airflow can help explain the differences in resuspension that were observed between the two types of deposits. The impact of the type of particle deposit on resuspension may have important implications for resuspension in the indoor environment, where a diversity of deposits can be found.

Copyright 2013 American Association for Aerosol Research