The following summaries are examples of past and ongoing research projects at UT. These projects have been made possible by a wide range of sponsors, from government to industry and not-for-profit organizations.
Energy Implications of Filters in Residential and Light Commercial Construction
Exposure to Toxic Air Contaminants
HVAC Filters as Passive Samplers
The Role of Surfaces in Secondary Organic Aerosol Formation
p-Dichlorobenzene in Homes: Sources and Risks
Near-Source Exposures to Toxic Air Contaminants in Cleaning Products
Passive Removal of Ozone from Buildings
The Chemistry and Biology of Green Building Materials
Effective Positioning of Portable Air Cleaning Devices in Multizone Residential Buildings
Analysis of Spatial and Temporal Pollutant Dispersion in Residential Buildings
Transport of Particulate and Gaseous Pollutants in the Vicinity of a Human Body
Development of Internal Surface Convection Correlations for Energy Calculations and Indoor Modeling
Indoor Air Quality Implications of Portable Ion Generators
Ozone-Initiated Indoor Air Chemistry
Evaluation of a Smoking Ordinance in Austin, TX
Sorptive Interactions between Volatile Organic Compounds and Indoor Materials
Shelter-In-Place during Extraordinary Events
The Effects of Indoor Materials on Building Disinfection
Architectural Coatings in Buildings: Fate and Human Exposure
Near Head Chemistry
The Effects of HVAC Filters on Indoor Ozone
Texas Elementary School Indoor Air Study (TESIAS)
Impact of Engine Retrofits on Indoor Air Quality on School Busses
The Effects of Vacuum Cleaning on Indoor Contaminated Carpet
HVAC Filter Bypass
Particle Transport in HVAC Systems
Particle Resuspension from Indoor Surfaces
Volatilization of Chemicals from Drinking Water to Indoor Air
Energy Implications of Filters in Residential and Light Commercial Construction
HVAC filters are the most common means of protecting building occupants and equipment from particles. Conventional wisdom suggests that a high pressure drop filter will use more energy, but this may not be true in most residential and light commercial impacts because of the interaction of pressure drop and fan and air conditioner energy consumption, duct leakage, and system capacity. To explore this, we are conducting a two-year field study of energy usage in 17 homes and small businesses in Austin. The study consists of monthly measurements of system energy usage, flow, filter pressure drop, and system capacity with different efficiency filters installed. We are also conducting additional measurements in the UTest House. The result of this investigation will allow homeowners to accurately trade off the benefits and costs of filtration.
Exposure to Toxic Air Contaminants
Recent data collected as part of the RIOPA study suggests that Mexican-Americans in the Houston area are exposed to more indoor pollution than White-Americans. This higher exposure likely leads to a higher risk of cancer. In collaboration with Dr. Maria Morandi at the UT Health Science Centers - School of Public Health (lead on project), IGERT trainees and faculty are helping to analyze personal, indoor, and outdoor VOC and aldehyde concentration data from two communities in the Houston area, one located in an industrial area. The goal of the research is to explore associations between personal concentrations of different VOCs and consumer product use and building characteristics, within the context of socioeconomic and ethnic differences in these variables.
HVAC Filters as Passive Samplers
HVAC filters are present in any building with a central conditioning system. They are an untapped resource for exploring occupant exposure to particle-bound contaminants. In this investigation, we are analyzing the dust on filters from a number of buildings and using state of the art techniques to assess heavy metal, fungal, bacterial, and spore concentrations. Comparisons of these data to air and surface dust concentrations suggest that this approach is a robust method of examining integrated concentration data. Ongoing work attempts to link the filter efficiency to the particle size distribution captured on the filters. This may provide new methods to explore sources and indoor occupant exposure.
The Role of Surfaces in Secondary Organic Aerosol Formation
Measurements of particle formation from the use of ion generators in a residential environment suggests that surfaces can change the number and size of particles formed. An ozone-reactive surface can diminish the amount of ozone available to form aerosol. However, a reactive surface that forms semi-volatile byproducts can enhance particle formation and/or growth by condensation on existing particles. We are currently investigating these reactions in laboratory chambers and are attempting to characterize the role of specific surface parameters.
p-Dichlorobenzene in Homes: Sources and Risks
p-Dichlorobenzene (p-DCB) is a USEPA Group C carcinogen and classified as a known carcinogen by the State of California. Recent studies show that amongst common volatile organic compounds (VOCs) found indoors, p-DCB is the only one to cause significant short-term decreases in pulmonary function. Children generally have significantly higher blood levels of p-DCB than adults living in similar households. Major sources of p-DCB in homes include moth repellents and deodorizers. The composition of these sources is generally close to pure p-DCB. In this study we combine field measurements, laboratory experiments, and mathematical modeling to explore cancer risks associated with p-DCB exposures in a wide range of residential scenarios. Laboratory experiments involve analyses of several different products (closet air freshener, moth crystals, toilet deodorizer, and moth “cases”) placed in different home and laboratory locations. Emissions are measured by gravimetric changes in the product over time. To date, emission rates have varied from less than 50 mg/hr (garment bag) to greater than 3,000 mg/hr (fume hood), with most typical indoor values on the order of 100 to several hundred mg/hr. Using conventional risk assessment protocols we predict cancer risks that are often in the hundreds to thousands per million, with a worst-case scenario of 30,000 in a million (3%) in a home with three closet air fresheners and two toilet deodorizers composed of pure p-DCB.
Near-Source Exposures to Toxic Air Contaminants in Cleaning Products
Many cleaning products contain volatile inorganic and/or organic chemicals that are irritating and/or toxic. The close proximity to these products during use can lead to elevated concentrations in the breathing zone of those who use the products. Exposures may be significant for those who clean for a living and use such products on a daily basis. We are studying the combined effects of source emission dynamics (mass transfer of chemicals from products to air) and fluid mechanics on human exposure to cleaning product chemicals. The study involves a combination of mathematical modeling, computational modeling, and experiments in large chambers and a full-scale test house (UTest House). Significant effort is being placed on the measurement of near continuous concentrations in the breathing zone, and selection of pure chemicals that can serve as surrogates for complex product mixtures.
Passive Removal of Ozone from Buildings
Most ozone exposure occurs indoors even though some surfaces consume ozone and reduce its concentration relative to outdoors. Ozone consumption often results in emissions of secondary pollutants. But materials such as gypsum board and activated carbon show promise as ozone removers without the concomitant generation of oxidized organic contaminants. In this study, we are evaluating activated carbon and bare drywall as passive ozone control surfaces in a room-sized laboratory chamber. Preliminary results indicate mean deposition velocities of 2.4 m hr-1 for gypsum board and 5.3 m hr-1 for activated carbon. The deposition velocity was measured at two mean air velocities of 0.1 and 0.19 m s-1 and over a relative humidity range of 25 to 55%. Gypsum board’s reactivity had no dependence on the relative humidity. An increase in relative humidity, from 20-50%, resulted in increased reactivity for activated carbon. In our model for a typical house, about 35% of the wall space would need to be replaced with unpainted gypsum board, or 12% with activated carbon to reduce ozone concentrations by 50%.
The Chemistry and Biology of Green Building Materials
Many building materials are often classified as being “green”, without a scientific or generally accepted definition of the meaning of this term. Nevertheless, there is a rapidly expanding market for such materials. Green building materials are intended to be environmentally friendly, with such characteristics as low toxicity, minimal chemical emissions, ability to be recycled, and durability. In addition, green materials often contain recycled and/or bio-based contents. Consequently, some green materials may undergo significant reactions with ozone, thus reducing indoor ozone concentrations. However, reactions between ozone and green materials may also produce secondary products that are subsequently emitted from the materials. In this study, 48L electro-polished stainless steel chambers were used to study the reactive consumption by ten common green wall, flooring, ceiling, and cabinetry materials (ceiling tile, unglazed ceramic tile, natural cork wall-paper, aluminum tinted cork wall-paper, bamboo, UV-coated bamboo, wheat board, UV-coated wheat board, sunflower board, and UV-coated sunflower board). Ozone removal was quantified in terms of cumulative molar consumption, deposition velocity, and reaction probability. Ozone removal decreased with time after initial exposure, but for several materials the ability to react with ozone was regenerated after a period of zero ozone exposure. Test materials with the highest ozone reaction probabilities were perlite-based ceiling tiles, natural cork wall-paper, and wheat board. Studies are now continuing to determine water isotherms for 14 green materials, and to also determine the susceptibility of these materials to mold growth upon wetting.
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Effective Positioning of Portable Air Cleaning Devices in Multizone Residential Buildings
An advantage of portable air cleaners is that they can be positioned in different parts of a building and used when air cleaning is needed. This makes them a very popular choice for use in residential buildings. In typical indoor particle modeling efforts, perfect air mixing and uniform contaminant concentration distribution is assumed. However, the use of portable air cleaners in buildings with open doors and particle circulation between rooms causes nonuniform spatial concentrations. In this study we analyze the overall contaminant removal in a multi-room residential building with non-uniform concentration of particulate contaminants and different portable air cleaners. Using validated computational fluid dynamic simulations we analyzed different: particle sizes, clean air delivery rates (CADR) of the air cleaner, and positions of portable air cleaner in the house. Our 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 several order of magnitude increase in the overall particle removal.
Analysis of Spatial and Temporal Pollutant Dispersion in Residential Buildings
The distribution of airflow in a residential building varies with periodic operation of a heating, ventilating and air-conditioning (HVAC) system. Depending on the HVAC fan operation, mixing airflow (fan ON) or stratified airflow (fan OFF) can occurs in the space. The study investigated the time needed for room air to stabilize after a central ventilation fan turns ON/OFF and evaluated how the difference in distribution of gaseous and particulate pollutants in the space depends on fan operation mode. The study results indicate that the transition between mixing flow and stratified flow occurs in a time scale of seconds, implying that the airflow in residential buildings is primarily mixing or stratified flow. We find very little spatial variation of gaseous and particulate pollutants with the mixing flow regime, whereas larger temporal and spatial variations are present with the stratified flow in the space. In certain areas of the room the particle concentration with buoyancy driven flow is up to order of value higher than that with mixing flow, implying a high potential of human exposure.
Transport of Particulate and Gaseous Pollutants in the Vicinity of a Human Body
A uniform pollutant concentration in indoor environments, used in many simplified human exposure studies, is often an inappropriate representative of the pollutant concentration inhaled by an occupant. We analyzed intensity of occupant thermal plume and non-uniform pollutant distribution around human body considering: breathing, hand movements, and mechanical fan operation. Results show that breathing affects intensity of an occupant thermal plume, while the localized hands motion does not disrupt significantly the upward airflow caused by thermal plume. Relatively uniform concentration patterns of gaseous and particulate pollutants in occupant vicinity were observed with highly mixed airflow in the space, whereas non-uniform concentration patterns were present in stratified flow. The finding implies that the occupant thermal plume can play a significant role in transporting resuspended particles from floor to breathing zone. The non-uniform concentration with stratified airflow also implies that applying “well-mixed” mass balance model to environments with low air mixing may lead to inaccurate estimation of exposure.
Development of Internal Surface Convection Correlations for Energy Calculations and Indoor Environment Modeling
It is important that energy and load calculation programs as well as indoor environment modeling tools accurately calculate convective heat fluxes on internal surfaces. The sensitivity of the overall heat transfer model to the applied internal convection correlation has been proven to be large. The variation of surface convection coefficients in the range that can be found in the indoor environment can create a difference in cooling load calculation of up to 27% and error in energy calculation of approximately 8%. Also, accuracy of air and pollutant flow modeling tools such as Computational Fluid Dynamics (CFD) heavily depends on the thermal boundary condition calculation. Therefore this project has a goal to provide engineering and research community with critical building design parameter in the form of improved convection coefficients. The developed convection correlations will be developed for integration into heating and cooling load calculation tools, energy simulation software, and CFD models for thermal boundary conditions calculation using experiment based wall functions.
Indoor Air Quality Implications of Portable Ion Generators
Ion generators are enormously popular air cleaners, despite the fact that scientific research and consumer advocate evaluation suggest caution in their use. Most ionizers generate ozone and have relatively low clean air delivery rates (CADRs). We have measured the clean air delivery rates and ozone emission rates for several portable ion generators. Our recent research has expanded these measurements to include CADRs for ultrafine particles (10-100 nm), a size range of importance for human health. We have also conducted measurements on ultrafine particle formation that can result from the use of ion generators. Our results suggest that ion generators are insufficiently effective for removing particles in typical indoor environments, generate enough ozone to be of concern, and can generate particles when used in the presence of an air freshener or other source of ozone-reactive compounds. These results beg the question of whether ion generators should ever be used in indoor environments.
Ozone-Initiated Indoor Air Chemistry
Ozone that penetrates through building envelopes or that is emitted from some indoor sources can react with a wide range of volatile organic compounds that originate indoors. Resulting by-products may be or greater concern than the reactants themselves, and include multi-functional oxygenated gases (carbonyls, acids, alcohols) as well as heavily oxygenated and ultra-fine secondary organic aerosols (SOA). We have completed both laboratory chamber and field studies to quantify the role of ozone-initiated indoor air chemistry on the formation of indoor SOA. Our experiments confirm that substantial amounts of indoor SOA can form, particularly in the presence of some scented consumer products that contain terpenes and terpene alcohols. We were the first group to apply a sophisticated outdoor atmospheric chemistry model to predict indoor homogeneous chemistry, including particle formation. The model (ICEM - Indoor Chemistry and Exposure Model) remains a valuable tool for research at UT.
Evaluation of a Smoking Ordinance in Austin, TX
On September 1, 2005, the City of Austin instituted a smoking ban that prohibits smoking in all public places, including bars and restaurants. This ordinance was very politically charged because Austin's identity is very closely tied to the live music scene and bar owners fear a loss of business. We measured several indoor air quality parameters in 17 bars before and after the ban and found significant reductions in all measured parameters after the ban in all compliant venues. We also found no significant difference between occupancy before and after the ban. Our results are very consistent with similar studies from around the world, and suggest that the smoking ordinance has been effective in reducing the exposure of patrons and workers.
Sorptive Interactions between Volatile Organic Compounds and Indoor Materials
Sorptive interactions between indoor air pollutants and indoor materials can lead to (1) a lowering of building occupant exposures to pollutants during source events, (2) an increase in occupant exposures after source events, and (3) contamination of indoor materials. We have completed and are continuing several major research projects aimed at better understanding the fundamental nature of interactions between indoor volatile organic compounds (VOCs) and a wide range of building materials. Our studies have involved the development of a wide range of experimental systems to determine adsorption and desorption rates, equilibrium partition coefficients, and chemical diffusion coefficients into materials. Two over-riding objectives of our research are (1) to improve estimates of the role of indoor materials on human exposure to everyday pollutants in buildings, as well as exposure in the event of extraordinary events such as release of chemical warfare agents, and (2) to identify ways in which architectural materials can be used for the improvement of indoor environmental quality, e.g., by removing and sequestering indoor pollutants.
Shelter-In-Place during Extraordinary Events
We have used our large source chambers to test a range of portable air purifiers for the removal of particles from indoor spaces. The effectiveness of these devices is compared in terms of a Clean Air Delivery Rate (CADR) that combines both the efficiency of particle removal through the device and the air flow rate through the device. With this knowledge we have employed mathematical models to estimate the effectiveness of portable HEPA filtration systems for indoor "shelter-in-place" during extraordinary events such as industrial accidents or outdoor releases of biological warfare agents.
We have also conducted field experiments that measure the effectiveness of shelter-in-place in residential and industrial buildings.
The Effects of Indoor Materials on Building Disinfection
The contamination of several buildings with Bacillus anthracis during the Fall of 2001 lead to a major push to better understand how to rapidly and effectively disinfect large indoor spaces. Furthermore, similar technologies are now being employed in homes, schools, office buildings and other spaces contaminated with mold and other biological contaminants. We completed the first and largest study of the effects of indoor materials on the removal of gas-phase building disinfecting agents such as chlorine dioxide, ozone, hydrogen peroxide, and methyl bromide. Twenty-four building materials were tested in laboratory chambers and quantified in terms of their reactivity with building disinfectants. Importantly, building disinfection by-products and their persistence were also identified for the first time, allowing planners to use this new information for purposes of building re-occupation planning after disinfection. We developed a novel software package called DADS (Disinfecting Agent Decision Support) software to assist those charged with planning building disinfection events as well for back-calculating possible target chemicals that lead to post-disinfection complains by building occupants. Several papers stemming from this research are currently under review.
Architectural Coatings in Buildings: Fate and Human Exposure
Over 500 million gallons of interior architectural coatings are produced in the United States each year. These coatings serve many beneficial purposes, but are also a source of indoor volatile organic compounds. We have done research to better understand emissions of two major components of most indoor latex paints: Texanol ester alcohol (TEA) and ethylene glycol (EG). Importantly, our research related to TEA has extended to emissions over nearly two years, and we have been the first team to do a complete mass closure assessment to show that TEA not emitted from gypsum wallboard is indeed still found within the wall board over long periods of timing after painting. We have tested several substrates, including aluminum, gypsum board, plywood, concrete, and stucco. We have also developed models to explore human exposure to TEA and EG during and after painting events.
Near Head Chemistry
Most perfume, colognes and other scented personal care products contain chemicals that are highly reactive with ozone. The reaction kinetics between ozone and several of these chemicals are so fast as to be relevant on time scales as short as air movement through the human breathing zone. This is important given that many of the reaction products between ozone and these fragrances are known to be irritating and potentially harmful. We were the first to do research on, and coin the terms, "near head chemistry" and "personal reactive clouds". Research is continuing to quantify relevant reaction products, develop sophisticated computational models for chemistry in the near head region, and explore the possibility of product reformulation to reduce risks to users of these products.
The Effects of HVAC Filters on Indoor Ozone
Filters are an integral part of most heating, ventilating and air conditioning (HVAC) systems, and can protect downstream HVAC components as well as remove some particulate matter from indoor air. We have been studying the effectiveness of conventional residential and commercial HVAC filters as control devices for ozone, as well as the potential for by-product formation and release following ozone reactions with these filters. A large number of new and used (mailed to UT from all over the country) HVAC filters have been tested in a new experimental filter testing system at UT. We are also currently testing an activated carbon-based filter which appears to hold great promise for reducing human exposure to ozone in indoor environments. Our studies should lead to advancements in knowledge related to the role of HVAC filters on indoor air quality, as well as the possibility of new filter designs to improve indoor environments.
Texas Elementary School Indoor Air Study (TESIAS)
Several reports in northern Europe have suggested classroom environments often have poor indoor air quality. We completed a large study to identify the state of indoor environmental quality in elementary schools in Texas. Two school districts were selected for study, one in Central Texas and one along the Texas/Mexico border. Written surveys were completed by over 900 teachers and air monitoring was completed in 240 classrooms randomly selected in the two districts. Our results indicated a general problem of poor ventilation in classroom environments leading to extensive and bothersome odors, an extraordinary use of air freshening devices that lead to elevated levels of volatile organic compounds in classrooms, relatively high levels of dichlorobenzene used as a deodorizing agent, and evidence of poor HVAC maintenance and construction related water leakage and mold problems. Over the years we have strived to assist schools with indoor air quality measurements and the development of internal low-cost measures for improving indoor air quality.
Impact of Engine Retrofits on Indoor Air Quality on School Busses
Millions of American children ride diesel school busses every day. There has recently been concern about the exposure to engine emissions that occurs on school busses. We are measuring several indoor air quality pollutants (e.g. NOx, CO, CO2, PM2.5, ultrafine PM, TVOCs) and bus parameters (e.g. air exchange, speed, engine operation) on 6 busses before and after engine retrofits. We hope that this research will provide data to decision-makers on the potential human exposure benefits of retrofits.
The Effects of Vacuum Cleaning on Indoor Particulate Matter Concentrations and Removal of Lead from Contaminated Carpet
Many indoor pollutants (both gases and particles) are removed from air by carpet. This can be beneficial in terms of reduced human exposure to airborne contaminants. However, contaminated carpet can also serve as a reservoir for contaminants that can increase human exposure via contact, e.g., hand-to-mouth exposure of small children, or that can be re-suspended to air via mechanical agitation, e.g., foot traffic or vacuuming. We have done large chamber experiments to test the effectiveness of vacuum cleaning technologies from lead-contaminated carpet, including carpets removed from actual buildings and carpets that we intentionally contaminated with fresh lead-based paint chips in our laboratory. Extensive laboratory analyses were completed to assess lead levels in air, carpet, and vacuum cleaner components. Our findings suggest that aged lead is very difficult to remove from carpet, but that freshly deposited lead can be removed effectively. We have also done extensive field studies to monitor particle concentrations in apartments before, during and after vacuuming events. Our results indicate highly elevated levels of particulate matter less than 10 microns in diameter in room air during and for several hours after vacuuming, suggesting the importance of not having individuals with dust allergies present during such events.
HVAC Filter Bypass
As consumers and building operators spend more on high-efficiency HVAC filtration, the installation of filter material becomes critically important. Higher-efficiency filters tend to have higher pressure drops and thus any unsealed gaps around the filter can lead to significant degradation of filter performance. We have performed extensive modeling of particle transport through the gaps around filters and the results suggests that even a small gap can noticeably degrade the performance of filters. We are conducting experiments to validate these results.
Particle Transport in HVAC Systems
HVAC systems are a central component of most buildings. We have conducted extensive simulations and measurements on particle transport and deposition on cooling and heating coils, filters, and duct surfaces. We are assembling this work into a cohesive model that can be used for determining sensor location, predicting cleaning and maintenance schedules, informing human exposure models.
Particle Resuspension from Indoor Surfaces
HVAC systems are a central component of most buildings. We are conducting detailed measurements to assess the relationship between particle resuspension and other factors such as surface roughness, particle size, air relative humidity, air velocity, turbulence intensity for real indoor materials. Our goal is provide data that will inform human exposure as well as provide information on cleaning and decontamination of indoor surfaces.
Volatilization of Chemicals from Drinking Water to Indoor Air
We have completed the most extensive set of experiments related to the transfer of chemicals from drinking water to indoor air. This research is relevant to chemicals ranging from radon and organic contaminants in groundwater to disinfection by-products in chlorinated potable water. Experiments were completed in a large stainless steel source chamber and included the determination of fundamental liquid and gas-phase mass transfer coefficients for a range of tracer chemicals emitted from showers, bathtubs, kitchen sinks, dishwashers, and washing machines. Additional experiments were completed to determine by-products from reactions between chlorine in dishwasher detergents and food left on plates and utensils in dishwashers.
