1,721,083 research outputs found
The measurement of the diffusion rates of volatile organic compounds through laboratory-prepared and intact soils.
No full textA device has been built, refined, and utilized to measure the fluxes of volatile organic compounds through laboratory-prepared soil cores and intact cores. The effective diffusion coefficients for VOCs in soils can be determined from steady state fluxes using Fick's First Law. Sorption characteristics can be estimated using kinetic information. The two compounds studied were trichloroethylene and benzene; the soil media tested were sand and glass beads at moisture contents ranging from 0 to 80% of water saturation. The temperatures tested were 10 to 25\sp\circC. Effective diffusion coefficients for each compound in soils with moisture contents of 20 to 50% closely matched the diffusion coefficients calculated with the Millington-Quirk equation. At higher moisture contents (e.g., 60-80%) the measured coefficients were 32.1 to 93.0% lower than the calculated coefficients, indicating the lack of applicability of the Millington-Quirk equation at high moisture contents. Completely dry media showed possible mass-transfer limitations as the measured coefficients were 3 to 19% lower than the calculated ones. Flux curves were modeled using the EPA's One Dimensional Finite Difference Vadose Zone Leaching Model (VLEACH). Using the experimentally determined soil porosity (), air-filled porosity (\rm\theta\sb{g}), and moisture content, the model was matched to the non-steady-state flux. With this fitting, the model was able to accurately predict the steady-state flux for that experiment. It was then shown that an experiment need not run to steady-state to estimate the final steady-state flux. This held for a variety of soil moisture contents and a variety of temperatures. Intact cores from a potentially contaminated site were examined but the results were unusable because the cores were irregular, had pulled away from the cylinder walls, and had large cracks, all indicative of soil moisture loss or other damage. The device nonetheless reached steady-state, indicating that for more well defined soil cores, the device would probably work as well as it did for laboratory-prepared cores. Improvements in methods and materials are suggested that would lead to more accurate results and thus better agreement between experimental and calculated results. Future possibilities for research with this device are the analysis of more than one compound at a time, having several devices doing analyses simultaneously, and obtaining a soil's characteristics on the basis of the non-steady-state and steady-state behavior of a well-characterized compound as it diffuses through that soil.PhDChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/105123/1/9635571.pdfDescription of 9635571.pdf : Restricted to UM users only
Identification and quantification of volatile organic compound emissions from buildings and heating, ventilating and air conditioning systems.
No full textMany indoor and outdoor sources release volatile organic compounds (VOCs) that can affect indoor air quality(IAQ). Indoor sources produce VOC concentrations in buildings that often greatly exceed outdoor levels. Since people spend 70-90% of their time indoors, most exposure to VOCs occurs indoors. This exposure is a potential contributor to the complex of sub-chronic health symptoms known as sick building syndrome. The objectives of this study were to characterize VOC emissions in buildings, to evaluate approaches for apportioning the emissions among major sources, and to explore relationships between VOC measurement techniques. VOC emissions from building materials and furnishings, occupants, and heating ventilation and air conditioning (HVAC) systems were estimated using a mass balance approach, measurements of total VOC (TVOC) concentrations using flame ionization detection, and speciated VOC (SVOC) measurements using canister samples, cryogenic preconcentration, gas chromatography and mass spectrometric detection. Three HVAC systems in two office buildings were tested over two seasons. Sorption characteristics of HVAC filters and filter dust were investigated separately in chamber tests. SVOC concentrations in the case study buildings ranged from 1.0 to 146 g/m\sp3, and TVOC levels ranged from 0.4 to 2.0 mg/m\sp3. The relationship between SVOC and TVOC levels depended on the VOC composition, sampling and analysis methods, and interested compounds in SVOC. Thus, while TVOC measurements are rapid and inexpensive, their usefulness as a screening tool appears to be limited. Occupants and their activities were important VOC sources in both buildings resulting in TVOC emissions of 2-3 g/hr during work hours. Building-related emissions were not significant in one building, but were much higher (6.1 g/hr) in the other building. These emissions appeared to result from building materials and printed matter stored in the building. Although some field measurements indicated strong sorption of toluene by HVAC filters and dust, this was not confirmed in laboratory chamber tests using toluene and trichloroethylene and these substrates. Sorption effects in HVAC systems may be more significant for low volatility compounds. Overall, HVAC emissions were not significant. The mass balance model using VOC measurements collected in HVAC systems can provide reliable estimates of indoor emissions if air in interior spaces is relatively well-mixed. The approach is especially suited to sealed buildings with single air handling systems. It provides building-wide estimates that apportion indoor concentrations to outdoor and several indoor sources, information that can be used to help improve IAQ.Doctor of Public Health (DPH)Applied SciencesCivil engineeringEnvironmental scienceHealth and Environmental SciencesPublic healthUniversity of Michigan, Horace H. Rackham School of Graduate Studies, School of Public Healthhttp://deepblue.lib.umich.edu/bitstream/2027.42/131370/2/9908032.pd
Formation, fate, and risks of disinfection by -products in foods and beverages.
No full textExposure to trihalomethanes (THMs), including CHCl3, CHCl 2Br, CHClBr2 and CHBr3, can occur by ingesting tap water containing disinfection by-products (DBPs) formed during water disinfection using chlorine. THMs are also present in meat, dairy products, vegetables, baked goods, beverages and other foods. This research addresses the formation, volatilization and sorption of THMs in foods and beverages, and the exposures and risks of THMs due to ingestion. Among tested beverages and foods, tea formed the highest THM levels (3--67 mug/L). In tea, CHCl3 formation increased with free chlorine concentration, decreased with tea concentration, and was unaffected by steeping time. Experiments designed to portray storage, pouring and serving of tap water and tea showed volatilization losses of THMs up to 90% for water and slightly less for tea, depending on water temperature and standing time. The adsorption of THMs on foods was tested at 25 and 90 C for a variety of foods. THM uptake depended on food type, preparation and concentration, temperature, and THM species and concentration. Screening tests yielded concentrations from 55--872 ng/g for cauliflower, tomato, mushroom, pepper, spinach, lettuce, celery and broccoli at 25 C, and from 32--1793 ng/g at 90 C for beans, carrots, corn, lima bean, cabbage, tomato, squash, potato, rice, chicken and beef. These concentrations are high relative to those in the literature because volatilization was excluded, foods were cut into small pieces, and initial THM concentrations were high. A plane sheet diffusion model matched experimental results for lettuce and spinach, and a spherical diffusion model matched results for tomato, potato and beef. Formation and volatilization processes were incorporated into an exposure assessment, after which cancer and non-cancer risks were evaluated. CHCl 3 and CHCl2Br risks from food and beverage ingestion were 3.7 and 0.4 times, respectively, higher than the risk resulting from tap water ingestion alone. Excess lifetime cancer risks from all ingestion sources for CHCl3, CHCl2Br, CHClBr2, and CHBr3 were 8.6, 7.7 and 2.3 and 0.32 x 10-6, respectively. Non-cancer risks, expressed as hazard quotients, were small. These results indicate the need to incorporate THM exposures from beverages and foods into epidemiological and risk studies.PhDAgricultural engineeringApplied SciencesBiological SciencesEnvironmental scienceFood scienceHealth and Environmental SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/124817/2/3163824.pd
Volatile organic compounds in industrial, urban, and suburban areas: Sources and exposures.
No full textThis research was aimed at evaluating and refining sampling and analytical methods for airborne volatile organic compounds (VOCs), and at characterizing concentrations and potential exposures of VOCs found in indoor and ambient air in industrial, urban and suburban communities. A new analytical strategy of combining selective ion monitoring (SIM) and scan mode mass spectrometer analyses was developed and evaluated. This strategy improved sensitivity and selectivity without extra cost or calibration efforts. An intermittent active sampling method for collecting VOCs, which has not been previously evaluated, was compared to continuous active and passive sampling methods with the aim of obtaining long-term integrated measurements. Results obtained by the three methods agreed over a wide concentration range after accounting for the sampling rate. Intermittent sampling provides greater flexibility with respect to sampling period and flow rate, and enables the use of multi-bed adsorbents that increase the range of VOCs that can be monitored. VOC concentrations were measured inside and outside of 159 residences in suburban (Ann Arbor), urban (Ypsilanti) and urban/industrial (Dearborn) communities in southeastern Michigan from 2004 to 2005. A total of 53 and 46 VOCs were detected indoors and outdoors, respectively. Outdoors, benzene, toluene, p,m-xylene and carbon tetrachloride had the highest concentrations, and differences were seen between cities and seasons. Factor analyses identified four types of outdoor sources: vehicle exhaust/gasoline vapor, industrial solvents, biogenic emissions, and industrial sources. Indoors, benzene, toluene, p,m-xylene, n-heptane, alpha-pinene and d-limonene had the highest concentrations. Indoor to outdoor concentration ratios ranged from 1 to 10 for most compounds. Higher indoor concentrations were associated with the presence of attached garages, recent renovations, indoor smoking, residence age, infrequent window/door opening, high CO2 concentration, lower ventilation, and community. Factor analyses identified up to ten VOC source types in residences. This is one of the most comprehensive VOC surveys conducted in the US since 2000. A semi-parametric probability framework was developed to characterize VOC mixtures in residences. High concentration VOC mixtures resulted from the presence of several features (e.g. strong sources and ventilation conditions), and many characteristics of the observed mixtures could be represented using multivariate and correlated lognormal distributions.PhDAtmospheric sciencesEarth SciencesEnvironmental scienceHealth and Environmental SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/126728/2/3276194.pd
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Measurement and characterization of particulate and bioaerosol pollutants in indoor air.
No full textSuspended particulate matter and bioaerosols are important indoor air quality (IAQ) contaminants that may have adverse health effects on building occupants. This study addresses the characterization of aerosol pollutants in large, mechanically ventilated buildings. Characterization of IAQ can be difficult in large buildings due to the inherent variability in distribution of particulate matter and bioaerosols, the many and diverse uses of interior spaces, changes in occupant activities over time, and the large and complex heating, ventilating and air conditioning (HVAC) systems. This study evaluates aerosol measurement methods, sampling strategies, and data interpretation techniques including source apportionment. Comprehensive field investigations in office and other buildings are used to evaluate these measurements, as well as mathematical and statistical models. Principal conclusions of the study include the following: Measurements of airborne and bulk (surface) concentrations of particulate matter in HVAC system ducts and components can complement measurements in the occupied zone and outdoor air and should be utilized in IAQ field investigations. Shrouded probe samplers are well suited to sampling in the flowing air streams of HVAC ducts and can eliminate the need for isokinetic sampling. Airborne bioaerosol concentrations in the HVAC system and occupied zone should be low (200 cfu m\sp{-3}). High microbial concentrations in bulk samples collected from HVAC systems may identify potential emission sources, however, this does not necessarily indicate that indoor air is significantly or frequently contaminated. Airborne concentrations of particulate matter in ducts can indicate the air quality delivered to occupants. Return air concentrations may not be representative of those found in indoor air although these measurements can be used to estimate HVAC system performance, e.g., ventilation effectiveness. To obtain representative results, sampling strategies should account for the autocorrelation of pollutant levels, air exchange rate, and ventilation effectiveness. Occupant activities can increase concentrations of larger particles and partly explain the variability of concentrations at certain locations. These conclusions are particularly applicable to particulate and bioaerosol measurements in large and mechanically ventilated office buildings.PhDApplied SciencesArchitectureCommunication and the ArtsEnvironmental engineeringEnvironmental scienceHealth and Environmental SciencesPublic healthUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/130771/2/9811135.pd
Filtration of ozone by carbonaceous materials: Removal efficiencies and reactions with volatile organic compounds.
No full textActivated carbon (AC) and other materials have been used widely in air filtration applications, including occupational respirators, room air and ventilation system filters, and vapor recovery systems. While carbonaceous materials are known to remove gases and vapors including ozone (O3) and volatile organic compounds (VOCs), the removal of O3 at environmental concentrations has not been well characterized. This research investigated whether removal efficiencies at low O3 concentrations could be predicted using tests conducted at high O3 concentrations, whether VOC loadings on filters affected O3 removal efficiency, and whether reactions between O3 and VOCs occurred heterogeneously on AC and produced emission products. Additionally, removal of O3 by diesel particulate matter (DPM), a significant contributor to the carbon aerosol in urban atmospheres, was evaluated. AC and DPM samples were exposed to O 3 in a flow-through experimental system, and filter effluents were monitored for O3, VOCs and other parameters. For virgin AC filters, O 3 removal rates varied by O3 concentration, bed mass and exposure time, and O3 removal capacities ranged from 2 to 43 wt % at 65 hr. Of four chemisorption models tested, the Elovich equation provided the best fit to breakthrough data. VOC-loaded filters differed in breakthrough behavior and were 5 to 25% less efficient at removing O3 than unloaded filters, attributed to poisoning by toluene and pseudo-poisoning by d-limonene. Gas- and condensed-phase compounds formed in homogeneous reactions between O3 and d-limonene included formic acid (molar yield of 37%), 4-acetyl-1-methylcyclohexene (4%), propanoic acid (3%) and limonene oxides (3%). Heterogeneous experiments using limonene-loaded AC filters showed formation of 4-acetyl-1-methylcyclohexene and limonene oxides, but only small quantities were emitted in filter effluent, and the bulk of the limonene remained unreacted on the AC even after exposure to a stoichiometric excess of O3. DPM-loaded filters removed 6 +/- 2 wt % of O 3, much less than that found for AC, and DPM is expected to remove only a small fraction of O3 from urban/tropospheric or indoor air. Overall, this research provides quantitative estimates of O3 removal by AC and DPM, information that can be used in the design and evaluation of air cleaning systems.PhDEnvironmental scienceHealth and Environmental SciencesPublic healthUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/124509/2/3150044.pd
The Case for Proactive Chemicals Management in REI Operations
Get PDFREI’s CSR framework involves seven environmental lenses: climate change, energy use, waste, water, chemicals, land use, and social impacts. REI currently measures, tracks, and systematically reduces its operations level impacts related to: (1) energy use, (2) waste-to-landfill, and (3) tons of CO2E emissions. The SNRE master’s project team worked with REI’s CSR team to define a strategy to address chemicals impacts within operations, and implement a robust management and reduction plan. Project objectives included:
1. Identify key chemicals impacts associated with REI’s operations;
2. Develop a business case for adoption of a company wide chemicals management strategy, to be presented to REI executives;
3. Identify aspirational long term reduction goals, and foundational interim milestones;
4. Define a metric for chemicals impact reduction, if applicable;
5. Prioritize organizational activities aimed at reducing chemicals management impacts;
6. Identify potential organizational barriers to adoption of the chemicals lens and strategies to mitigate or overcome those barriers.
The team used a combination of primary and secondary company and academic research to develop a business case and feasible, effective chemicals management strategy.
Master of Science (MS)Natural Resources and EnvironmentUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/97345/1/Case-for-Proactive-Chemicals-Management-REI_FINAL april 2013.pd
Indoor air quality and human health and comfort in large, mechanically ventilated office buildings: Longitudinal studies.
No full textThe objectives of this research were to investigate methods to assess indoor environmental quality and the health symptoms and perceptions of building occupants, and to utilize such measurements in epidemiological investigations aimed at understanding causes of sick building syndrome (SBS) and other sources of occupant complaints. Two experimental interventions and a longitudinal cohort investigation were used to study 49 workers on four floors of a large non-problem office building. Eight surveys addressing occupant health, comfort and perceptions of the indoor environment, including a comprehensive initial survey, were administered to study participants over a 17-month period. Simultaneously, indoor air quality parameters were measured using continuous and integrated sampling techniques. Interventions included cleaning the building's heating, ventilating and air conditioning (HVAC) systems, and distributing a document to participants describing the indoor environment. The longitudinal cohort study tested the association between symptomology and perceptions to HVAC operational modes. Continuous measurements of air quality provided useful trend and peak information, superior to that obtained in grab and integrated sampling. Several pollutants showed diurnal and/or weekly patterns that were correlated to indoor and outdoor emissions. Levels of bioaerosols, particulate matter, volatile organic compounds, ozone, carbon dioxide and nitrogen oxides fell below standards and guidelines. Many participants experienced SBS symptoms (e.g., 32% for eye symptoms, 12% headache) at rates similar to those found in other large building surveys. Operating the HVAC system in economizer mode (spring and fall), as compared to high recirculation (winter and summer), reduced some adverse health and comfort outcomes. However, changes were small and seasonal factors, among others, could not be completely controlled. No significant differences in symptoms and perceptions due to the information document or the cleaning intervention were observed, the latter possibly because contaminant levels were already low and not significantly altered. This study demonstrates methodological improvements for investigating the indoor environment and occupant health, including the use of continuous instrumentation to assess pollutant exposures, psychosocial stress measures (found to be a significant co-factor), repeated measures on occupants, and standardization of questionnaires. These and other recommendations should improve the understanding of the effect of the indoor environment on health and comfort.PhDApplied SciencesCivil engineeringEnvironmental scienceHealth and Environmental SciencesPublic healthUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/123390/2/3079450.pd
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