Browsing by Subject "volatile organic compounds"

Now showing 1 - 4 of 4
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    Activated Carbon Fibers from Cellulosic Biomass with Surface Reductive Treatment for Air Cleanup and VOCs Sensing
    (2018-12) Wang, Yu-Hsiang
    Biological volatile organic compounds (Bio-VOCs) play crucial roles in living organisms such as plants, microbes, and the animals. Sub-ppm level of Bio-VOCs could work as indicators to provide information about metabolism or hormones to facilitate different stages of growth in an organism. For example, less than 25 ppb of ethylene can reduce flowering time, increase seed weight and promote ripening of plants. Thus, there is a need for sensitive detection to provide valuable information for in situ monitoring of biological ecology, as well as for environmental controlling and managing. In situ monitoring of Bio-VOCs requires highly sensitive detections (at mostly sub-ppm concentration level) using portable and accurate sensors, which is extremely challenging for most analytical methods currently available. This work examines the feasibility of an intensified capture and detection strategy for detection of trace amounts of Bio-VOCs, with the sensor unit suitable for miniaturized design for eventually remote and unmanned vehicle sensing applications. In the first part of the study, activated carbon fibers were developed using a reductive reduction procedure, and were examined for pre-concentrating of Bio-VOCs (from ppb-level raised to ppm-level). We expect the reductive carbonization can effectively remove the oxygenated groups from the cellulosic materials, producing fine-tuned electronic properties, which promote pi-pi interaction for intensified the adsorption of nonpolar VOCs (especially for multiple pi bonds compounds). The such produced carbon fibers were examined by XPS (X-ray Photoelectron Spectroscopy), which showed that 53% of the carboxylic and hydroxy groups have been successfully removed. The performance of reductive treated carbon fibers as an adsorbent was examined. Three nonpolar VOCs, methane, ethylene and benzene, were selected as typical biological and chemical VOCs. A sixteen-times increase of benzene (has multiple pi bonds) adsorption can be observed in comparison to carbon fibers without reductive treatment. The unique network structure of the reductive treated carbon fibers also provides a fine electrical conductivity (6.36 Ωcm), that makes it possible for electrothermal desorption for material regeneration. A full regeneration of VOCs was observed in repeated adsorption-desorption cycles, indicating excellent reusability and stability of reductive carbonized carbon fibers. When applied as a pre-concentration absorbent, the carbon fibers successfully increased the concentration of typical VOCs from 500 ppb to 3.5 ppm (700% increase) within 20 min. In order to develop a miniaturized sensor with ultra-high sensitivity and stability for in situ monitoring of Bio-VOCs, the electrochemical sensing system was employed because it is able to identify and quantify various VOCs with high accuracy and sensitivity. However, most of traditional electrochemical sensors have been developed for analysis of aqueous samples, they are easily impacted by the evaporation of water (changing the concentration of electrolyte) when applied to gaseous samples as concerned in the current work. To improve the stability of electrochemical sensing, we developed a unique thin film ionic liquid (IL)-gel coated sensor employing ionic liquids in poly(acrylamide) hydrogels as a solution-free electrolyte. We assumed the stability of the analysis can be improved since the solution of the electrochemical system can be locked in a gel phase, minimizing the evaporation. The ion liquids also have been selected as an electrolyte since the acidity of IL can facilitate the detection of ethylene (one critical Bio-VOCs), preventing the oxidization of the working electrode before ethylene oxidization. A series of experiments were conducted to confirm the performance of IL-gel coating sensor. The results showed the sensor has excellent sensitivity and linearity of our sensor with low detection limit to 650 ppb and 0.99 of R2 values within 0~15 ppm. Decent stability was obtained with a relative standard deviation below 1% for 1.5 months of storage. In addition, the strategy of using reductive fabricated carbon fibers as a pre-concentrating material and a thin film IL-gel coated sensor as a detection unit was also examined. Overall, our work successfully demonstrated the capture-detection strategy is suitable for stable detecting of an extremely low (sub-ppb level) concentration of VOCs. By integrating the preconcentration and senor units, we could eventually develop sensors that are capable of detecting VOC samples in the order of ppb. This approach is promising for building up miniatured Bio-VOCs sensors for in situ monitoring in future applications.
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    Ecosystem-atmosphere fluxes of reactive carbon from the 2021 Flux Closure Study (FluCS) at Manitou Experimental Forest
    (2023-06-15) Vermeuel, Michael P; Millet, Dylan B; Farmer, Delphine K; Pothier, Matson A; Link, Michael F; dbm@umn.edu; Millet, Dylan B; University of Minnesota Atmospheric Chemistry Group
    This archive contains hourly observed and modeled fluxes of ambient volatile organic compounds (VOCs) over Manitou Experimental Forest in Woodland Park, CO during the FluCS 2021 study throughout August and September 2021. Observations were collected via the eddy covariance method using mass spectrometry for VOC concentrations and a sonic anemometer for vertical windspeed. Model fluxes were simulated using the GEOS-Chem (v13.3) model. Also included are observed and simulated meteorology during this time period.
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    Environmental Impact Of Beef Feedlot Cattle Feces, Urine, And Bedded Pack Facilities
    (2020-03) Jaderborg, Jeffrey
    Throughout the Upper Midwest, farmers have observed an increase in land prices and fertilizer prices resulting in the increased popularity of confinement feeding facilities such as mono-slope and hoop barns with bedded packs. Environmental and public pressure has been placed on the agriculture community to improve NH3, GHG, and VOC emissions from CAFOs. A study was conducted to determine the effect of bedding material (corn stover (CS), bean stover (BS), wheat straw (WS) or pine wood chips (PC)) and environmental ambient temperature (15°C (COLD) or 30°C (HOT)) on concentration of NH3, CH4, CO2, N2O, H2S, and odorous VOCs in air samples collected in headspace above lab-scaled bedded packs over a 42-d study. Bedded packs were housed in a common area at 18°C through Week 3 before being placed at their treatment temperature in respective environmental chamber. A significant (P = 0.0422) interaction between bedding material, ambient temperature and age of bedded pack was observed for CH4. Methane flux was similar across all treatments at Week 4. As bedded packs aged all the bedded packs in the cold chambers and the packs with the HOT-BS, HOT-PC, and HOT-WS treatment produced similar yet minimal flux compared to HOT-CS at Week 5. Whereas, at Week 6 HOT-BS and HOT-CS had significantly greater flux (10.48 and 12.59 mg m-2 hr-1; respectively) across all other treatments. A significant two-way interaction for bedding material by ambient temperature for NH3, H2S, and CO2, and N2O flux was observed (P = 0.0094, P < 0.0001, and P = 0.0005; respectively). Ammonia flux from BS, CS, and WS bedding material treatments was significantly greater at HOT ambient temperatures than COLD. Across all treatments significantly (P = 0.0407) greater NH3 flux (372.9 mg/m2/hr) was observed in headspace of HOT-WS bedded packs. Across all treatments COLD-BS had significantly (P < 0.0001) greater H2S flux than any other treatment, while bedding materials at HOT temperatures were similar. Carbon dioxide flux from WS bedding material was significantly (P < 0.05) greater no matter ambient temperature and increase over time. A significant (P = 0.0357) two-way interaction between ambient temperature and age of bedded pack for H2S flux was observed. Bedded packs maintained in COLD environments has similar H2S flux across weeks, while HOT treatments significantly (P = 0.0098) decreased from Week 4 to 6. Total aromatic compounds had significant (P = 0.0455) interaction for bedding material by ambient temperature as HOT were significantly greater than COLD across all bedding material types. An ambient temperature by age of bedded pack and bedding material by ambient temperature significant (P = 0.0008 and P = 0.0083)); respectively) interaction existed for total sulfide compounds as flux from COLD increase and HOT decrease over time. Total sulfides were the largest from PC bedded pack regardless of the temperature. Significant interactions for ambient temperature by age of bedded pack and bedding material by age of bedded pack was observed for both total BCFA and total SCFA. Total BCFA and total SCFA flux from CS and WS was significantly (P < 0.05) greater at Week 4, while total BCFA and total SCFA flux from HOT bedded packs decreased significantly (P < 0.05) from Week 4 to 5. Total OAVs decreases over time for both HOT and COLD treatments, although COLD treatments had significantly (P < 0.05) lower total OAVs regardless of age of bedded pack. Bedding types BS and PC had the lowest total OAV across all weeks. Aromatic compounds generated 72.0% of the total OAV over time. Producers should evaluate their bedded pack management system and consider potential bedding material being used and bedded pack removal frequency based on seasonal ambient temperatures to reduce overall operation flux emissions.
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    ROCRv2 methanol, ethene, ethyne, and HCN retrievals from the CrIS satellite sensor
    (2025-01-06) Wells, Kelley; Millet, Dylan; Brewer, Jared; dbm@umn.edu; Millet, Dylan; University of Minnesota Atmospheric Chemistry Group
    This archive contains new measurements of methanol, ethene, ethyne, and HCN from the CrIS satellite sensor, as well as the code developed for the figures in the following manuscript.