Pilot-Scale Demonstration of an Innovative Treatment for Vapor Emissions

ABSTRACT

Researchers from the National Renewable Energy Laboratory recently conducted a pilot-scale study at McClellan Air Force Base (AFB) in Sacramento, CA. The objective of the test was to determine the effectiveness of an ambient-temperature, solar-powered photocatalytic oxidation treatment unit for destroying emissions of chlorinated organic compounds from an air stripper. This paper reports test results and discusses applications and limitations of the technology.

A 10-standard-cubic-foot-per-minute (SCFM) (28.3 L/min) slip stream of air from an air stripper at Operative Unit 29-31 at McClellan AFB was passed through a reactor that contained a lightweight, perforated, inert support coated with photoactive titanium dioxide. The reactor faced south and was tilted at a 45° angle from vertical so that the light-activated catalyst received most of the available sunlight. An online portable gas chro-matograph with two identical columns simultaneously analyzed the volatile organic compounds contained in the reactor inlet and outlet air streams. Summa canister grab samples of the inlet and outlet were also collected and sent to a certified laboratory for U.S. Environmental

Protection Agency Method TO-14 analysis and verification of our field analyses. Three weeks of testing demonstrated that the treatment system's destruction and removal efficiencies (DREs) are greater than 95% at 10 SCFM with UV intensities at or greater than 1.5 milliwatts/square centimeter (mW/cm²). DREs greater than 95% at 20 SCFM were obtained under conditions where UV irradiation measured at or greater than 2 mW/cm². In Sacramento, this provided 6 hours of operation per clear or nearly clear day in April. A solar tracking system could extend operating time. The air stream also contained trace amounts of benzene. We observed no loss of system performance during testing.     

Construction and Economics of a Pilot/Full-Scale Biological Trickling Filter Reactor for the Removal of Volatile Organic Compounds from Polluted Air

ABSTRACT

The design and the construction of an actual 8.7-m³ pilot/ full-scale biotrickling filter for waste air treatment is described and compared with a previous conceptual scale-up of a laboratory reactor. The reactor construction costs are detailed and show that about one-half of the total reactor costs ($97,000 out of $178,000) was for personnel and engineering time, whereas ~20% was for monitoring and control equipment. A detailed treatment cost analysis demonstrated that, for an empty bed contact time of 90 sec, the overall treatment costs (including capital charges) were as low as $8.7/1000 m³ _air in the case where a nonchlorinated volatile organic compound (VOC) was treated, and $14/ 1000 m³ _air for chlorinated compounds such as CH₂Cl₂. Comparison of these costs with conventional air pollution control techniques demonstrates excellent perspectives for more field applications of biotrickling filters. As the specific costs of building and operating biotrickling filter reactors decrease with increasing size of the reactor, the cost benefit of biotrickling filtration is expected to increase for full technical-scale bioreactors.     

Black Carbon Aerosol at McMurdo Station,Antarctica

ABSTRACT

Aerosol light absorption as black carbon (BC) was measured from November 19, 1995, to February 6, 1996, at a location 0.65 km downwind of the center of McMurdo Station on the Antarctic coast. The results show a bimo-dal frequency distribution of BC concentrations. Approximately 65% of the measurements were found in a mode at a low range of concentrations centered at ~20 ng/m³. These concentrations are higher than those found at other remote Antarctic locations and probably represent contamination from the station. The remaining measurements were in a high-concentration mode (BC ~300 ng/m³), indicating direct impact of local emissions from combustion activities at the station. High values of BC were associated with winds from the direction of the station, and the BC flux showed a clear directionality. Maximum BC concentrations occurred between 7:00 and 11:00 a.m. The "polluted" mode accounted for more than 80% of the BC frequency-weighted impact at this location.     

A 13-Week Comparison of Passive and Continuous Ozone Monitors at Forested Sites in North-Central Pennsylvania

ABSTRACT

Ogawa passive O₃ samplers were used in a 13-week study (June 1-September 1, 1999) involving 11 forested and mountaintop sites in north-central Pennsylvania. Four of the sites were collocated with TECO model 49 O₃ analyzers. A significant correlation (p < 0.0001) was found for 24-hr average weekly O₃ concentrations between the two methodologies at the four sites with collocated monitors. As expected, there were positive relationships between increasing elevation of the sites and increasing O₃ concentrations. No O₃ exposure patterns were found on a west-to-east or south-to-north basis; however, the area known for lower O₃ exposures within a smaller subsection of the study area showed consistently lower O₃ exposures. Preliminary results regarding relationships of symptom responses within O₃-sensitive bioindicators are also presented with black cherry (Prunus serotina, Elirli.) and common milkweed (Asclepias syriaca, L.) showing clear evidence of increasing injury with increasing O₃ exposures. Due to the extremely dry conditions encountered in north-central Pennsylvania during the 1999 growing season, O₃-induced symptoms were sporadic and quite delayed until late-season rains during the latter portion of the observation period.     

Laboratory and Field Evaluation of Measurement Methods for One-Hour Exposures to O3, PM25, and CO

ABSTRACT

While researchers have linked acute (less than 12-hr) ambient O₃, PM₂₅, and CO concentrations to a variety of adverse health effects, few studies have characterized short-term exposures to these air pollutants, in part due to the lack of sensitive, accurate, and precise sampling technologies. In this paper, we present results from the laboratory and field evaluation of several new (or modified) samplers used in the “roll-around” system (RAS), which was developed to measure 1-hr O₃, PM₂₅, and CO exposures simultaneously. All the field evaluation data were collected during two sampling seasons: the summer of 1998 and the winter of 1999.

To measure 1-hr O₃ exposures, a new active O₃ sampler was developed that uses two nitrite-coated filters to measure O₃ concentrations. Laboratory chamber tests found that the active O₃ sampler performed extremely well, with a collection efficiency of 0.96 that did not vary with temperature or relative humidity (RH). In field collocation comparisons with a reference UV photometric monitor, the active O₃ sampler had an effective collection efficiency ranging between 0.92 and 0.96 and a precision for 1-hr measurements ranging between 4 and 6 parts per billion (ppb). The limits of detection (LOD) of this method were 9 ppb-hr for the chamber tests and ~16 ppb-hr for the field comparison tests.

PM_2.5 and CO concentrations were measured using modified continuous monitors—the DustTrak and the Langan, respectively. A size-selective inlet and a Nafion dryer were placed upstream of the DustTrak inlet to remove particles with aerodynamic diameters greater than 2.5 um and to dry particles prior to the measurements, respectively. During the field validation tests, the DustTrak consistently reported higher PM_2.5 concentrations than those obtained by the collocated 12-hr PM_{2 5} PEM samples, by approximately a factor of 2. After the DustTrak response was corrected (correction factor of 2.07 in the summer and 2.02 in the winter), measurements obtained using these methods agreed well with R² values of 0.87 in the summer and 0.81 in the winter. The results showed that the DustTrak can be used along with integrated measurements to measure the temporal and spatial variation in PM_{2 5} exposures. Finally, during the field validation tests, CO concentrations measured using the Langan were strongly correlated with those obtained using the reference method when the CO levels were above the LOD of the instrument [~1 part per million (ppm)].     

Wood Smoke Contribution to Winter Aerosol in Fresno,CA

Abstract

In an effort to better quantify wintertime particulate matter (PM) and the contribution of wood smoke to air pollution events in Fresno, CA, a field campaign was conducted in winter 2003–2004. Coarse and fine daily PM samples were collected at five locations in Fresno, including residential, urban, and industrial areas. Measurements of collected samples included gravimetric mass determination, organic and elemental carbon analysis, and trace organic compound analysis by gas chromatograph mass spectrometry (GC/MS). The wood smoke tracer levoglucosan was also measured in aqueous aerosol extracts using high-performance anion exchange chromatography coupled with pulsed amperometric detection. Sample preparation and analysis by this technique is much simpler and less expensive than derivatized levoglucosan analysis by GC/MS, permitting analysis of daily PM samples from all five of the measurement locations. Analyses revealed low spatial variability and similar temporal patterns of PM_2.5 mass, organic carbon (OC), and levoglucosan. Daily mass concentrations appear to have been strongly influenced by meteorological conditions, including precipitation, wind, and fog events. Fine PM (PM_2.5) concentrations are uncommonly low during the study period, reflecting frequent precipitation events. During the first portion of the study, levoglucosan had a strong relationship to the concentrations of PM_2.5 and OC. In the later portion of the study, there was a significant reduction in levoglucosan relative to PM_2.5 and OC. This may indicate a change in particle removal processes, perhaps because of fog events, which were more common in the latter period. Combined, the emissions from wood smoke, meat cooking, and motor vehicles appear to contribute ~65–80% to measured OC, with wood smoke, on average, accounting for ~41% of OC and ~18% of PM_2.5 mass. Two residential sites exhibit somewhat higher contributions of wood smoke to OC than other locations.     

Influence of Landscape Variability on Atmospheric Dispersion

Using idealized distributions of surface moisture, it is shown that with a significant synoptic prevailing flow over these regions of surface variability, dispersion is generally enhanced over heterogeneous surfaces as compared to horizontally homogeneous conditions. The importance of the heterogeneity becomes less, however, as the large scale wind speed increases and/or the spatial scale of the heterogeneities become less. This work also clearly demonstrates that the use of Gaussian regulatory models in areas of landscape variability is inappropriate.     

Mass transfer coefficients for volatilization of polychlorinated biphenyls from the Hudson River,New York measured using micrometeorological approaches

Air–water exchange is an important process controlling the fate of many organic chemicals in the environment. Modeling this process is hampered by the lack of direct observations. Thus, the purpose of this work was to derive direct measurements of the mass transfer coefficients for air–water exchange (v_aw) of polychlorinated biphenyls (PCBs) that may be used to check the validity of values derived from tracer gas experiments. v_aw values for PCBs were determined using previously published turbulent fluxes divided by the corresponding dissolved phase concentrations. The median v_aw values for each homolog decreased with increasing molecular weight and ranged from 0.29 for hexachlorobiphenyls to 2.2 m d^?1 for monochlorobiphenyls with a propagated uncertainty of about 70%, lower than in previous studies. Due to relatively low wind speeds and possible sorption of PCBs to colloids, these numbers may be biased low. These field measurements of v_aw differ by as much as a factor of 23 from predictions based on the widely-used Whitman two-film model. Therefore a new formulation for the calculation of v_aw based on field measurements is needed. This study demonstrates that micrometeorological approaches are a viable option for the measurement of v_aw for hydrophobic organics such as PCBs and should be used to generate enough field data on the air–water exchange of hydrophobic organics to allow the development of new predictive models.     

Are deep eutectic solvents benign or toxic?

In continuation of investigation for environmentally benign protocol for new solvents termed deep eutectic solvents (DESs), it is herein reported results concerning the toxicity and cytotoxicity of choline chloride (ChCl) based DESs with four hydrogen bond donors including glycerine, ethylene glycol, triethylene glycol and urea. The toxicity was investigated using two Gram positive bacteria Bacillus subtilis and Staphylococcus aureus, and two Gram negative bacteria Escherichia coli and Pseudomonas aeruginosa. The cytotoxicity effect was tested using the Artemia salina leach. It was found that there was no toxic effect for the tested DESs on all of the studied bacteria confirming their benign effects on these bacteria. Nevertheless, it was found that the cytotoxicity of DESs was much higher than their individual components (e.g. glycerine, ChCl) indicating that their toxicological behavior is different. For our best knowledge this is the first time that toxicity and cytotoxicity of DESs were studied. The toxicity and cytotoxicity of DESs varied depending on the structure of components. Careful usage of the terms non-toxicity and biodegradability must be considered. More investigation on this matter is required.