Total Mass Loading Research Articles

Real time measurement of chemical composition of submicrometer aerosols at urban Gwangju in Korea by aerosol mass spectrometer

Size-resolved chemical constituents (organics, sulfate, nitrate, ammonium, and chloride) of nonrefractory submicrometer particles were measured in real time using a quadruple aerosol mass spectrometer (QAMS) at an urban area of Gwangju, Korea in the fall (8/30/2011–9/19/2011) and winter (12/19/2011–12/30/2011). Organics were found to be the most dominant chemical species (∼50%) in the total aerosol mass loading. The average mass concentrations of organics were 4.7 ± 1.8 μg m−3 and 6.3 ± 1.8 μg m−3 in the fall and winter, respectively. The organics increased in the morning and evening times, and decreased in the afternoon in both the fall and winter, with a more pronounced diurnal pattern observed in the winter. The ratio of m/z 44 to organics and sulfate increased significantly in the afternoon, which is contrary to the behavior of the total organics, suggesting that intense photochemical activity led to the production of oxidized organics and sulfate in the afternoon. The average sulfate concentration was 1.8 μg m−3, which was the lowest reported in East Asian countries due to there being few SO2 emission sources around the sampling site. The most significant difference in concentrations between the fall and winter was found for nitrate; the concentration was ∼4 times higher than in the fall (2.45 μg m−3 versus 0.62 μg m−3). It was also observed that sulfate, nitrate, and chloride were fully neutralized by the ammonium in the winter, whereas these anions were not fully neutralized in the fall. Size distribution data showed that sulfate had only one Dva peak at 600 ± 100 nm, regardless of season, and that organics had one peak (600 ± 100 nm) in the fall and a bimodal distribution (200 ± 100 nm and 600 ± 100 nm) in the winter. The absence of the first mode (i.e., Dva ∼200 nm) in organics in fall and the higher ratios of m/z 44 to organics in fall (0.10 ± 0.02) than winter (0.07 ± 0.01) suggest that oxidized organic species would be more dominant than hydrocarbon-like organics. Air-mass dependent concentrations of species showed that the northwest air mass (i.e., long-range transported from industrial areas in China) and southeast air mass (i.e., transported from industrial area in Korea) were mainly responsible for the high loadings of organics and sulfate.

Tracing pharmaceuticals in a municipal plant for integrated wastewater and organic solid waste treatment

The occurrence and removal of 42 pharmaceuticals, belonging to different therapeutic groups (analgesics and anti-inflammatory drugs, anti-ulcer agent, psychiatric drugs, antiepileptic drug, antibiotics, ß-blockers, diuretics, lipid regulator and cholesterol lowering statin drugs and anti-histamines), were studied in the wastewater and sewage sludge trains of a full scale integrated treatment plant. The plant employs a biological nutrient removal (BNR) process for the treatment of municipal wastewater, and a single-stage mesophilic anaerobic co-digestion for the treatment of wasted activated sludge mixed with the organic fraction of municipal solid waste (OFMSW), followed by a short-cut nitrification–denitrification of the anaerobic supernatant in a sequential batch reactor. Influent and effluent wastewater, as well as thickened, digested and treated sludge were sampled and analyzed for the selected pharmaceuticals in order to study their presence and fate during the treatment. Twenty three compounds were detected in influent and effluent wastewater and eleven in sludge. Infiltration of groundwater in the sewer system led to a dilution of raw sewage, resulting in lower concentrations in wastewater (up to 0.7μg/L in influent) and sludge (70ng/g d.w.). Due to the dilution, overall risk quotient for the mixture of pharmaceuticals detected in effluent wastewater was less than one, indicating no direct risk for the aquatic environment. A wide range of removal efficiencies during the treatment was observed, i.e. <20% to 90%. The influent concentrations of the target pharmaceuticals, as polar compounds, were undoubtedly mostly affected by BNR process in the wastewater train, and less by anaerobic-co-digestion. Mass balance calculations showed that less than 2% of the total mass load of the studied pharmaceuticals was removed by sorption. Experimentally estimated distribution coefficients (<500L/kg) also indicated that the selected pharmaceuticals preferably remain in the aqueous phase, and that biodegradation/transformation is the primary removal mechanism for these compounds during wastewater treatment.

An ex situ evaluation of TBA- and MTBE-baited bio-traps

Aquifer microbial communities can be investigated using Bio-traps® (“bio-traps”), passive samplers containing Bio-Sep® beads (“bio-beads”) that are deployed in monitoring wells to be colonized by bacteria delivered via groundwater flow through the well. When bio-beads are “baited” with organic contaminants enriched in 13C, stable isotope probing allows assessment of the composition and activity of the microbial community. This study used an ex situ system fed by groundwater continuously extracted from an adjacent monitoring well within an experimentally-created aerobic zone treating a tert-butyl alcohol (TBA) plume. The goal was to evaluate aspects of bio-trap performance that cannot be studied quantitatively in situ. The measured groundwater flow through a bio-trap housing suggests that such traps might typically “sample” about 1.8 L per month. The desorption of TBA or methyl tert-butyl ether (MTBE) bait from bio-traps during a typical deployment duration of 6 weeks was approximately 90% and 45%, respectively, of the total initial bait load, with initially high rate of mass loss that decreased markedly after a few days. The concentration of TBA in groundwater flowing by the TBA-baited bio-beads was estimated to be as high as 3400 mg/L during the first few days, which would be expected to inhibit growth of TBA-degrading microbes. Initial inhibition was also implied for the MTBE-baited bio-trap, but at lower concentrations and for a shorter time. After a few days, concentrations in groundwater flowing through the bio-traps dropped below inhibitory concentrations but remained 4–5 orders of magnitude higher than TBA or MTBE concentrations within the aquifer at the experimental site. Desorption from the bio-beads during ex situ deployment occurred at first as predicted by prior sorption analyses of bio-beads but with apparent hysteresis thereafter, possibly due to mass transfer limitations caused by colonizing microbes. These results suggest that TBA- or MTBE-baited bio-traps could be baited at lower initial total mass loading with no detriment to trapping ability. The bio-traps were able to collect detectable amounts of microbial DNA and thus allow some insight into the sparse microbial community present in the aquifer during remediation of the low concentration plume.

The surface energy balance at the Huygens landing site and the moist surface conditions on Titan

The Huygens Probe provided a wealth of data concerning the atmosphere of Titan. It also provided tantalizing evidence of a small amount of surface liquid. We have developed a detailed surface energy balance for the Probe landing site. We find that the daily averaged non-radiative fluxes at the surface are 0.7Wm−2, much larger than the global average value predicted by McKay et al. (1991) of 0.037Wm−2. Considering the moist surface, the methane and ethane detected by the Probe from the surface is consistent with a ternary liquid of ethane, methane, and nitrogen present on the surface with mole fractions of methane, ethane, and nitrogen of 0.44, 0.34, and 0.22, respectively, and a total mass load of ∼0.05kgm−2. If this liquid is included in the surface energy balance, only a small fraction of the non-radiative energy is due to latent heat release (∼10−3Wm−2). If the amount of atmospheric ethane is less than 0.6×10−5, the surface liquid is most likely evaporating over timescales of 5 Titan days, and the moist surface is probably a remnant of a recent precipitation event. If the surface liquid mass loading is increased to 0.5kgm−2, then the liquid lifetime increases to ∼56 Titan days. Our modeling results indicate a dew cycle is unlikely, given that even when the diurnal variation of liquid is in equilibrium, the diurnal mass variation is only 3% of the total liquid. If we assume a high atmospheric mixing ratio of ethane (>0.6×10−5), the precipitation of liquid is large (38cm/Titan year for an ethane mixing ratio of 2×10−5). Such a flux is many orders of magnitude in excess of the photochemical production rate of ethane.

Assessing the diurnal variability of pharmaceutical and personal care products in a full-scale activated sludge plant

An intensive sampling campaign has been carried out in a municipal wastewater treatment plant (WWTP) to assess the dynamics of the influent pharmaceutical active compounds (PhAC) and musks. The mass loadings of these compounds in wastewater influents displayed contrasting diurnal variations depending on the compound. The musks and some groups of PhACs tended to follow a similar diurnal trend as compared to macropollutants, while the majority of PhACs followed either the opposite trend or no repeatable trend. The total musk loading to the WWTP was 0.74±0.25gd−1, whereas the total PhAC mass loading was 84.7±63.8gd−1. Unlike the PhACs, the musks displayed a high repeatability from one sampling day to the next. The range of PhAC loadings in the influent to WWTPs can vary several orders of magnitude from one day or week to the next, representing a challenge in obtaining data for steady-state modelling purposes.

Temporal variability of pharmaceuticals and illicit drugs in wastewater and the effects of a major sporting event

Diurnal variations in wastewater flows are common phenomena related to peak water use periods. However, few studies have examined high-resolution temporal variability in trace organic contaminant (TOrC) concentrations and loadings. Even fewer have assessed the impacts of a special event or holiday. This study characterizes the temporal variability associated with a major sporting event using flow data and corresponding mass loadings of a suite of prescription pharmaceuticals, potential endocrine disrupting compounds (EDCs), and illicit drugs. Wastewater influent and finished effluent samples were collected during the National Football League’s Super Bowl, which is a significant weekend for tourism in the study area. Data from a baseline weekend is also provided to illustrate flows and TOrC loadings during “normal” operational conditions. Some compounds exhibited interesting temporal variations (e.g., atenolol), and several compounds demonstrated different loading profiles during the Super Bowl and baseline weekends (e.g., the primary cocaine metabolite benzoylecgonine). Interestingly, the influent mass loadings of prescription pharmaceuticals were generally similar in magnitude to those of the illicit drugs and their metabolites. However, conventional wastewater treatment was more effective in removing the illicit drugs and their metabolites. Total influent and effluent mass loadings are also provided to summarize treatment efficacy and environmental discharges.

Soil aquifer treatment of artificial wastewater under saturated conditions

A 2000 mm long saturated laboratory soil column was used to simulate soil aquifer treatment under saturated conditions to assess the removal of chemical and biochemical oxygen demand (COD and BOD), dissolved organic carbon (DOC), nitrogen and phosphate, using high strength artificial wastewater. The removal rates were determined under a combination of constant hydraulic loading rates (HLR) and variable COD concentrations as well as variable HLR under a constant COD. Within the range of COD concentrations considered (42 mg L −1–135 mg L −1) it was found that at fixed hydraulic loading rate, a decrease in the influent concentrations of dissolved organic carbon (DOC), biochemical oxygen demand (BOD), total nitrogen and phosphate improved their removal efficiencies. At the high COD concentrations applied residence times influenced the redox conditions in the soil column. Long residence times were detrimental to the removal process for COD, BOD and DOC as anoxic processes and sulphate reduction played an important role as electron acceptors. It was found that total COD mass loading within the range of 911 mg d −1–1780 mg d −1 applied as low COD wastewater infiltrated coupled with short residence times would provide better effluent quality than the same mass applied as a COD with higher concentration at long residence times. The opposite was true for organic nitrogen where relatively high concentrations coupled with long residence time gave better removal efficiency.

Aluminum electrocoagulation pretreatment reduces fouling during surface water microfiltration

A bench-scale study was undertaken to evaluate aluminum electrocoagulation pretreatment for dead-end, constant pressure microfiltration of surface water. Electrochemical aluminum production quantitatively obeyed Faraday's law with a 3-electron transfer at nearly 100% efficiency resulting in Al(OH) 3 precipitation. X-ray diffractometry proved that Al(OH) 3 precipitates were predominantly amorphous. Enmeshment of colloids in amorphous precipitates (sweep flocculation) was the predominant colloid destabilization mechanism. Additionally, the floc zeta potential became less negative (→0) as more and more aluminum was added indicating the secondary role of adsorption of hydrolyzed aluminum species and charge neutralization in destabilization. Fouling of a commercially available polymeric microfiltration membrane following electrocoagulation pretreatment was found to (i) be lower at pH 6.4 compared with 7.5, (ii) decrease only up to an intermediate aluminum dosage, and (iii) exacerbate with increasing transmembrane pressure. In all experiments, cake filtration was the predominant flux decline mechanism for the entire duration of microfiltration. Increased fouling at higher transmembrane pressures (manifested as more rapid decline of the instantaneous flux normalized by the initial flux) was attributed to cake compressibility. Optical microscopy revealed that floc sizes increased monotonically with aluminum dosage even though fouling worsened at high electrocoagulant concentrations. This suggests that fouling was controlled by antagonistic effects of adding more and more aluminum coagulant; increasing total mass loading of colloidal foulants (higher total filtration resistance) and creating larger flocs (decreasing specific cake resistance). Significant reductions in microfilter fouling with aluminum electrocoagulation pretreatment suggests the next logical step of larger-scale testing under “real-world” conditions before recommending it for surface water treatment.

Perfluorinated compounds (PFCs) in Yodo River system, Japan

There is increasing concern about occurrences of perfluorinated compounds (PFCs) in the environment due to their persistent, bioaccumulation, and potentially toxic effects. We investigated contamination of 11 PFCs (C4-C12) in the Yodo River system, which is a major source of drinking water for more than 11 million people of Kansai region in Japan. PFCs were detected in higher concentration even exceeding more than 1000 ng/L in some cases. Composition profile of total PFCs concentration showed that PFOS, PFHxA, PFOA, and PFNA were occurring dominantly in the river system. PFOS and PFOA concentration were nearly proportional to a previous study in the same river system, indicating continuous sink of the compounds into the river system. Although discharge of PFCs from wastewater effluents at upstream could be one of the major point sources, concentration did not exceed 29.4 ng/L at the downstream of main Yodo River, possibly, due to dilution effects. Total mass load of PFCs in mainstream of Yodo River was estimated 451.7 g/d based on observed river discharge and PFCs concentration. Results showed that Yodo River system could have a unique upstream-downstream linkage of PFCs contamination and the river could be a continuous pathway of PFCs exposure to the people of Kansai region.

Source characterization of nervous system active pharmaceutical ingredients in healthcare facility wastewaters

Nervous system active pharmaceutical ingredients (APIs), including anti-depressants and opioids, are important clinically administered pharmaceuticals within healthcare facilities. This study provides source characterization data describing the composition and magnitude of nervous system APIs present in healthcare facility wastewaters. Concentrations and mass loadings of ten nervous system APIs and three nervous system API metabolites are reported for wastewaters from a hospital, nursing, assisted living, and independent living facility within a single municipality. Concentrations of nervous system APIs ranged from non-detectable levels for alprazolam in all four facility wastewaters to a high of 290 ng/L amitriptyline in nursing facility wastewater. The summed mean concentration of all thirteen analytes ranged from 402 ng/L in independent living facility wastewater to 624 ng/L in assisted living facility wastewater. Wastewater flow rates from each facility were combined with concentration data to estimate the daily mass loading of nervous system APIs leaving each facility through wastewater discharge to the municipal sewer system. The total mass loading of all thirteen analytes for the hospital, nursing, assisted living, and independent living facility was 228, 44, 29.5, and 28.1 mg/day, respectively. The total mass loading of nervous system APIs contributed to the municipality’s wastewater from all four facilities was 330 mg/day.

Quantifying Nutrients in Effluent from Uncovered, Intact Mature Bovine Carcass Compost Piles Subjected to Storm Events

Effluent pollutant concentrations and volumes were collected from uncovered, intact carcass, dairy cow mortality compost piles subjected to successive simulated 10.2 cm storm events after: (1) composting one cow in fresh sawdust only; (2) turning that pile, adding fresh amendment, adding a second cow, and composting it; and (3) turning the pile again, without an animal tissue addition. Phosphorus leaving an active mortality compost pile in runoff as produced by a 10.2 cm storm simulation ranged from 4.6 grams to 0.1 grams. Total COD in runoff ranged from 94 to 888 grams. Data indicated that the majority of nutrients in effluent leaving a pile from a 10.2 cm storm event infiltrate the soil surface. Total nitrogen mass load infiltrating the soil was estimated to range between 362 and 1778 grams under various management stages. With the exception of NO3, the nutrient concentrations in groundwater at 1.2 m soil profile depth were reduced by nine fold or more when compared to direct pile effluent, indicating that soil provided treatment of infiltrating pile effluent. No significant accumulation of soil nutrients below mortality compost piles occurred during the study. However, pile effluent nutrient characteristics indicate that soil nutrient accumulation may occur over time.

Near-infrared laser desorption/ionization aerosol mass spectrometry for measuring organic aerosol at atmospherically relevant aerosol mass loadings

Abstract. A new method, near-infrared laser desorption/ionization aerosol mass spectrometry (NIR-LDI-AMS), is described for the real time analysis of organic aerosols at atmospherically relevant total mass loadings. Particles are sampled with an aerodynamic lens onto an aluminum probe. A moderate energy NIR laser pulse at 1064 nm is directed onto the probe to vaporize and ionize particle components. Delayed pulse extraction is then used to sample the ions into a reflectron time of flight mass spectrometer for chemical analysis. The soft ionization afforded by the NIR photons results in minimal fragmentation (loss of a hydrogen atom) producing intact pseudo-molecular anions at [M-H]−. The limit of detection measured for pure oleic acid particles (geometric mean diameter and standard deviation of 180 nm and 1.3, respectively) was 140 fg (or 1.7 ng m−3 per minute sampling time). As an example of the utility of NIR-LDI-AMS to measurements of atmospheric importance, the method was applied to laboratory chamber measurements of the secondary organic aerosol formation from ozonolysis of α-pinene. High quality mass spectra were recorded with a 2-min time resolution for total aerosol mass loadings ranging from 1.5 to 8.7 μg m−3. These results demonstrate the potential of NIR-LDI-AMS to allow for more accurate measurements of the organic fraction of atmospheric particulate at realistic mass loadings. Measurements at ambient-levels of SOA mass loading are important to improve parameterizations of chamber-based SOA formation for modeling regional and global SOA fluxes and to aid in remediating the discrepancy between modeled and observed atmospheric total SOA production rates and concentrations.

Near-Infrared Laser Desorption/Ionization Aerosol Mass Spectrometry for Investigating Primary and Secondary Organic Aerosols under Low Loading Conditions

A new method, near-infrared laser desorption/ionization aerosol mass spectrometry (NIR-LDI-AMS), is described for the real time analysis of organic aerosols at atmospherically relevant mass loadings. Use of a single NIR laser pulse to vaporize and ionize particle components deposited on an aluminum probe results in minimal fragmentation to produce exclusively intact pseudomolecular anions at [M-H](-). Limits of detection (total particulate mass sampled) for oxidized compounds of relevance to atmospheric primary and secondary organic aerosol range from 89 fg for pinic acid to 8.8 pg for cholesterol. NIR-LDI-AMS was used in conjunction with the University of Vermont Environmental Chamber to study secondary organic aerosol (SOA) formation from ozonolysis of limonene at total aerosol mass loadings ranging from 3.2 to 25.0 μg m(-3) and with a time resolution of several minutes. NIR-LDI-AMS permitted direct delineation between gas-phase, homogeneous SOA formation and subsequent heterogeneous aerosol processing by ozone.

Total and methyl mercury transformations and mass loadings within a wastewater treatment plant and the impact of the effluent discharge to an alkaline hypereutrophic lake

Concerns over the fate and bioaccumulation of mercury (Hg) inputs to Onondaga Lake, a hypereutrophic lake in central New York, prompted an investigation into the concentrations and fluxes of Hg discharge from the Onondaga County Metropolitan Wastewater Treatment Plant (METRO WWTP). Discharge of methyl Hg (MeHg) is of concern because it is the form of Hg that readily bioaccumulates along the aquatic food chain. This study incorporated clean protocols for sampling and Hg analysis to evaluate: seasonal patterns in the concentrations of total Hg (THg) and MeHg in the WWTP unit processes; the production of MeHg within the unit processes of the WWTP; the overall fate of THg and MeHg within the WWTP; and the relative impact of the Hg discharged from the WWTP to Onondaga Lake. Concentrations of THg (range: 80–860 ng/L) and MeHg (0.7–17 ng/L) in raw sewage were highly variable, with higher concentrations observed in the summer months. The dynamics of THg though the WWTP were correlated with total suspended solids (TSS). As a result, the majority of the THg removal (55%) occurred during primary treatment. Overall, about 92% of the THg entering the plant was removed as sludge, with volatilization likely a minor component of the overall Hg budget. The transformation of MeHg through the plant differed from THg in that MeHg was not correlated with TSS, and displayed strong seasonal differences between winter (November to April) and summer (May–October) months. During the summer months, substantial net methylation occurred in the activated sludge secondary treatment, resulting in higher MeHg concentrations in secondary effluent. Net demethylation was the dominant mechanism during tertiary treatment, resulting in removal of substantial MeHg from the secondary effluent. The overall MeHg removal efficiency through the plant was about 70% with more efficient removal during summer months. Sediment trap collections made below the epilimnion of Onondaga Lake indicated average deposition rates of 12 μg/m 2-day for THg and 0.33 μg/m 2-day for MeHg. These deposition rates are more than an order of magnitude higher than the thermocline area normalized external loads from METRO effluent (0.85 μg/m 2-day for THg, 0.05 μg/m 2-day for MeHg). Our findings indicate that the impact of the discharge from METRO is relatively small, contributing about 10–15% of Hg to the total gross Hg input to the hypolimnion of the lake.

Volcanic ash and SO2 in the 2008 Kasatochi eruption: Retrievals comparison from different IR satellite sensors

The Kasatochi 2008 eruption was detected by several infrared satellite sensors including Moderate Resolution Imaging Spectroradiometer (MODIS), Advanced Very High Resolution Radiometer (AVHRR), and Atmospheric Infrared Sounder (AIRS). In this work a comparison between the volcanic cloud SO2 and ash retrievals derived from these instruments has been undertaken. The SO2 retrieval is carried out by using both the 7.3 and 8.7 μm absorption features while ash retrieval exploits the 10–12 μm atmospheric window. A radiative transfer scheme is also used to correct the volcanic ash effect on the 8.7 μm SO2 signature. As test cases, three near‐contemporary images for each sensor, collected during the first days of the eruption, have been analyzed. The results show that the volcanic SO2 and ash are simultaneously present and generally collocated. The MODIS and AVHRR total ash mass loadings are in good agreement and estimated to be about 0.5 Tg, while the AIRS retrievals are slightly lower and equal to about 0.3 Tg. The AIRS and MODIS 7.3 μm SO2 mass loadings are also in good agreement and vary between 0.3 and 1.2 Tg, while the MODIS ash corrected 8.7 μm SO2 masses vary between 0.4 and 2.7 Tg. The mass increase with time confirms the continuous SO2 injection in the atmosphere after the main explosive episodes. Moreover the difference between the 7.3 and 8.7 μm retrievals suggests a vertical stratification of the volcanic cloud. The results also confirm the importance of the ash correction; the corrected 8.7 μm SO2 total masses are less than 30–40% of the uncorrected values.

Concentrations and mass loadings of hormones, alkylphenols, and alkylphenol ethoxylates in healthcare facility wastewaters

Healthcare facility wastewaters are an anticipated source of known endocrine disrupting chemicals to the environment. In this study, the composition and magnitude of eight steroid hormones, octylphenol (OP), nonylphenol (NP), 16 nonylphenol ethoxylates (NPEOs), and 10 octylphenol ethoxylates (OPEOs) in wastewater from a(n) hospital, nursing facility, assisted living facility, and independent living facility are presented. Steroid hormone concentrations were variable for each sampling location, ranging from a non-detectable concentration of 17β-ethynylestradiol in all samples to 127 ng L −1 androstenedione in the hospital’s wastewater composite. OP and NP were not detected in any site’s samples. However, NPEOs were found at each sampling location with a maximum combined concentration of 260 μg L −1 for NPEOs with a chain length between 3 and 18 units in the assisted living facility composite sample. OPEOs were only found in the hospital and nursing facilities samples with a maximum combined OPEO concentration of 13 μg L −1 for OPEOs with a chain length between 2 and 12 units in hospital wastewater. The total mass loading of hormones to the municipal sewer system from each facility ranged from 2.5 mg d –1 at the assisted living facility to 138 mg d –1 at the hospital. The total mass loading of the alklyphenol ethoxylates (NPEO + OPEO) is considerably higher than the estimated hormone mass loadings, ranging from 1.8 g d –1 at the independent living facility to 54 g d –1 at the hospital facility.

Composite Electrodes for Electrochemical Supercapacitors

Manganese dioxide nanofibers with length ranged from 0.1 to 1 μm and a diameter of about 4–6 nm were prepared by a chemical precipitation method. Composite electrodes for electrochemical supercapacitors were fabricated by impregnation of the manganese dioxide nanofibers and multiwalled carbon nanotubes (MWCNT) into porous Ni plaque current collectors. Obtained composite electrodes, containing 85% of manganese dioxide and 15 mass% of MWCNT, as a conductive additive, with total mass loading of 7–15 mg cm−2, showed a capacitive behavior in 0.5-M Na2SO4 solutions. The decrease in stirring time during precipitation of the nanofibers resulted in reduced agglomeration and higher specific capacitance (SC). The highest SC of 185 F g−1 was obtained at a scan rate of 2 mV s−1 for mass loading of 7 mg cm−2. The SC decreased with increasing scan rate and increasing electrode mass.

Electrodes for Electrochemical Supercapacitors

Manganese dioxide nanoparticles were prepared by a chemical precipitation method. Composite electrodes for electrochemical supercapacitors (ES) were fabricated by impregnation of slurries of the manganese dioxide nanoparticles and carbon black into porous nickel foam current collectors. In the composite electrodes, carbon black nanoparticles formed a secondary conductivity network within the nickel foam cells. Obtained composite electrodes, containing manganese dioxide and 0–20 wt% carbon black with total mass loading of 55 mgcm−2, showed a capacitive behavior in the 0.1–0.5 M Na2SO4 solutions. The highest specific capacitance (SC) of 128 Fg−1 was obtained at a scan rate of 2 mVs−1 in the 0.5 M Na2SO4 solutions. The SC increased with increasing carbon black content in the composite materials and increasing Na2SO4 concentration in the solutions and decreased with increasing scan rate.

Results of a Self-Absorption Study on the Versapor 3000 47-mm Filters for Radioactive Particulate Air Stack Sampling

Since the mid-1980's the Pacific Northwest National Laboratory (PNNL) has used a value of 0.85 as a correction factor for the self absorption of activity for particulate radioactive air samples collected from building exhaust for environmental monitoring. More recently, an effort was made to evaluate the current particulate radioactive air sample filters (Versapor 3000, 47-mm diameter) used at PNNL for self absorption effects. There were two methods used to characterize the samples. Sixty samples were selected from the archive for acid digestion to compare the radioactivity measured by direct gas-flow proportional counting of filters to the results obtained after acid digestion of the filter and counting again by gas-flow proportional detection. Thirty different sample filters were selected for visible light microscopy to evaluate filter loading and particulate characteristics. Mass-loading effects were also considered. Large error is associated with the sample filter analysis comparison and subsequently with the estimation of the absorption factor resulting in an inadequate method to estimate losses from self-absorption in the sample filter. The mass loading on the sample filter as determined after digestion and drying was approximately 0.08 mg cm; however, this value may not represent the total filter mass loading given that there may be undetermined losses associated with the digestion process. While it is difficult to determine how much material is imbedded in the filter, observations from the microscopy analysis indicate that the vast majority of the particles remain on the top of the filter. In comparing the results obtained, the continued use of 0.85 as a conservative correction factor is recommended.

Sampling Strategies for Estimation of Parameters Related to Ground Water Quality

Multiple theoretical sampling designs are studied to determine whether sampling designs can be identified that will provide for characterization of ground water quality in rural regions of developing nations. Sampling design in this work includes assessing sampling frequency, analytical methods, length of sampling period, and requirements of sampling personnel. The results answer a set of questions regarding whether using innovative sampling designs can allow hydrogeologists to take advantage of a range of characterization technologies, sampling strategies, and available personnel to develop high-value, water-quality data sets. Monte Carlo studies are used to assess different sampling strategies in the estimation of three parameters related to a hypothetical chemical observed in a ground water well: mean concentration (MeanC), maximum concentration (MaxC), and total mass load (TML). Five different scenarios are simulated. These scenarios are then subsampled using multiple simulated sampling instruments, time periods (ranging from 1 to 10 years), and sampling frequencies (ranging from weekly to semiannually to parameter dependent). Results are analyzed via the statistics of the resulting estimates, including mean square error, bias, bias squared, and precision. Results suggest that developing a sampling strategy based on what may be considered lower quality instruments can represent a powerful field research approach for estimating select parameters when applied at high frequency. This result suggests the potential utility of using a combination of lower quality instrument and local populations to obtain high frequency data sets in regions where regular monitoring by technicians is not practical.