Teflon Membrane Filters Research Articles

Characterization of The Permeation Properties of Membrane Filters and Sorption Properties of Sorbents Used for Polar Organic Chemical Integrative Samplers.

Polar organic chemical integrative samplers (POCIS) are promising devices for measuring the time-weighted average concentrations of hydrophilic compounds in aquatic environments. However, the mechanisms underlying compound uptake by POCIS remain unclear. We investigated the permeation kinetics of polyethersulfone and polytetrafluoroethylene membrane filters, and the sorption kinetics of Oasis HLB (Waters), Envi-Carb (Supelco), and Oasis WAX (Waters) sorbents. The log octanol-water partition coefficient (KOW) values of the 19 targeted compounds ranged from -0.55 to 6.0. The overall mass-transfer coefficients were negatively correlated with KOW, indicating that interactions between hydrophobic compounds and the membrane inhibit permeation. The sorption rate coefficient showed no correlation with KOW and depended on the type of sorbent used. These results imply that the uptake of highly hydrophilic compounds by POCIS is determined by both the membrane and the sorbent kinetics; however, membrane kinetics dominate the uptake of hydrophobic compounds. Environ Toxicol Chem 2024;43:2115-2121. © 2024 SETAC.

Construction of a convenient microbial-growth observation system based on microscopic image analysis applicable to the evaluation of preservative effects

The pour-plate method, a conventional approach to the evaluation of food microbial contamination, is costly and time-consuming. We have developed a novel and efficient system to evaluate microbial growth on the surfaces of foods using a membrane filter and microscope followed by image analysis. While Wickerhamomyces anomalus cells directly inoculated onto loin ham were undetectable because of the complex surface structure of the food, the placement of a hydrophilic polytetrafluoroethylene membrane filter on the loin ham enabled us to clearly observe the yeast cells on the filter by microscopy without affecting their growth. Under microscopic observation, cells on the membrane filter as well as those on the agar plate were always observed with surrounding annular dark regions, which were separated from the background by clear boundaries. We defined the areas inside the boundaries, including the cells and the annular dark regions, as the “bounded areas”. In image analysis, the numbers of pixels in the bounded areas increased exponentially in parallel with the viable cell count (CFU/g), suggesting that the pixel numbers were proportional to the viable cell numbers. We applied this system to investigate the adverse effects of sorbic acid preparation (SAP), a common food preservative, on yeast growth. The yeast was incubated on filter-overlaid agar medium in the presence or absence of SAP, resulting in a dose-dependent reduction in the specific pixel increase rate (k [/h]) determined by image analysis as well as in the specific growth rate (μ [/h]) estimated by the agar-plate-based conventional method. Regression analysis revealed a strong correlation between the k and μ values (R2, 0.985) normalized to the corresponding values without SAP. Our system could be applied to estimate the growth rate of microbes on foods and to examine the effects of environmental factors on microbial growth by using the k value as an index. Furthermore, this system would contribute to enhancing food safety, extending shelf life, and solving the important global problem of food loss.

Quantifying functional group compositions of household fuel-burning emissions

Abstract. Globally, billions of people burn fuels indoors for cooking and heating, which contributes to millions of chronic illnesses and premature deaths annually. Additionally, residential burning contributes significantly to black carbon emissions, which have the highest global warming impacts after carbon dioxide and methane. In this study, we use Fourier transform infrared spectroscopy (FTIR) to analyze fine-particulate emissions collected on Teflon membrane filters from 15 cookstove types and 5 fuel types. Emissions from three fuel types (charcoal, kerosene, and red oak wood) were found to have enough FTIR spectral response for functional group (FG) analysis. We present distinct spectral profiles for particulate emissions of these three fuel types. We highlight the influential FGs constituting organic carbon (OC) using a multivariate statistical method and show that OC estimates by collocated FTIR and thermal–optical transmittance (TOT) are highly correlated, with a coefficient determination of 82.5 %. As FTIR analysis is fast and non-destructive and provides complementary FG information, the analysis method demonstrated herein can substantially reduce the need for thermal–optical measurements for source emissions.

Assessment of the Pathogenic Potential of Microorganisms in Atmospheric Aerosols of Novosibirsk and Its Suburbs

Introduction: The atmosphere of Novosibirsk is characterized by increased levels of suspended particles, a significant part of which are bioaerosols. The latter include bacteria and fungi that can induce infectious diseases, allergies, and other negative responses in the population. Yet, the microbiota of ambient air of Novosibirsk and the region is poorly studied. Objective: To determine the concentration and composition of microorganisms in atmospheric aerosols of Novosibirsk and the region isolated in spring/summer 2023 and to test the microbial isolates for pathogenicity. Materials and methods: To isolate microorganisms from ambient aerosols, air was filtered applying Sartorius reinforced Teflon membrane filters and Hopar compressors. Their desorption from the filters was carried out by shaking in a physiological solution on a rocker and vortex followed by sowing the resulting suspensions onto nutrient media. We determined pathogenic signs by the presence of aggression enzymes and sensitivity of microbial isolates to antibiotics by the disk diffusion method. Sequencing of the 16S rRNA gene was performed by Sanger method; full genome sequencing was performed using the NextSeq 550 system. Results: During the study of the microbiota of atmospheric aerosols in Novosibirsk and the region in spring/summer 2023, fungi, spore-forming and non-spore-forming bacteria, both saprotrophic and pathogenic, were isolated with concentrations in the aerosol ranging from 100 to 8×103 CFU/m3, including multiple drug resistant ones. Fungi were generally represented by opportunistic and allergenic species of the genera Aspergillus, Alternaria, Cladosporium, Aureobasidium, and Penicillium, while bacteria – by a large variety of spore-forming and non-spore-forming bacterial species. Based on the results of analyzing phenotypic traits and the 16S rRNA gene sequencing, 119 bacterial isolates were identified. Full genome sequencing analysis and pathogenicity testing by secretion of catalase, hemolysins, lecithinase, lipase, plasma coagulase, alkaline phosphatase, gelatinase were performed for 49 of them along with testing for antibiotic resistance. We identified twenty-nine strains belonging to B. safensis, B. cereus, P. megaterium, B. mycoides, P. agglomerans, S. equorum, A. lwoffii, and a number of others with 5 to 7 positive reactions out of 9 in pathogenicity testing, capable of causing infectious diseases. Eleven strains showed resistance to 4 to 7 antibiotics, enabling their classification as multidrug-resistant. Conclusions: Detection of fungi and bacteria, which are among the most dangerous pathogens with multiple antimicrobial resistance, prove the necessity of constant control of the composition of bioaerosols in the urban environment.

The role of SVOCs in the initial film formation and soiling of unvarnished paintings

In recent years increased research efforts and environmental improvements have been directed towards the preventive conservation of the monumental, unvarnished oil paintings on canvas (1909–1916) by Edvard Munch (1863–1944) housed in the University of Oslo Aula. Surface soiling of the paintings has been a documented issue since their display, and the modern-day effect of air-borne particulates and gases on the painting surfaces remains hitherto undocumented. For the first time in the Aula, this study has measured the in-situ time-dependent mass deposit of air pollution onto vertical surfaces over the period of one year (2021–2022). Concomitant measurements of the concentrations of ozone (O3) and nitrogen dioxide (NO2) were also taken, to complement periodic data from 2020. The mass deposit was measured through incremental weight changes of Teflon membrane filters, and quartz filters for analysis of elemental/organic carbon (EC/OC), whilst the gaseous pollutants were measured using passive gas samplers. Indoor-to-outdoor ratios (I/O) for O3 were noted to be higher than those suggested by earlier data, whereas NO2 I/O ratios were found to be lower, indicating a stronger oxidising atmosphere in the Aula. Just over half of the deposited mass on the quartz filters was found to be OC, with no EC detected. Surprisingly, an overall decrease in the mass deposit from three to twelve months was measured on the Teflon membrane filters. It was hypothesised, based on models reported in the literature, that the source of the OC on the filters was mainly gaseous, semi-volatile organic compounds (SVOCs), which were present in an adsorption/desorption equilibrium that was dependent on possible SVOC emission episodes, relative humidity levels, gaseous oxidative reactions and the particulate matter deposit. A simple mathematical model is proposed to rationalise the observed mass deposits on the filters, together with a discussion of uncertainties affecting the measurements. The hypothesis preliminarily indicates the possible and previously unconsidered role of SVOCs on the initial film formation of soiling layers on the Aula paintings, and could bear implications for their monitoring in the preventive care of unvarnished oil paintings on canvas.

Evaluation of the ammonia emission sensitivity of secondary inorganic aerosol concentrations measured by the national reference method

A national reference method for fine particulate matter mass measurement usually specifies Teflon-membrane filter for the collection of ambient particles. Ammonium nitrate, one of the major components of fine particulate matter, is semi-volatile and susceptible to evaporation loss during and after field sampling by Teflon-membrane filter. The goal of this study is to evaluate the ammonia emission sensitivity of secondary inorganic aerosol (SIA) concentrations measured by the national reference method. The evaporation loss of particulate ammonium nitrate during and after field sampling was included in the analysis to cover a wide range of emission scenarios and meteorological conditions. The global to mesoscale air quality forecast and analysis system was used to predict the PM2.5 concentrations and chemical compositions. The predicted relative humidity and temperature were used to calculate the amount of ammonium nitrate evaporation loss from the thermodynamic equilibrium model. Except for the cool months, the particulate ammonium nitrate evaporation loss significantly decreases the ammonium nitrate contents in the SIA and subsequently degraded the effectiveness of ammonia emission control over the SIA. The SIA concentration decrease achieved by a 30% reduction of ammonia emission is lessened by 27–33% in the spring, 49–79% in the summer, 21–41% in the fall when the ammonium nitrate evaporation loss is included. We also proposed the normalized ammonia emission sensitivity of ammonium nitrate concentrations (γ(NH4NO3)) as a measure of the effectiveness of ammonia control and derived a mathematical relationship between γ(NH4NO3) and ammonia reduction rates in ammonia-rich conditions.

Passive permeation sampling of atmospheric HNO3

Passive samplers based on molecular diffusion are used to measure many organic and inorganic gaseous species in the atmosphere. In this study, the permeation resistance of two types of polytetrafluoroethylene membrane filters (TA300 and PF100, the same manufacturer but different membrane thicknesses) was evaluated and 0.2% NaCl-impregnated and polyamide filters (Nylasorb and Magna, different manufacturers) were compared as adsorbents for nitric acid (HNO3). As a reference, an annular denuder coated with NaCl was used for measuring HNO3 concentration. Based on the observed data and effective sampling area of the passive sampler, the sampling velocity (SV) was estimated and compared with reported values from other studies. The NaCl-impregnated filter had a slightly higher SV than the nylon (polyamide) filters. The SV for the thinner permeation filter, with a larger porosity (TA300) was much higher than the less porous filter (PF100). According to these results, the SV for a HNO3 passive sampler can be adjusted by selecting appropriate permeation filters according to the potential concentration at the sampling site and the maintenance schedule of the sampler.

Electrospun Cellulosic Membranes toward Efficient Chiral Resolutions via Enantioselective Permeation.

Cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC), known as one of the most versatile chiral selectors packed in columns for chiral chromatography, is electrospun for the first time. The electrospun nanofibers with a mean diameter of 329 nm form a self-standing nonwoven textile with a specific surface area of 5.6 m2/g. The textile is sandwiched between commercially available polytetrafluoroethylene membrane filters as a support material to fabricate a CDMPC membrane system for the chiral resolution of a racemic mixture, (R,S)-1-(1-naphthyl)ethanol. A vacuum filtration of the racemic mixture through the membrane system using a mixed solvent of n-hexane/2-propanol = 9/1 (v/v) enriches the S-enantiomer in the filtrate due to an enantioselective sorption of the R-enantiomer. The sorption capacity can be regenerated repeatedly via extractions of the adsorbed enantiomers from the membrane system after the filtrations. By repeating the vacuum filtration-extraction process for 15 cycles, the enantiomeric excess (e.e.) of the S-isomer in the filtrate increases up to 32.9%.

Review of Respirable Coal Mine Dust Characterization for Mass Concentration, Size Distribution and Chemical Composition

Respirable coal mine dust (RCMD) exposure is associated with black lung and silicosis diseases in underground miners. Although only RCMD mass and silica concentrations are regulated, it is possible that particle size, surface area, and other chemical constituents also contribute to its adverse health effects. This review summarizes measurement technologies for RCMD mass concentrations, morphology, size distributions, and chemical compositions, with examples from published efforts where these methods have been applied. Some state-of-the-art technologies presented in this paper have not been certified as intrinsically safe, and caution should be exerted for their use in explosive environments. RCMD mass concentrations are most often obtained by filter sampling followed by gravimetric analysis, but recent requirements for real-time monitoring by continuous personal dust monitors (CPDM) enable quicker exposure risk assessments. Emerging low-cost photometers provide an opportunity for a wider deployment of real-time exposure assessment. Particle size distributions can be determined by microscopy, cascade impactors, aerodynamic spectrometers, optical particle counters, and electrical mobility analyzers, each with unique advantages and limitations. Different filter media are required to collect integrated samples over working shifts for comprehensive chemical analysis. Teflon membrane filters are used for mass by gravimetry, elements by energy dispersive X-ray fluorescence, rare-earth elements by inductively coupled plasma-mass spectrometry and mineralogy by X-ray diffraction. Quartz fiber filters are analyzed for organic, elemental, and brown carbon by thermal/optical methods and non-polar organics by thermal desorption-gas chromatography-mass spectrometry. Polycarbonate-membrane filters are analyzed for morphology and elements by scanning electron microscopy (SEM) with energy dispersive X-ray, and quartz content by Fourier-transform infrared spectroscopy and Raman spectroscopy.

Improving filtration and pulse-jet cleaning performance of metal web filter media by coating with polytetrafluoroethylene microporous membrane

The metal web filter media has been widely used to purify high-temperature exhaust gas because of its good durability and reliability. Although it has fine high-temperature resistance, its filtration efficiency for fine particles is relatively low. In this study, we developed a new type of composite filter of metal web coated with polytetrafluoroethylene (PTFE) membrane, which combined the high-temperature resistance of the metal web filter and the excellent filtration performance of the membrane-coated filter media. The performance parameters of the composite filter, including pressure drop, filtration efficiency, regeneration efficiency, adhesive force, and high-temperature resistance, were investigated experimentally, and compared with those of the metal web filter and polyester fiber coated with PTFE membrane filter. Although the composite filter yielded a higher pressure drop, it exhibited a high particle collection efficiency. At a face velocity of 10.23cm/s, the filtration efficiency of the composite filter was 99.32 %. This was 1.23 and 0.10 % higher than that of the metal web filter and polyester coated with PTFE membrane filter, respectively. In addition, the composite filter has the characteristics of small cake/fabric adhesion force, low residual pressure drop, high regeneration efficiency, and long cleaning interval. The average cleaning interval and residual pressure drop of the composite filter were 421s and 425.0Pa, respectively, whereas those of the metal web filter were 291s and 658.5Pa, respectively; those of the polyester coated with PTFE membrane filter were 415s and 443.2Pa, respectively. Furthermore, the filtration test at high temperatures and thermogravimetric analysis demonstrated that the composite filter has an excellent thermal stability. At a temperature of 260°C, the average dust emission concentration of the polyester coated with PTFE membrane filter was 2.86 times larger than that of the composite filter (0.532mg/m3).

Aerosol light absorption from optical measurements of PTFE membrane filter samples: sensitivity analysis of optical depth measures

Abstract. Mass absorption cross section (MAC) measurements of atmospherically relevant aerosols are required to quantify their effect on Earth's radiative budget. Estimating aerosol light absorption from transmittance and/or reflectance measurements through filter deposits is an attractive option because of their ease of deployment in field settings, low cost, and the ability to revisit previously analyzed samples. These measurements suffer from artifacts that depend on a given filter measurement system and aerosol optics. Empirical correction algorithms are available for commercial instruments equipped with optically thick fiber filters, but optically thin filter media have not been characterized in detail. Here, we present empirical relationships between particle light absorption optical depth – measured using multiwavelength integrated photoacoustic spectrometers – and filter optical depth measurements for polytetrafluoroethylene (PTFE) membrane filter samples of carbonaceous aerosols generated from combustion of diverse biomass fuels and kerosene (surrogate for fossil fuel combustion). Through radiative transfer modeling, we assessed the suitability of three measures of filter-based optical depth for robustly describing particulate-phase light absorption over a range of single scattering albedo (SSA) values: (1) ODs – a measure of transmission of the fraction of incident radiation that is not backscattered by the filter system – which utilizes transmittance and reflectance of the sample side of the filter; (2) the commonly used ODc, which uses transmittance and reflectance of the clean side of the filter; and (3) ATN or the Beer–Lambert attenuation. Modeling results were also validated experimentally, with ODs showing the least variability around the mean in this multidimensional parameter space. We establish a simple, wavelength-independent formulation for calculating aerosol MAC and absorption coefficients from measurements of ODs. We find the ratio between in situ particulate absorption optical depth and ODs to be inversely proportional to aerosol SSA. Our findings underscore that ODs is a better optical depth measure than ODc for applying appropriate correction factors when estimating particle-phase light absorption from filter-based techniques.

A flow-through column electrolytic cell for supercritical fluid chromatography.

A novel flow-through column electrolytic cell was proposed as a detector to obtain current signals for supercritical fluid chromatography. The electrochemical cell consisted of two electrodes and its holder, and a working and a counter electrode were fabricated from 192 carbon strings, which were composed of 400 carbon fibers of 10μm in diameter filled into a heat-shrinkable tube. These electrodes were placed in the center of a holder made from polyether ether ketone blocks and they were separated by polytetrafluoroethylene membrane filters. To evaluate the sensitivity of this cell, a standard solution of ferrocene was injected into the supercritical fluid chromatography system connected to the electrolytic cell. The ferrocene was eluted through a silica gel column using a mixture of a mobile phase of supercritical CO2 and a modifier of methanol containing ammonium acetate. The current peak area of ferrocene correlated to the ferrocene concentration in the range of 10-400μmol/L (r=0.999). Moreover, the limit of detection on the column estimated from a signal-to-noise ratio of 3 was 9.8×10-13 mol.

Development of a novel immunoassay for herbal cannabis using a new fluorescent antibody probe, “Ultra Quenchbody”

We developed a novel immunoassay for herbal cannabis based on a new immunoassay principle that uses Ultra Quenchbody (“UQ-body”), a recombinant antibody Fab fragment fluorolabeled at the N-terminal regions. When the antigen binds to anti-Δ9-tetrahydrocannabinol (THC) UQ-body, the fluorescence intensity (FI) decreases. The analytical conditions of the immunoassay were optimized based on the FI reduction rate (FIRR). Following are the steps in the final analytical procedure: (1) 10mg of samples were extracted with 1ml of a 60:40 mixture of methanol and phosphate-buffered saline (PBS); (2) the extract was filtered through a centrifugal 0.2-μm polytetrafluoroethylene membrane filter; (3) the filtrate was diluted 100 times with extraction solvent; (4) 6-μl diluted solution was mixed with 19-μl PBS and 75-μl UQ-body solution; and (5) FIRR was measured under 275-mV excitation light. Herbal cannabis samples containing ≥4.0-mg/g THC gave FIRRs of ≥5.2%. FIRRs of negative samples (cigarette, tea, spice, and so-called “synthetic marijuana”) were ≤3.1%. When setting the FIRR threshold to 5.0%, cannabis samples containing ≥4.0-mg/g THC were correctly judged as positive without being affected by false positives caused by the negative samples. This detection limit was lower than total THC level (10–200mg/g) in most herbal cannabis samples seized in Japan. In seven of the 10 cannabis samples, the results of the UQ-body test were comparable with those of the Duquenois–Levine test. Thus, the UQ-body-based immunoassay is presumed to be an effective and objective drug screening method for herbal cannabis; however, to show the true usefulness, it is necessary to test a number of real case samples in the field situation.

Emissions and source profiles of PM2.5 for coal-fired boilers in the Shanghai megacity, China

A dilution system was deployed in parallel with a reference direct sampling system to measure the emission rates of PM2.5 and filterable particulate matters (FPM) and to establish the PM2.5 source profiles for coal-fired boilers in Shanghai, China. Three representative stacks were tested and twelve sets of samples were collected over six days with four runs per stack. The filters were weighed and analyzed for PM2.5 mass and chemical composition. The PM2.5 mass concentration for stationary sources equipped with high efficiency dust removal devices was approximately 8.7 mg/m3 on average, with a range of 4.8–13.1 mg/m3, while the PM2.5/FPM ratio was 0.72 on average with a range of 0.55–0.94. The chemical components of PM2.5 were normalized to PM2.5 mass measured from the Teflon-membrane filters after subtracting system blank. With these data the local coal-fired source primary PM2.5 profiles in Shanghai were established, showing characteristics of high abundances of SO42−, Ca2+, Al, Fe, S, organic carbon, and geological materials. The PM2.5 source profiles derived from this study showed significant differences from those reported in the literature, underlying the importance of establishing local source profiles for receptor-oriented source apportionment models.

Enhanced Point of Use Filtration for Cleaning without Small Particle Addition

Strict semiconductor cleaning demands for shrinking feature size and increased contamination sensitivity have led to projects that improve performance. The sources of contamination are generally the process chemicals themselves, where wafers are exposed to chemicals for etching or cleaning. Concerns over contamination are compounded in wet benches where chemical baths are re-circulated for periods up to 24 hours. Particle and metal impurities can arise from insufficiently pure chemicals/water, or liquid carry contaminants to the tools through plumbing components such as valves and pumps, and chemical containers/lines. Strict chemical, deionized water (DIW) and material specifications have benefited the industry. Currently, typical purity levels are below detection limits. That being said, point of use filtration offers enhanced reduction of contamination for critical cleans. In this paper we investigate particle adsorption on an immersed wafer surface in dilute HF and rinse applications. Particle addition for various immersion times in the tank can probe the contamination concentration in a solution. In this study, point of use filtration with tighter retention rating and cleaner devices is demonstrated to be critical for small particle control. 300mm wafers were processed by immersing a batch of up to 50 at a time in dilute HF and oxidizing agents for several minutes, rinsing and then drying. Inspection was conducted on a Surfscan SP3 system by KLA-Tencor. As shown below, the surface count of defects increases linearly with immersion time in HF for wafers processed normally. This demonstrates that particle contamination is present in the tank. Due to its acidic and etching nature (impact on particle zeta potential and silica concentration), HF processing is difficult in semiconductor processing. There is a need for enhanced particle retention filters with adequate flow rate to remove undesirable particles. The team evaluated tighter and cleaner Torrento® filters. Torrento® devices are polytetrafluoroethylene membrane filters that deliver contaminant protection performance for critical wet etch and cleaning technology. In a wafer manufacturing facility, recirculation filters were upgraded in a dilute HF tank. Tighter and cleaner Torrento® devices replaced the previous filters. Greater than one month of sampling was conducted, before and after the exchange. SP3 data for 32nm particles show that the average decreases >35%, and the standard deviation is reduced as well. Surface metals by VPD-ICPMS confirm no adverse effects. Separately, deionized water point of use purifier + filters were upgraded. Tighter retention Protego devices replaced the previously used purifiers. Protego® Plus ion-exchange purifier + filters are designed to reduce particles and metallic contamination during rinse. The Protego Plus technology is capable of processing DI water applications up to 80°C. Greater than one month of sampling was conducted, before and after the exchange. SP3 data for 26nm particles demonstrate that the average is reduced by >30%, and the standard deviation is lowered in turn. Surface metals by VPD-ICPMS show improvement (e.g. reduction in Na). Particle performance of acidic baths and DIW rinses has been shown to depend strongly on point of use filtration. Systematic studies of immersion time and large quantities of wafer production data are required to isolate the contribution and measure improvements. Figure 1

Mass reconstruction methods for PM2.5: a review.

Major components of suspended particulate matter (PM) are inorganic ions, organic matter (OM), elemental carbon (EC), geological minerals, salt, non-mineral elements, and water. Since oxygen (O) and hydrogen (H) are not directly measured in chemical speciation networks, more than ten weighting equations have been applied to account for their presence, thereby approximating gravimetric mass. Assumptions for these weights are not the same under all circumstances. OM is estimated from an organic carbon (OC) multiplier (f) that ranges from 1.4 to 1.8 in most studies, but f can be larger for highly polar compounds from biomass burning and secondary organic aerosols. The mineral content of fugitive dust is estimated from elemental markers, while the water-soluble content is accounted for as inorganic ions or salt. Part of the discrepancy between measured and reconstructed PM mass is due to the measurement process, including: (1) organic vapors adsorbed on quartz-fiber filters; (2) evaporation of volatile ammonium nitrate and OM between the weighed Teflon-membrane filter and the nylon-membrane and/or quartz-fiber filters on which ions and carbon are measured; and (3) liquid water retained on soluble constituents during filter weighing. The widely used IMPROVE equations were developed to characterize particle light extinction in U.S. national parks, and variants of this approach have been tested in a large variety of environments. Important factors for improving agreement between measured and reconstructed PM mass are the f multiplier for converting OC to OM and accounting for OC sampling artifacts.Electronic supplementary materialThe online version of this article (doi:10.1007/s11869-015-0338-3) contains supplementary material, which is available to authorized users.

Bacteriorhodopsin as a superior substitute for hydrazine in chemical reduction of single-layer graphene oxide sheets

Bacteriorhodopsin (bR) molecules were utilized as light-driven proton pumps for green as well as effective reduction of single-layer graphene oxide (GO) sheets. The bR molecules and graphene sheets were separated from each other in an aqueous environment by using a polytetrafluoroethylene membrane filter, in order to prevent their direct interactions (including attachment of the bR molecules onto the GO). Although reduction of GO using hydrazine or bR showed similar deoxygenation levels (based on X-ray photoelectron spectroscopy), the former resulted in formation of CN bonds which can substantially decrease the electrical conductivity of the reduced sheets. The electrical characteristics of the single-layer graphene sheets were studied by recording current–voltage curves of the sheets located between two Au electrodes on a SiO2 (300nm)/Si (100) substrate. The electrical conductivity of the bR-reduced graphene oxide (rGO) sheets was found about one order of magnitude better than that of hydrazine-rGO sheets. The excellent electrical conductivity of the bR-rGO sheets (with sheet resistance of ∼7.1×104Ω/sq) was assigned to the effective deoxygenation (without formation of any CN bonds) and better restoration of the graphitic structure of the GO sheets, using the protons pumped by the bR molecules.

Exposure to PM2.5 in modern office buildings through elemental characterization and oxidative potential

Fifty samples of indoor and outdoor PM2.5 were collected onto quartz fiber and Teflon membrane filters in five office buildings equipped with heating, ventilation and air-conditioning system for 8 h daily in order to coincide with the work shift of employees. Samples were analyzed for i) mass concentration; ii) elemental concentration; and iii) oxidative potential (OP) through antioxidant depletion. The PM2.5 mass concentration exceeded the annual mean guideline of 10 μg m−3 WHO in 50% of the samples. Indoor and outdoor PM2.5 mass concentrations correlated almost linearly. Proton-induced X-ray emission (PIXE) spectrometry was used for the monitoring of 21 elements. Quantitative determination was achieved in the case of Teflon filters only for Al, Si, S, Cl, K, Ca, Ti, Cr, Mn, Fe and Zn at ng m−3 concentration level. Quartz fiber filters were less adequate for the PIXE measurements due to their greater thickness and filamentary structure. Ca, Cr, Zn and Ti had generally higher concentration (mg g−1) indoors. Indoor/outdoor (I/O) OP values were higher than one in 14% and 57% of the samples in the case of ascorbate and reduced glutathione (GSH), respectively. Spatial and temporal variations of OP were observed across the office buildings. The I/O ratios for OP, Cr and Zn concentrations in the case of GSH were higher for three buildings. Significant relationship was observed between GSH oxidation and Cr and Zn concentrations. Thus, employees were exposed to a higher extent to reactive oxygen species in three buildings.

Ambient particulate matter air pollution in Mpererwe District, Kampala, Uganda: a pilot study.

Air quality in Kampala, the capital of Uganda, has deteriorated significantly in the past two decades. We made spot measurements in Mpererwe district for airborne particulate matter PM2.5 (fine particles) and coarse particles. PM was collected on Teflon-membrane filters and analyzed for mass, 51 elements, 3 anions, and 5 cations. Both fine and coarse particle concentrations were above 100 µg/m3 in all the samples collected. Markers for crustal/soil (e.g., Si and Al) were the most abundant in the PM2.5 fraction, followed by primary combustion products from biomass burning and incinerator emissions (e.g., K and Cl). Over 90% of the measured PM2.5 mass can be explained by crustal species (41% and 59%) and carbonaceous aerosol (33%–55%). Crustal elements dominated the coarse particles collected from Kampala. The results of this pilot study are indicative of unhealthy air and suggest that exposure to ambient air in Kampala may increase the burden of environmentally induced cardiovascular, metabolic, and respiratory diseases including infections. Greater awareness and more extensive research are required to confirm our findings, to identify personal exposure and pollution sources, and to develop air quality management plans and policies to protect public health.

Molecular tools to track bacteria responsible for fuel deterioration and microbiologically influenced corrosion

Investigating the susceptibility of various fuels to anaerobic biodegradation has become complicated with the recognition that the fuels themselves are not sterile. Bacterial DNA could be obtained when various fuels were filtered through a hydrophobic teflon (0.22 μm) membrane filter. Bacterial 16S rRNA genes from these preparations were PCR amplified, cloned, and the resulting libraries sequenced to identify the fuel-borne bacterial communities. The most common sequence, found in algal- and camelina-based biofuels as well as in ultra-low sulfur diesel (ULSD) and F76 diesel, was similar to that of a Tumebacillus. The next most common sequence was similar to Methylobacterium and was found in the biofuels and ULSD. Higher level phylogenetic groups included representatives of the Firmicutes (Bacillus, Lactobacillus and Streptococcus), several Actinobacteria, Deinococcus-Thermus, Chloroflexi, Cyanobacteria, Bacteroidetes, Alphaproteobacteria (Methylobacterium and Sphingomonadales), Betaproteobacteria (Oxalobacteraceae and Burkholderiales) and Deltaproteobacteria. All of the fuel-associated bacterial sequences, except those obtained from a few facultative microorganisms, were from aerobes and only remotely affiliated with sequences that resulted from anaerobic successional events evident when ULSD was incubated with a coastal seawater and sediment inoculum. Thus, both traditional and alternate fuel formulations harbor a characteristic microflora, but these microorganisms contributed little to the successional patterns that ultimately resulted in fuel decomposition, sulfide formation and metal biocorrosion. The findings illustrate the value of molecular approaches to track the fate of bacteria that might come in contact with fuels and potentially contribute to corrosion problems throughout the energy value chain.