Real-Time Aerosol Density Determination Utilizing a Modified Scanning Mobility Particle Sizer—Aerosol Particle Mass Analyzer System

Real time secondary organic aerosol (SOA) density evolution for m-xylene photo-oxidation and α-pinene ozonolysis was obtained using an Aerosol Particle Mass Analyzer (APM)/Scanning Mobility Particle Spectrometer (SMPS) setup, which has been modified to achieve higher transmission of particles and improved sampling frequency. The aerosol density of SOA generated from α-pinene ozonolysis was found to be 1.24 ± 0.03 g/cm³ while the aerosol generated from m-xylene photo-oxidation was determined to be 1.35 ± 0.03 g/cm³. These results confirm the measurement approach from a combined SMPS and Aerodyne Aerosol Mass Spectrometer (AMS) system and are found to be within good agreement with the effective density measurements.     

Chemical Characteristics of Fine Particles (PM1) from Xi'an,China

Daily mass concentrations of water-soluble inorganic (WS-i) ions, organic carbon (OC), and elemental carbon (EC) were determined for fine particulate matter (PM₁, particles < 1.0 μm in diameter) collected at Xi'an, China. The annual mean PM₁ mass concentration was 127.3 ± 62.1 μg m^–3: WS-i ions accounted for ～38% of the PM₁ mass; carbonaceous aerosol was ～30%; and an unidentified fraction, probably mostly mineral dust, was ～32%. WS-i ions and carbonaceous aerosol were the dominant species in winter and autumn, whereas the unidentified fraction had stronger influences in spring and summer. Ion balance calculations indicate that PM₁ was more acidic than PM_2.5 from the same site. PM₁ mass, sulfate and nitrate concentrations followed the order winter > spring > autumn > summer, but OC and EC levels were higher in autumn than spring. Annual mean OC and EC concentrations were 21.0 ± 12.0 μg m^?3 and 5.1 ± 2.7 μg m^–3 with high OC/EC ratios, presumably reflecting emissions from coal combustion and biomass burning. Secondary organic carbon, estimated from the minimum OC/EC ratios, comprised 28.9% of the OC. Positive matrix factorization (PMF) analysis indicates that secondary aerosol and combustion emissions were the major sources for PM₁.     

Physical Characterization of Cigarette Smoke Aerosol Generated from a Walton Smoke Machine

Mainstream cigarette smoke generated using a Walton smoking machine and Kentucky 2R1 research cigarettes was studied. Results showed that puff volume and total particulate matter were consistent after the first puff, with average values of 35.6 cm³ and 3.37 mg, respectively. The particle size distribution, measured with a multijet cascade impactor, was not related to butt length or relative humidity (≤95%), but was strongly dependent on the aging time. Based on simple monodisperse coagulation, the mass median aerodynamic diameter was calculated to be 0.45 μm at a dilution ratio of 21.7. Using a technique based on the dimensional change of collected droplet particles at various viewing angles of a scanning electron microscope, the count median diameter was estimated to be 0.22 μm. These values were in good agreement with those reported by others. The results suggest that there is a dilution value critical to the rapid evaporation and final particle size of the cigarette smoke aerosol. Once reaching this value, further dilution has little effect on the final particle size. By using the derived mass concentration and size distribution, the particle density, number concentration, and coagulation coefficient of the cigarette smoke aerosol were estimated to be 1.12 g/cm³, 7.20 × 109 particles/cm³, and 6.64 × 10 ^?10 cm³/s respectively. Solid particles > 1 μm were found in the first few puffs. These were considered to consist of tobacco debris.     

Investigation of the specific attenuation cross-section of aerosols deposited on fiber filters with a polar photometer to determine black carbon

A polar photometer was used to investigate phase functions of glass fiber filters with varying aerosol particle loadings. Angle-resolved analysis revealed that the shape of the normalized phase function S_n(θ) in the transmitted hemisphere is independent of aerosol composition and determined exclusively by the fibrous filter matrix, while S_n(θ) in the reflected hemisphere depends on the scattering properties of the aerosol sample. Cross sensitivities of the specific attenuation cross section with respect to scattering components were examined with well-defined laboratory generated aerosol samples. The specific attenuation cross section at θ=165° (reflected hemisphere) was found considerably less dependent of the aerosol composition than any angular position in the transmitted hemisphere, and is therefore best suited for the determination of black carbon (BC). The angular position θ=165° was calibrated with an almost pure BC test aerosol. BC mass loadings of ambient aerosol samples (0.15–20 μg cm^-2) determined with this calibration function were in good agreement with values analyzed by coulometry.     

Effects of single-walled carbon nanotube filter on culturability and diversity of environmental bioaerosols

In this study, single-walled carbon nanotube (SWNT) filters were prepared using mixed cellulose ester (MCE) filters and carbon nanotubes with three levels of loading: 0.02, 0.16 and 0.64 mg/cm². Both MCE and SWNT filters were used to collect bacterial and fungal aerosols with a total volume of 200 L air sampled in indoor and outdoor environments. After sampling, the filters were directly placed on agar plates at 26 °C for culturing. The culturable aerosol counts were manually obtained both for MCE and SWNT filters, and the resulting bacterial colony forming units (CFUs) were washed off and subjected to the culturable bioaerosol diversity analysis using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). For fungal CFUs, microscopy method was used to study the diversity obtained using different filter types.The results showed that use of SWNT filters with medium and high CNT loadings resulted in significant reduction (up to 2 logs) of culturable bacterial and fungal aerosol counts compared to MCE filters in both environments. For low CNT loading (0.02 mg/cm²), very limited inactivation effects were observed for fungal aerosols, while more bacterial counts were obtained possibly due to increased sampling efficiency. PCR-DGGE analysis revealed that SWNT filters at high CNT loading (0.64 mg/cm²) resulted in lowest culturable bioaerosol diversity, especially pronounced for outdoor bacterial aerosols. For low and medium CNT loading, the culturable bacterial aerosol diversity remained similar. Fungal aerosol analysis showed that the use of SWNT filters with medium to high CNT loading also resulted in significant reduction of fungal species diversity. The results here demonstrated great promise of the SWNT hybrid filter in controlling biological aerosols, and suggested its potential to impact current air conditioning system.     

Counting Efficiencies for Alpha Particles Emitted from Wire Screens

Counting efficiencies for alpha particles emitted from the front and the back of 30-, 105-, 200-, and 400-mesh wire screens were measured for ultrafine radon daughter aerosols deposited at face velocities in the range 5.1 to 30.8 cm s^?1. Mean activity median diameters for the ultrafine ²¹⁸Po, ²¹⁴Pb, and ²¹⁴Bi particles were 0.70 ± 0.16, 1.1 ± 0.3, and 1.0 ± 0.2 nm (0.062, 0.033, and 0.038 cm² s^?1), respectively, as determined from graded wire screen array analysis of the test atmosphere. For wire screen collection efficiencies < 0.8, the “front-to-total” (FT) ratio, denned as the ratio of measured alpha activity from the front of the screen to the total alpha activity (front and back), was found to be insensitive to the screen and sampling parameters, with a mean value of 0.67 ± 0.02. With increasing collection efficiency, the FT ratio was found to increase, up to a maximum value of 0.86 ± 0.03 for collection efficiencies > 0.999. Alpha-particle losses within the screens (screen loss factors) were determined by comparison with counting efficiencies for radon daughters deposited onto membrane filters. For the four screen types studied, the mean screen loss factor at a face velocity of 21.2 cm s^?1 was 1.04 ± 0.01. A Monte Carlo simulation of alpha-particle losses within a simple woven wire screen showed that the FT ratios were sensitive to the functional form of the deposition of the radioactive aerosol around the wire cylinders of each screen. Screen loss factors derived from the Monte Carlo analysis were found to be insensitive to the deposition on the wire, but dependent upon the counting geometry, in particular the distance between the wire screen and the detector.     

Simultaneous transmission and absorption photometry of carbon-black absorption from drop-cast particle-laden filters

Simultaneous transmissivity and absorptivity measurements were carried out in the visible at a laser wavelength of 532?nm on drop-cast, carbon-black-laden filters under ambient (laboratory) conditions. The focus of this investigation was to establish the feasibility of this approach to estimate the mass absorption coefficient of the isolated particles and compare results to earlier work with the same carbon-black source. Transmissivity measurements were carried out with a laser probe beam positioned normal to the particle-laden filter surface. Absorptivity measurements were carried out using a laser-heating approach to record in time the sample temperature rise to steady-state and decay back to the ambient temperature. The sample temperature was recorded using a fine-wire thermocouple that was integrated into the transmission arrangement by placing the thermocouple flush with the filter back surface. The advantage of this approach is that the sample absorptivity can be determined directly (using laser heating) instead of resolving the difference between reflectivity (filter surface scattering) and transmissivity. The current approach also provides the filter optical characteristics, as well as an estimate of filter effects on the absorption coefficient due to particle absorption enhancement or shadowing. The approach may also be incorporated into other filter-based techniques, like the particle/soot absorption photometer, with the simple addition of a thermocouple to the commercial instrument. For this investigation, measurements were carried out with several blank uncoated quartz filters. A range of solution concentrations was prepared with a well-characterized carbon black in deionized water (i.e., a water-soluble carbonaceous material referred to as a surrogate black carbon or ‘carbon black’). The solution was then drop cast using a calibrated syringe onto blank filters to vary particle loading. After evaporation of the water, the measurements were repeated with the coated filters. The measurement repeatability (95% confidence level) was better than 0.3?K for temperature and 3?×?10^?5 mW for laser power. From the measurements with both the blank and coated filters, the absorption coefficient was determined for the isolated particles. The results were then compared with an earlier investigation by You et al. and Zangmeister and Radney, who used the same carbon-black material. The measurements were also compared with Lorenz–Mie computations for a polydispersion of spherical particles dispersed throughout a volume representative of the actual particles. The mass absorption coefficient for the polydispersion of carbon-black particles was estimated to be about 7.7?±?1.4?m² g^?1, which was consistent with the results expected for these carbon black particles.     

Scattering and absorption coefficients vs. chemical composition of fine atmospheric aerosol particles under regional conditions in Hungary

The light scattering and absorption coefficients of aerosol particles with a dry diameter below 1 μm were recorded in the country air of Hungary. Concentrations of different inorganic and organic ions were measured in parallel to estimate the nature of particles causing light scattering. The sample air was heated gently to maintain a relative humidity of 30% and coarse particles were removed by a multi-jet impactor. The aerosol light scattering coefficient was monitored with an integrating nephelometer, while absorption was measured on the basis of the rate of blackening of a filter. Results gained during two time periods, mostly in the winter months, are presented in this paper. Data show that the winter average light scattering coefficient is 93 Mm⁻¹, while the corresponding figure for light absorption is 8.9 Mm⁻¹. This results in a single-scatter albedo of 0.91. Comparison of the optical data with chemical information indicates that there is a good correlation between light scattering coefficient and sulfate concentration. The relationship is significant, in particular, in the winter half-year. Regression calculations among the measured parameters suggest for summer and winter half-year a sulfate mass scattering efficiency of 6 and 8 m² g⁻¹, respectively. By using a mass absorption efficiency of 10 m² g⁻¹, the average winter absorption coefficient corresponds to an elemental carbon concentration of 0.9 μg m⁻³.     

Collection efficiency of sintered ceramic filters made of submicron spheres

The performance of filters made of sintered submicron alumina particles was evaluated. The filter has a high collection efficiency and high pressure drop, requiring the development of a special measuring system for its evaluation. The system consists of a polydisperse NaCl particle generator, a differential mobility analyzer (DMA), an ejector to supply aerosols for testing filters with high pressure drop, and a mixing-type condensation nucleus counter (CNC) capable of obtaining a stable reading of very low concentration particles. Penetrations as low as 10⁻⁹ can be measured in the particle diameter range of 0.02-0.14 μm. Two filters made by sintering 0.60 and 0.84 μm alumina particles were evaluated. The experimental data collected served as the basis of theoretical development. Following the single fibre theory, the filter penetration is calculated by using a single sphere as the element. Both the diffusion and interception collection mechanisms were taken into account. The resulting equation gives a general trend of efficiency curves as a function of the parameters involved, e.g. the test aerosol size, packed particle size and filtration velocity. However, it is not sufficiently accurate for providing quantitative performance results.     

Design and characterization of a novel single-particle polar nephelometer

A new polar nephelometer (PN) has been developed to measure simultaneously the scattering angular distributions from 11.7° to 168.3° for individual particles in planes parallel and perpendicular to the polarization of the incident laser beam. Each detection plane had 21 silicon photodiode detectors to detect scattered light at a rate of 100 Hz. Laboratory experiments to validate the performance of the instrument were conducted using nearly mono-disperse spherical particles (polystyrene latex [PSL] and nigrosine) and nonspherical particles (sodium chloride [NaCl] and soot). The observed scattering angular distributions for individual PSL particles were in good agreement with the results of simulations based on Mie theory. Complex refractive index values for nigrosine particles were determined by comparing the observed scattering angular distributions with the results of simulations. Clear differences between the measured scattering angular distributions and the results of simulations based on Mie theory assuming spherical particles were observed for NaCl particles (mobility diameters of 500 and 700 nm) and propane soot particles (mobility diameters of 300, 500, and 700 nm). These results are reasonably explained by theoretical predictions. We also conducted initial observations of ambient particles in Nagoya city, Japan. Scattering angular distributions for particles with a mobility diameter of 500 nm and an average effective density of 1.4 or 0.3 g/cm³, which were selected with a combination of differential mobility analyzer and aerosol mass particle analyzer, were measured using the PN. As results, scattering angular distributions for nearly spherical inorganic and organic particles with an average effective density of around 1.4 g/cm³ were found to be distinguishable from nonspherical particles with an average effective density of around 0.3 g/cm³. This study has demonstrated that our PN has the potential to distinguish between spherical and nonspherical particles.

Copyright © 2016 American Association for Aerosol Research     

Absorption and Scattering Properties of Dust Clouds at 10.5-μm

Mass-density-normalized absorption and extinction coefficients for arid region soil-based dust were measured at a wavelength of 10.5 μm using photoacoustical techniques, short-path transmissometry, and aerosol dosimetry. An environmental chamber incorporating strong circulation, as well as the various aerosol sampling systems, was specifically designed for aerosol size distributions with particles as large as 40 μm in radius.

The mass extinction coefficient was found to be 0.22 m²/g, while the single scattering albedo, determined from the absorption and extinction coefficients, was 0.5. Calculations of these properties were based on two approaches: analyses of size distributions from photomicrographs of filter samples and analyses of the results obtained using a mixed-medium settling theory. In both cases, Mie theory was applied despite the clearly irregular particle forms. Agreement was close to the measured value for both approaches. The expected overestimation of the optical properties for the former model did not occur. Larger particles in this range are included because of their relevance to arid region dust clouds.     

Fourier Transform Infrared and Ion-Chromatographic Sulfate Analysis of Ambient Air Samples

Fourier transform infrared (FTIR) spectrometry has been evaluated as a method for determining the sulfate concentration of ambient aerosol particulate samples. Samples were collected on Teflon filters. The filters were analyzed for sulfate by both FTIR and ion chromatography (IC). There is good agreement between sulfate analysis by IC and analysis of the FTIR transmission spectra of the air filters during the first 5 1/2 days of the Carbonaceous Species Methods Intercomparison Study in which the ambient sulfate concentrations were above the 5.8 μg/cm² lower limit of detection of the FTIR technique. A method to improve the FTIR lower limit of detection is discussed. The difficulties incurred during background subtraction of the infrared spectra are described.     

Surface-collection efficiency of Nuclepore filters for nanoparticles

The flat surface of Nuclepore filters is suitable for observing collected particles with a scanning electron microscope (SEM). However, experimental data on surface-collection efficiency are limited because surface-collection efficiencies cannot be measured directly using aerosol measuring instruments. In this study, the surface-collection efficiencies of Nuclepore filters were determined by establishing the ratio of the number of particles deposited on the surface of the filter visually counted with an SEM to the number of inflow particles counted by a condensation particle counter, using monodispersed polystyrene latex particles (30–800 nm) and silver particles (15–30 nm). Because Nuclepore filters with smaller pore sizes would be expected to produce higher minimum surface-collection efficiency and a higher pressure-drop, 0.08 and 0.2 µm Nuclepore filters were chosen as the test filters in view of both collection efficiency and pressure drop. The results showed that the minimum surface-collection efficiencies of the 0.08 µm pores at face velocities of 1.9 and 8.4 cm·s^?1 were approximately 0.6 and 0.7, respectively, and those of the 0.2 µm pores at face velocities of 1.5 and 8.6 cm·s^?1 were approximately 0.8 and 0.6, respectively. Because the pressure drop of the 0.2 µm pore filter was lower than that of the 0.08 µm pore filter under the same flow-rate conditions, the 0.2 µm pore filter would be more suitable considering the pressure drop and collection efficiency. The obtained surface collection efficiencies were quantitatively inconsistent with theoretical surface-collection efficiencies calculated using conventional theoretical models developed to determine the collection efficiency of filters with larger pores.

© 2016 American Association for Aerosol Research     

Characterization of Combustion Aerosol Produced by a Mini-CAST and Treated in a Catalytic Stripper

We characterized the properties of combustion aerosol produced at different operating conditions of a mini-CAST burner that was treated in a Catalytic Stripper (CS) operating at 300°C. The goal was to establish a methodology for the production of soot particles resembling those emitted from internal combustion engines. Thermo-optical analysis of samples collected on Quartz filters revealed that the particles contained semi-volatile material that survived the CS. The amount of semi-volatile species strongly depended on the operating conditions ranging from less than 10% to as high as 30% of the particle mass. The mini-CAST operating conditions were also found to have a strong effect on the effective particle density (ρ_e ). The ρ_e , for example, ranged from as low as 0.3 to 1.05 g/cm³ for mondisperse 80 nm particles, although the mass-mobility exponent remained relatively constant (2.1–2.25). These differences are indicative of differences in the primary particle diameter, which was estimated to range between 8.5 and 34 nm depending on the operating conditions. The different types of particles produced were also found to exhibit different affinities for butanol but also different light absorption per mass of elemental carbon which can, therefore, lead to inconsistencies in aerosol instrumentation calibrations (e.g., condensation and optical particle counters, photoacoustic sensors). The work highlights the importance of establishing a detailed and well-defined method in using the mini-CAST-CS approach for instrument calibration in ways mimicking various engine combustion sources.

Copyright 2013 American Association for Aerosol Research     

Electrostatic Enhancement of the Collection Efficiency of Stainless Steel Fiber Filters

This study investigated the effect of using a stainless steel fibrous filter as the ground electrode of a point-to-plate electrostatic precipitator on particle penetration. The effect of the electrical field on particle penetration was investigated at 4 different filter face velocities (25, 50, 100, and 125 cm/s) for monodisperse PSL and silica particles (size range 0.05-1 m) as well as polydis perse ammonium sulfate, ammonium nitrate, and ultrafine indoor air particles. Particle penetration was greatly reduced by the application of the electrical field. By comparison, the performance of electrically active fibrous filters has been shown to rapidly degrade as particle loading exceeds 2-3 g/m². The effect of particle loading on particle penetration was also investigated at a filter face velocity of 50 cm/s. Particle penetration seemed to slightly decrease with particle loading and was independent of particle size. These results indicated that the accumulation of nonconductive particles up to 15 cm³/ m² does not create ''back corona,'' which would substantially decrease the collection efficiency of the grounded filter. In conclusion, our experiments suggest that using metal filters as the collector electrodes may be an attractive alternative design for electrostatic precipitators.     

A Study of Optical Properties of Soot Aggregates Composed of Poly-Disperse Monomers Using the Superposition T-Matrix Method

The diameters of soot monomers may not be constant in the single fractal aggregated soot particle. The optical properties of light absorbing soot particles aggregated with poly-disperse monomers were studied using the superposition T-matrix method. Soot aggregates were generated with different log-normal probability distribution functions (PDF) of soot monomer diameter, according to the same soot volumes and monomer numbers. The single scattering properties of soot particles were calculated at a wavelength of 550 nm, assuming a soot refractive index of 1.95 + 0.79i and a mass density of 1.8 g/cm³. The random-orientation averaging results indicated that the optical properties of soot aggregates were fairly varied for the different distributions of the monomer diameters. In these simulations, the extinction and absorption of soot aggregates were slightly (<10%) affected by the monomer poly-dispersity. The simulated mass absorption cross-sections (MAC) of fresh dry soot particles aggregated with poly-disperse monomers reached up to 6.62 ± 0.07 m²/g, which was closer to the measurement (7.5 ± 1.2 m²/g) than the assumption of volume-equivalent mono-disperse monomer (6.36 ± 0.06 m²/g). Moreover, the optical properties of soot coated with an organic shell were calculated, and the optical results showed that the absorption cross-sections of the internally mixed soot particles were also slightly (<8%) influenced by the monomer poly-dispersity. We found that the effect of the monomer poly-dispersity on the light scattering and the single scattering albedo may be considerably large (up to ?50% in extreme cases) for fresh dry soot aggregates. This effect on light scattering should be taken into account for those aggregates composed of monomers with widely distributed diameters.

Copyright 2015 American Association for Aerosol Research     

A Device for Generating Singly Charged Particles in the 0.1–1.0-μm Diameter Range

In this paper an aerosol charger that largely avoids the production of multiply charged particles in the 0.1–1.0 μm diameter range is described. The input aerosol is first passed through an electrostatic condenser to remove all charged particles and ions. The remaining neutral aerosol then flows into a 23-cm-long, 2.1-cm inner diameter cylindrical tube; the inner surface of this tube is uniformly coated with 0.09 μCi⁶³ Ni, a 0.067 MeV β-emitter with a half-life of 92 years. At typical airflow rates of 0.2–1.0 lpm, this low-activity source of ionizing radiation produces bipolar ion concentrations ranging from 1 × 10⁴ to 9 × 10⁴ ion/cm³, which is much lower than levels required to bring the aerosol to Boltzmann charge equilibrium. At a flow rate of 1.0 lpm, particles smaller than about 1.0 μm typically interact with no more than one ion en route through the charger. Therefore, particles at the charger exit are mostly either neutral or singly charged. Charge distributions of initially-neutral mono-disperse polystyrene latex particles were measured at the exit from the charger for particle diameters ranging in size from 0.09 to 1.09 μm. It was found that, at an airflow rate of 1.0 lpm and particle size 1.09 μm, the ratios of singly, doubly, and triply charged to total positively charged concentrations were 0.75, 0.19, and 0.06 respectively; particles with more than three charges were not detected. In contrast, the analogous charge ratio at Boltzmann equilibrium is 0.28 (+ 1), 0.24 (+ 2), 0.19 (+ 3), 0.13 (+ 4), 0.08 (+ 5), 0.05 (+ 6), and 0.7 (+ 02).     

First measurements of the number size distribution of 1–2 nm aerosol particles released from manufacturing processes in a cleanroom environment

This study was conducted to observe a potential formation and/or release of aerosol particles related to manufacturing processes inside a cleanroom. We introduce a novel technique to monitor airborne sub 2 nm particles in the cleanroom and present results from a measurement campaign during which the total particle number concentration (>1 nm and >7 nm) and the size resolved concentration in the 1 to 2 nm size range were measured. Measurements were carried out in locations where atomic layer deposition (ALD), sputtering, and lithography processes were conducted, with a wide variety of starting materials. During our campaign in the clean room, we observed several time periods when the particle number concentration was 10⁵ cm^?3 in the sub 2 nm size range and 10⁴ cm^?3 in the size class larger than 7 nm in one of the sampling locations. The highest concentrations were related to the maintenance processes of the manufacturing machines, which were conducted regularly in that specific location. Our measurements show that around 500 cm^?3 sub 2 nm particles or clusters were in practice always present in this specific cleanroom, while the concentration of particles larger than 2 nm was less than 2 cm^?3. During active processes, the concentrations of sub 2 nm particles could rise to over 10⁵ cm^?3 due to an active new particle formation. The new particle formation was most likely induced by a combination of the supersaturated vapors, released from the machines, and the very low existing condensation sink, leading to pretty high formation rates J_{1.4 nm} = (9 ± 4) cm^?3 s^?1 and growth rates of particles (GR_{1.1–1.3 nm} = (6 ± 3) nm/h and GR_{1.3–1.8 nm} = (14 ± 3) nm/h).

Copyright © 2017 American Association for Aerosol Research     

Intermediate Air Filters for General Ventilation Applications: An Experimental Evaluation of Various Filtration Efficiency Expressions

Neither the European standard nor the US standard for classification of intermediate class filters comprises testing of filter performance with respect to ultrafine particles (UFPs) or particles of the most penetrating size (MPPS). This could turn out to be a major lack in classification standards since UFPs have been pointed out as a serious health hazard. In this study, fractional efficiencies of eight new full-scale bag filters and twenty-three new filter medium samples were determined. The influence of air velocity and aerosol type was investigated, and correlations between efficiencies for UFPs (EF_UFPs), MPPS-sized particles (EF_MPPS) and 0.4 μm-sized particles (EF_0.4μm) were established. The tested bag filters were challenged by four aerosol types: a neutralized atomized oil aerosol, the same oil aerosol but non-neutralized, a non-neutralized thermally generated oil smoke, and a “natural” indoor aerosol. The tests were carried out at different air velocities through the filter medium, ranging between 0.08 m/s and 0.22 m/s. The relationships that were observed between EF_UFPs, EF_MPPS, and EF_0.4μm appeared to be linear within the observed filtration efficiency ranges. These relationships were similar regardless of the test aerosol type used, but somewhat different for glass fiber filters than for charged synthetic filters. Generally, EF_MPPS was 10–20% lower than EF_0.4μm. The influence of air velocity variations on the size resolved efficiency was determined. The glass fiber filters showed practically the same fractional efficiencies regardless of whether the test aerosol was neutralized or not. However, the charged synthetic filters showed substantially lower efficiencies when tested with the non-neutralized aerosol compared to the case when the aerosol was neutralized.

Copyright 2013 American Association for Aerosol Research     

Quantitative Photoelectron Spectroscopy (ESCA) of Sulfate Aerosol on Filtration Media

Photoelectron spectroscopy (ESCA) was applied to sub-micron sodium sulfate particles deposited on different filter surfaces. Only flat membrane filters were found to be suitable for aerosol analysis by ESCA. A linear dependence of ESCA signal on aerosol mass was observed for different polydisperse mass loadings on Nuclepore filters. We have also performed a systematic study of the relation between ESCA signal and particle diameter (30–220 nm). Lower detection limits range between 25 and 100 ng SO² ₄ per 0.25-cm² analyzed filter area, depending on particle radius and/or size distribution. We discuss future applications of ESCA in aerosol analysis.