Performance of wearable ionization air cleaners: Ozone emission and particle removal

Wearable ionization air cleaners are compact in size and marketed for personal respiratory protection by removing air pollutants from users' breathing zone. In this study, ozone emission and particle removal rates of four wearable ionization air cleaners (namely, AC1 through AC4) were evaluated inside a 0.46 m³ stainless steel chamber. Continuous measurements were conducted for ozone concentration, PM_2.5 concentration, and particle size distribution in the size range of 18.1–289 nm. Two of the four wearable air cleaners (i.e., AC1 and AC2) had detectable ozone emissions. The 10-h average ozone emission rates were quite different (i.e., 0.67 mg·h^?1 for AC1 and 3.40 × 10^?2 mg·h^?1 for AC2); however, the ozone emissions were negligible for AC3 and AC4. The number removal rates for particles within the measured size range were highly variable (i.e., 2.20 h^?1, 0.52 h^?1, 8.10 h^?1, and 27.9 h^?1 for AC1 through AC4, respectively). The corresponding mass removal rates of PM_2.5 were 1.85 h^?1, 0.48 h^?1_,1.52 h^?1, and 5.37 h^?1, respectively. Regulatory guidelines are needed to assure these devices can effectively remove particles without ozone emissions to protect public health.

Copyright © 2016 American Association for Aerosol Research     

Humidity,density, and inlet aspiration efficiency correction improve accuracy of a low-cost sensor during field calibration at a suburban site in the North-Western Indo-Gangetic plain (NW-IGP)

Abstract

Low-cost particulate matter (PM) sensors are now widely used by concerned citizens to monitor PM exposure despite poor validation under field conditions. Here, we report the field calibration of a modified version of the Laser Egg (LE), against Class III US EPA Federal Equivalent Method PM₁₀ and PM_2.5 β-attenuation analyzers. The calibration was performed at a site in the north-western Indo-Gangetic Plain from 27 April 2016 to 25 July 2016. At ambient PM mass loadings ranging from <1–838?µg m^?3 and <1–228?µg m^?3 for PM₁₀ and PM_2.5, respectively, measurements of PM₁₀, PM_2.5 from the LE were precise, with a Pearson correlation coefficient (r) >0.9 and a percentage coefficient of variance (CV) <12%. The original Mean Bias Error (MBE) of ～?90?µg m^?3 decreased to ?30.9?µg m^?3 (Sensor 1) and ?23.2?µg m^?3 (Sensor 2) during the summer period (27 April–15 June 2016) after correcting for particle density and aspiration losses. During the monsoon period (16 June–25 July 2016) the MBE of the PM_2.5 measurements decreased from 19.1?µg m^?3 to 8.7?µg m^?3 and from 28.3?µg m^?3 to 16.5?µg m^?3 for Sensor 1 and Sensor 2, respectively, after correcting for particle density and hygroscopic growth. The corrections reduced the overall MBE to <20?µg m^?3 for PM₁₀ and <3?µg m^?3 for PM_2.5, indicating that modified version of the LE could be used for ambient PM monitoring with appropriate correction and meteorological observations. However, users of the original product may underestimate their PM₁₀ exposure.

Copyright © 2020 American Association for Aerosol Research     

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.     

Physicochemical Characterization of Simulated Welding Fumes from a Spark Discharge System

This study introduces a spark discharge system (SDS) as a way to simulate welding fumes. The SDS was developed using welding rods as electrodes with an optional coagulation chamber. The size, morphology, composition, and concentration of the fume produced and the concentration of ozone (O₃) and nitrogen oxides (NO_X) were characterized. The number median diameter (NMD) and total number concentration (TNC) of fresh fume particles were ranged 10–23 nm and 3.1×10⁷ ? 6×10⁷ particles/cm³, respectively. For fresh fume particles, the total mass concentration (TMC) measured gravimetrically ranged 85–760 μg/m³. The size distribution was stable over a period of 12 h. The NMD and TNC of aged fume particles were ranged 81–154 nm and 1.5×10⁶?2.7×10⁶ particles/cm³, respectively. The composition of the aged fume particles was dominated by Fe and O with an estimated stoichiometry between that of Fe₂O₃ and Fe₃O₄. Concentrations of O₃ and NO_X were ranged 0.07–2.2 ppm and 1–20 ppm, respectively. These results indicate that the SDS is capable of producing stable fumes over a long-period that are similar to actual welding fumes. This system may be useful in toxicological studies and evaluation of instrumentation.

Copyright 2014 American Association for Aerosol Research     

Hong Kong vehicle emission changes from 2003 to 2015 in the Shing Mun Tunnel

ABSTRACT

This study characterized motor vehicle emission rates and compositions in Hong Kong's Shing Mun tunnel (SMT) during 2015 and compared them to similar measurements from the same tunnel in 2003. Average PM_2.5 concentrations in the SMT decreased by ～70% from 229.1 ± 22.1 µg/m³ in 2003 to 74.2 ± 2.1 µg/m³ in 2015. Both PM_2.5 and sulfur dioxide (SO₂) emission factors (EF_D) were reduced by ～80% and total non-methane (NMHC) hydrocarbons EF_D were reduced by 44%. These reductions are consistent with long-term trends of roadside ambient concentrations and emission inventory estimates, indicating the effectiveness of emission control measures. EF_D changes between 2003 and 2015 were not statistically significant for carbon monoxide (CO), ammonia (NH₃), and nitrogen oxides (NO_x). Tunnel nitrogen dioxide (NO₂) concentrations and NO₂/NO_x volume ratios increased, indicating an increased NO₂ fraction in the primary vehicle exhaust emissions. Elemental carbon (EC) and organic matter (OM) were the most abundant PM_2.5 constituents, with EC and OM, respectively, contributing to 51 and 31% of PM_2.5 in 2003, and 35 and 28% of PM_2.5 in 2015. Average EC and OM EF_D decreased by ～80% from 2003 to 2015. The sulfate EF_D decreased to a lesser degree (55%) and its contribution to PM_2.5 increased from 10% in 2003 to 18% in 2015, due to influences from ambient background sulfate concentrations. The contribution of geological materials to PM_2.5 increased from 2% in 2003 to 5% in 2015, signifying the importance of non-tailpipe emissions.

© 2018 American Association for Aerosol Research     

Analysis of Aerosolized Particulates of Feedyards Located in the Southern High Plains of Texas

The objective of this study was to quantify, size, and examine the composition of particulates found in ambient aerosolized dust of four large feedyards in the Southern High Plains. Ambient air samples (concentration of dust) were collected upwind (background) and downwind of the feedyards. Aerosolized particulate samples were collected using high volume sequential reference ambient air samplers, PM ₁₀ and PM _2.5 , laser strategic aerosol monitors, cyclone air samplers, and biological cascade impactors. Weather parameters were monitored at each feedyard. The overall (main effects and estimable interactions) statistical (P < 0.0001) general linear model statement (GLM) for PM ₁₀ data showed more concentration of dust (μg/m ³ of air) downwind than upwind and more concentration of dust in the summer than in the winter. PM _2.5 concentrations of dust were comparable for 3 of 4 feedyards upwind and downwind, and PM _2.5 concentrations of dust were lower in the winter than in the summer. GLM (P < 0.0001) data for cascade impactor (all aerobic bacteria, Enterococcus spp, and fungi) mean respirable and non-respirable colony forming units (CFU) were 676 ± 74 CFU/m ³ , and 880 ± 119 CFU/m ³ , respectively. The PM ₁₀ geometric mean size (±GSD) of particles were analyzed in aerosols of the feedyards (range 1.782 ± 1.7 μm to 2.02 ± 1.74μm) and PM _2.5 geometric mean size particles were determined (range 0.66 ± 1.76 μm to 0.71 ± 1.71 μm). Three of 4 feedyards were non-compliant for the Environmental Protection Agency (EPA) concentration standard (150 μg/m ³ /24 h) for PM ₁₀ particles. This may be significant because excess dust may have a negative impact on respiratory disease.     

Particulate matter characteristics,dynamics, and sources in an underground mine

Particulate matter (PM) from mining operations, engines, and ore processing may have adverse effects on health and well-being of workers and population living nearby. In this study, the characteristics of PM in an underground chrome mine were investigated in Kemi, Northern Finland. The concentrations and chemical composition of PM in size ranges from 2.5 nm to 10 µm were explored in order to identify sources, formation mechanisms, and post-emission processes of particles in the mine air. This was done by using several online instruments with high time-resolution and offline particulate sampling followed by elemental and ionic analyses. A majority of sub-micrometer particles (<1 µm in diameter, PM₁) originated from diesel engine emissions that were responsible for a rather stable composition of PM₁ in the mine air. Another sub-micrometer particle type originated from the combustion products of explosives (e.g., nitrate and ammonium). On average, PM₁ in the mine was composed of 62%, 30%, and 8% of organic matter, black carbon, and major inorganic species, respectively. Regarding the analyzed elements (e.g., Al, Si, Fe, Ca), many of them peaked at >1 µm indicating mineral dust origin. The average particle number concentration in the mine was (2.3 ± 1.4)*10⁴ #/cm³. The maximum of particle number size distribution was between 30 and 200 nm for most of the time but there was frequently a distinct mode <30 nm. The potential origin of nano-size particles remained as challenge for future studies.

Copyright © 2018 The Authors. Published with license by Taylor & Francis     

A Laboratory Comparison of Real-Time Measurement Methods for 10–100-nm Particle Size Distributions

We present information regarding the relative performance of five TSI particle sizing instruments when presented with several log-normally distributed particle populations that vary in terms of composition, concentration, and modal mean diameter (in the range of 10–100 nm) in a controlled laboratory environment. In experiments conducted with NaCl, NaNO₃, and organic aerosols, across a total particle concentration suite ranging from approximately 1 × 10⁴ cm^?3 to 1 × 10⁶ cm^?3, total number concentrations of sub-100-nm diameter particles from four SMPS systems and an FMPS all fall within ±50% of each other (and generally are within ±30%). However, larger discrepancies are evident in the particle size distribution, particularly for the NaCl particles, with an SMPS operated with a water-based CPC exhibiting large negative bias in modal peak concentrations relative to the isobutanol-based SMPS systems and the FMPS. Much closer agreement is found for NaNO₃ particles, although the SMPS systems tended to exhibit higher modal peak concentrations, and a slight shifting toward lower modal peak diameter than the FMPS.

Copyright 2014 American Association for Aerosol Research     

Characteristics and source identification study of ambient suspended particulates and ionic pollutants in an area abutting a highway

Ambient suspended particulates in an area abutting a highway were gathered using a Partisol Model 2300 Speciaton Sampler (RP2300). Major ionic species with different particle sizes and with possible sources close to the sampling site were evaluated using Principal Component Analysis (PCA). Observational results indicate that average PM_2.5 and PM₁₀ concentrations were 66.33 and 108.28 μg/m³, respectively. The average ratio of PM_2.5/PM₁₀ was 62% at this sampling site, whereas the average PM_2.5/PM₁₀ ratio in this study was less than those in urban (Seoul, Korea), suburban (Basel, Switzerland) and rural (Chaumont, Switzerland) settings. Average concentrations for ionic species of NO₃⁻, SO₄²⁻ and NH₄⁺ were 10.46, 12.63 and 7.87 μg/m³ in PM_2.5, respectively. Average concentrations for ionic species of NO₃⁻, SO₄²⁻ and NH₄⁺ were 17.28, 15.59 and 9.48 μg/m³ in PM₁₀, respectively. Principal component analysis identified soil, secondary aerosols and marine salt as possible major pollutant sources at this sampling site.     

PM1.0 and PM2.5 Characteristics in the Roadside Environment of Hong Kong

Daily mass concentrations of PM _1.0 (particles less than 1.0 μm in diameter), PM _2.5 (particles less than 2.5 μm in diameter), organic carbon (OC), and elemental carbon (EC) were measured from January through May 2004 at a heavily trafficked sampling site in Hong Kong (PU). The average concentrations for PM _1.0 and PM _2.5 were 35.9 ± 12.4 μ g cm ^{? 3} and 52.3 ± 18.3 μ g cm ^{? 3} . Carbonaceous aerosols were the dominant species in fine particles, accounting for ～ 45.7% of PM _1.0 and ～ 44.4% of PM _2.5 . During the study period, seven fine-particle episodes occurred, due to the influence of long-range transport of air masses from mainland China. PM _1.0 and PM _2.5 responded in similar ways; i.e., with elevated mass and OC concentrations in those episode days. During the sampling period, PM _1.0 OC and EC generally behaved similarly to the carbonaceous aerosols in PM _2.5 , regardless of seasonal variations and influence by regional pollutions. The low and relatively constant OC/EC ratios in PM _1.0 and PM _2.5 indicated that vehicular emissions were major sources of carbonaceous aerosols. PM _1.0 and PM _2.5 had the same dominant sources of vehicular emissions in winter, while in spring PM _2.5 was more influenced by PM _{1 ? 2.5} (particles 1–2.5 μ m in diameter) that did not form from vehicle exhausts. Therefore, PM _1.0 was a better indicator for vehicular emissions at the Roadside Station.     

The PAH and Nitro-PAH Concentration Profiles in Size-Segregated Urban Particulate Matter and Soil in Traffic-Related Sites in Catania,Italy

Polycyclic aromatic hydrocarbons (PAHs) and nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) were identified from both air particulate matter and soils. For air sampling, a six-stage cascade impactor was situated in an urban area (Catania, Italy) that is recognized for its high traffic volume. The soil samples were collected every 1.5 km from under the grass by the side of the median of a Catania road along its full length (8.2 km). HPLC in electrochemical-fluorescence detection mode was used for selective separation, identification and quantification of analytes in air and soil samples, providing both good selectivity and sensitivity. The seasonal trends, effects of urban traffic, and source profiles are discussed herein. Higher PM₁₀ concentrations were observed for summer (43 μg m^?3) in comparison to winter (24 μg m^?3). Conversely, the PAHs contained in PM₁₀ were higher in winter (0.48 ng m^?3 for fluoranthene) than in summer (0.14 ng m^?3 for fluoranthene). Analysis of the size-segregated urban particulate matter showed that the amount of PM_0.5 (stage 6) was always higher than the amount of other particles (stages 1–5). Furthermore, the PM_0.5 was always higher in summer (about 40%, m/m) than in winter (about 30%, m/m). Finally, the amounts of PAH and nitro-PAH in PM_0.5 (stage 6) were always higher, by a maximum of one order of magnitude, than that of other particles (stages 1–5). This result is crucial because ultrafine particles have a tendency to move into the blood through the alveolar epithelial barrier. Moreover, the air and soil pollution levels agree with those found in other cities with similar levels of pollution. Supplemental materials are available for this article. Go to the publisher's online edition of Polycyclic Aromatic Compounds to view the supplemental file.     

Characteristics of PM2.5 Episodes Revealed by Semi-Continuous Measurements at the Baltimore Supersite at Ponca St

Highly time-resolved measurements of PM_2.5, its major constituents, particle size distributions (9 nm to 20 μ m), CO, NO/NO₂, and O₃, and meteorological parameters were made from February through November 2002, at the Baltimore Supersite at Ponca St. using commercial and prototype semi-continuous instruments. The average PM_2.5 mass concentration during the study period was 16.9 μ g/m³ and a total of 29 PM_2.5 pollution episodes, each in which 24-h averaged PM_2.5 mass concentrations exceeded 30.0 μ g/m³ for one or more days, were observed. Herein, 6 of the worst episodes are discussed. During these events, PM_2.5 excursions were often largely due to elevations in the concentration of one or two of the major species. In addition, numerous short-term excursions were observed and were generally attributable to local sources. Those in OC, EC, nitrate, CO, and NO_x levels were often observed in the morning traffic hours, particularly before breakdown of nocturnal inversions. Moreover, fresh accumulation aerosols from local stationary combustion sources were observed on several occasions, as evidenced by elevations in elemental markers when winds were aligned with sources resulting in PM_2.5 increments of ～ 17 μ g/m³. Overall, the results described herein show that concentrations of PM_2.5 and its major constituents vary enormously on time scales ranging from < 1 hr to several days, thus imposing a more highly complex pattern of pollutant exposure than can be captured by 24-hr integrated methods, alone. The data suggest that control of a limited number of local sources might achieve compliance with daily and annual PM_2.5 standards.     

Performance of Low Cost Ceramic Microfiltration Membranes for the Treatment of Oil-in-water Emulsions

Using the uniaxial compaction method, ceramic disk type microfiltration membranes were fabricated using mixtures of clays to yield membranes M₁, M₂, and M₃. These were obtained with distinct compositions of raw materials at a sintering temperature of 900°C. Membrane characterization was conducted using thermogravimetric analysis (TGA), particle size distribution (PSD), X-ray diffraction (XRD), and scanning electron microscope analysis (SEM). Morphological characterization of these membranes includes the evaluation of average porosity, pore size, mechanical stability, chemical stability, and hydraulic permeance. With varying composition of the raw materials, it is observed that the average porosity and pore size of the membrane varied between 23–30% and 0.45 to 1.30 µm. For all membranes, the flexural strength varied within the range of 10-34 MPa. Chemical stability tests indicate that the membranes are stable in both acidic and basic media. The hydraulic permeance of M₁, M₂, and M₃ membranes is about 3.97 × 10^?6, 2.34 × 10^?6, and 0.37 × 10^?6 m³/m² s kPa, respectively. Further, the performance of these membranes was studied for the microfiltration of synthetic oily wastewater emulsions. Amongst all membranes, membrane, M₂ performance is satisfactory as it provides oil rejection of 96%, with high permeate flux of 0.65 × 10^?4 m³/m² s at a lower transmembrane pressure differential of 69 kPa for the oil concentration of 200 mg/L.     

Exposure to welding particles in automotive plants

This work presents a monitoring study designed to evaluate workers' exposure to particles in several body shops within automotive plants. Concentrations in the proximity of welding activities were measured by a Fast Mobility Particle Sizer, several Condensation Particle Counters, a Nanoparticle Surface Area Monitor and a laser photometer, as well as by several gravimetric samplers. Average concentrations were found to be 1×10⁵ part cm^?3, 3×10³ μm² cm^?3 and 0.4 mg m^?3 for number, surface area and PM₁ concentration, respectively (worst case). Very high concentrations, particularly for surface area, were observed in locations with a high density of manual resistance welding activities or close to oxyacetylene welding activities. Welding emission factors in the automotive plants were also evaluated and in the most critical body shop, the overall welding activities led to emission factors of 2.8×10¹⁵ part min^?1, 7.0×10⁶ μm² min^?1 and 7.9 g min^?1 for number, surface area and PM₁ concentrations, respectively. Finally, particle concentration characterization, along with air exchange ratio measurements in the body shop, showed that the indoor concentrations and, hence, worker particle exposure can be reduced through the use of local exhaust ventilation.     

The rates of emissions of fine particles from some Canadian coal-fired power plants

Particles emitted from three coal-fired power plants burning subbituminous coals from Alberta, Canada were examined for total particulate matter (PM) and size fractions PM_>10, PM₁₀, and PM_2.5. The sampling was carried out following EPA Method 201A, which requires a 6 inch port. Three tests were performed at each station. The rates of emitted particulates from the three power plants are 9.9-53.4 mg/m³ (dry), 30-90 kg/hr (dry), and 0.039-0.118 kg/MWh, respectively. The emission rates of the various particle sizes for these three power plants are 8.7-39.5 kg/hr of PM_>10, 10.7-40.8 kg/hr of PM₁₀, and 9.65-10.7 kg/hr of PM_2.5. The present results indicate that 29-44% of emitted particles are PM_>10. The total emissions of particulates from two power plants are below the Canadian Guideline for emission from a coal-fired power plant (0.095 kg/MWh), while the third power plant is slightly higher than the Guideline (0.118 kg/MWh).The malfunctioning of control technology may result in unrealistic and wide variation in the measured rates of emitted particles.     

Electrokinetic Properties of Acid-Activated Montmorillonite Dispersions

In this study, the influence of pH, electrolyte concentration, and type of ionic species on the electrokinetic properties (zeta potential and electrokinetic charge density) of the acid-activated montmorillonite mineral have been investigated using the microelectrophoresis method. The electrokinetic properties of acid-activated montmorillonite dispersions have been determined in aqueous solutions of mono-, di-, and trivalent salts and divalent heavy metal salts. Zeta potential experiments have been performed to determine the point of zero charge (pzc) and potential determining ions (pdi). The zeta potential values of the acid-activated montmorillonite particles were negative and did not vary significantly within the pH range studied. Acid-activated montmorillonite dispersions do not have point of zero charge (pzc). The valence of the electrolytes has a great influence on the electrokinetic behavior of the suspension. A gradual decrease in the zeta potential (from ?25 mV to ?5 mV) occurs with the monovalent electrolytes when concentration increased. Divalent and heavy metal electrolytes have less negative z-potentials due to the higher valence of ions. A sign reversal of z-potential has been observed at AlCl₃, FeCl₃, and CrCl₃ electrolytes (potential determining ions) and zeta potential values have had a positive sign at high electrolyte concentrations.

The electrokinetic charge density of acid-activated montmorillonite has shown similar trends for variation in mono- and divalent electrolyte solutions. Up to concentrations of ca. 10^?3 M, it has remained practically constant at approximately 0.5 × 10^?3 C m^?2 For higher concentrations of monovalent electrolytes more negative values (?16 × 10^?3 C m^?2) were observed. It has less negative values in divalent electrolyte concentrations according to monovalent electrolytes (?5 × 10^?3 C m^?2). For low concentrations of trivalent electrolytes, the electrokinetic charge density of montmorillonite particles is constant, but at certain concentrations it rapidly increased and changed its sign to positive.     

Effects of Tb doping on structural and electrical properties of 47(Ba0.7Ca0.3)TiO3–0.53Ba(Zr0.2Ti0.8)O3 thin films at various annealing temperature by pulsed laser deposition

The ceramic thin films of 47(Ba_0.7Ca_0.3)TiO₃–0.53Ba(Zr_0.2Ti_0.8)O₃ (BCZT) + x (x = 0.2, 0.3, 0.4 and 0.5) mol% Tb were grown on Pt(111)/Si substrates with various annealing temperature by pulsed laser deposition. The XRD spectra confirm that Tb element can enhance the (l10) and (111) orientations in ceramic films. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images show that Tb-doping can increase particle size effectively. The surface of Tb-doped film annealed at 800 ℃ is uniform and crack-free, and the average particle size and mean square roughness (RMS) are about 280 nm and 4.4 nm, respectively. Comparing with pure BCZT, the residual polarization (P_r) of 0.4 mol% Tb-doped film annealed at 800 ℃ increase from 3.6 to 9.8 μC/cm². Moreover, the leakage current density value of Tb doped films are one order of magnitude (5.33 × 10^?9?1.97 × 10^?8 A/cm² under 100 kV/cm) smaller than those of pure BCZT films (1.02 × 10^?7 A/cm²).     

Tailpipe emission characteristics of PM2.5 from selected on-road China III and China IV diesel vehicles

Eighteen China III and IV diesel vehicles, including light-duty diesel trucks (LDDTs), medium-duty diesel trucks (MDDTs), heavy-duty diesel trucks (HDDTs) and buses, were tested with real-world measurements using a portable emission measurement system (PEMS). The emission factors (EFs), chemical components and surface morphology of emitted particles from these vehicles were characterized. Measured features included organic carbon (OC), elemental carbon (EC), water soluble ions (WSIs) and trace elements of PM_2.5. The modelling system MOtor Vehicle Emission Simulator (MOVES) was also employed to estimate the PM_2.5 EFs from these vehicles. Carbonaceous content made up 35.8–110.8% of PM_2.5, the largest contribution of all the determined chemical components; WSIs and elements accounted for less than 10%. The average PM_2.5 EFs of MDDTs and HDDTs were 0.389 g·km^?1 and 0.115 g·km^?1, respectively, approximately one order of magnitude higher than that of LDDTs. The PM_2.5 EFs of China III buses were much lower than those of China III MDDTs and HDDTs, indicating that the inspection maintenance program (I/M) system was carried out effectively on public diesel vehicles. Moreover, the chemical composition of 9.2–56.2% of the PM_2.5 mass emitted from China IV diesel trucks could not be identified in the present study. It was possible this unidentified mass was particle bound water, but this hypothesis should be confirmed with further measurements. The SEM images of PM_2.5 samples presented a loose floc structure. In addition, the trends of variation of estimated PM_2.5 EFs derived from the MOVES simulation were essentially consistent with those of tested values.

Copyright © 2018 American Association for Aerosol Research     

Development and Evaluation of a Continuous Ambient PM2.5 Mass Monitor

A Continuous Ambient Mass Monitor (CAMM) for fine particle mass (PM_2.5) has recently been developed at the Harvard School of Public Health. The principle of this method is based on the measurement of the increase in pressure drop across a membrane filter (Fluoropore^TM) during particle sampling. The monitor consists of a conventional impactor inlet to remove particles larger than 2.5 mu m, a diffusion dryer to remove particle-bound water, a filter tape to collect particles, a filter tape transportation system to allow unassisted sampling, and a data acquisition and control unit. For each sampling period (typically 30- 60 min), a new segment of the filter tape is exposed so that particles remain close to equilibrium with the sample air during their collection. This results in mini mization of volatilization and adsorption artifacts during sampling. Furthermore, since the required flow rate for the fine particle mass monitoring channel is only 0.3 L / min, the relative humidity of the air sample can be easily reduced to 40% or less using a NafionTM diffusion dryer to remove particle-bound water. The CAMM has a detection limit of > 5 mu g / m³ for PM_2.5 concentrations averaged over 1 h. The performance of the newly developed monitor was investigated through laboratory and field studies. Laboratory tests included a calibration of the CAMM using polystyrene latex (PSL) and silica particles. A series of field studies were conducted in 7 cities with presumably different PM_2.5 chemical composition. The 24 1-h CAMM measurements were averaged and compared to Harvard Impactor (HI) 24 h PM_2.5 integrated measurements. Based on 211 valid sampling days, the measurements obtained from the Harvard Impactor and the CAMM were highly correlated (r² = 0.90). The average CAMM-to-HI concentration ratio was 1.07 (+- 0.18).     

Effects of different particle deposition parameters on adhesion of resin cement to zirconium dioxide and phase transformation

This study evaluated the effect of air-abrasion parameters such as particle size, distance, and time on adhesion of resin cement to zirconium dioxide (Y-TZP) and t→m phase transformation. Y-TZP blocks (N = 80) (In-Ceram YZ, Vita) (4 mm^3?×?4 mm^3?×?3 mm³) were assigned into eight groups (n = 10): air-abrasion with 30 μm (CoJet Sand, S30) and 110 μm (Rocatec-Plus, S110) silica-coated alumina particles, applied for either for 10–20 s (T = time), from a distance of 10–20 mm (D = distance), composing the following groups: S₃₀T₁₀D₁₀, S₃₀T₁₀D₂₀, S₃₀T₂₀D₁₀, S₃₀T₂₀D₂₀, S₁₁₀T₁₀D₁₀, S₁₁₀T₁₀D₂₀, S₁₁₀T₂₀D₁₀, and S₁₁₀T₂₀D₂₀. Resin composite (RelyX ARC) was bonded to Y-TZP blocks in polyethylene molds. The specimens were aged (10,000 thermal cycles and water storage for 90 days) prior to shear bond test. Failure types were analyzed under stereomicroscope and SEM, and phase transformation was calculated. Data (MPa) were analyzed using 3-way ANOVA and Tukey’s tests. Air-abrasion with 110 μm silica particles (10.96) presented significantly higher bond strength (p = 0.0149) compared to 30 μm (8.96). Time (p = 0.403) and distance (p = 0.179) parameters did not affect the results significantly. Air-abrasion with 110 μm particles (12.3) promoted higher bond strength than that of 30 μm (6.4) when applied for 10 s from a distance of 10 mm (Tukey’s). Failure types were predominantly adhesive. Phase transformation ranged between 30.3 and 35.9% for 30 μm particles and 23.8–43.7% for 110 μm particles. While the size of silica-coated alumina particles were more relevant parameter for resin cement adhesion to Y-TZP, time (up to 20 s) and distance (up to 20 mm) appear to be less pertinent.