Inter-comparison of low-cost sensors for measuring the mass concentration of occupational aerosols

Low-cost sensors are effective for measuring the mass concentration of ambient aerosols and second-hand smoke in homes, but their use at concentrations relevant to occupational settings has not been demonstrated. We measured the concentrations of four aerosols (salt, Arizona road dust, welding fume, and diesel exhaust) with three types of low-cost sensors (a DC1700 from Dylos and two commodity sensors from Sharp), an aerosol photometer, and reference instruments at concentrations up to 6500 µg/m³. Raw output was used to assess sensor precision and develop equations to compute mass concentrations. EPA and NIOSH protocols were used to assess the mass concentrations estimated with low-cost sensors compared to reference instruments. The detection efficiency of the DC1700 ranged from 0.04% at 0.1 µm to 108% at 5 µm, as expected, although misclassification of fine and coarse particles was observed. The raw output of the DC1700 had higher precision (lower coefficient of variation, CV = 7.4%) than that of the two sharp devices (CV = 25% and 17%), a finding attributed to differences in manufacturer calibration. Aerosol type strongly influenced sensor response, indicating the need for on-site calibration to convert sensor output to mass concentration. Once calibrated, however, the mass concentration estimated with low-cost sensors was highly correlated with that of reference instruments (R²= 0.99). These results suggest that the DC1700 and Sharp sensors are useful in estimating aerosol mass concentration for aerosols at concentrations relevant to the workplace.

© 2016 American Association for Aerosol Research     

Characteristics of traffic-induced fugitive dust from unpaved roads

The characteristics of fugitive dust emitted from vehicles traveling on unpaved dirt roads were measured using a suite of instruments including a real-time fugitive dust sampler. The fugitive dust sampler is formed from a combination of a large particle inlet and an optical particle spectrometer that reports particle sizes from 6 to 75 µm. The large particle inlet permits the sampling of particles up to 75 µm with only a moderate dependence of sampling efficiency on wind-speed. Measurements made with the sampler showed that particles as large as ～50 µm were suspended from vehicular movement on the dirt roads, with the mode of the fugitive dust particle number size distribution ～2 µm, while the mass distribution mode was ～7 µm. A comparison of the fugitive dust sampler measurements with those made using standard PM instruments showed that the conventional instruments have a wind-direction bias that can result in under-sampling of large particles. The current measurements suggest that particles suspended from dirt roadways are of importance for local air quality within the near-road environment.

Copyright © 2017 American Association for Aerosol Research     

On the Feasibility of a Number Concentration Calibration Using a Wafer Surface Scanner

A new primary standard method for calibrating optical particle counters (OPC) has been developed based on quantitative gravitational deposition on a silicon wafer and accurate counting of the particles by a wafer surface scanner (WSS). The test aerosol consists of 3-μm diameter monodisperse polystyrene latex (PSL) spheres at concentrations in the range of 0.1 cm^?3 to 1 cm^?3. A key element to the calibration is the ability to generate monodisperse PSL spheres without residue particles by use of a virtual impactor and differential mobility analyzer. The use of these devices reduced the percentage of residue particles from more than 99.98% to about 5%. The expanded relative uncertainty (95% confidence level) in the number concentration determined with a WSS for a deposition of 200 particles is 17.8%. The major uncertainty component arises from the Poisson fluctuations in the aerosol concentration because of the low concentration. This methodology has advantages of a fast scanning time by the WSS of minutes compared to hours or days by microscopy and of counting every particle deposited compared to often only a small fraction via microscopy.

The WSS was used in the calibration of an OPC based on 12 depositions with concentrations ranging from 0.1 cm^?3 to 1 cm^?3 for each deposition. Make-up air was added to the aerosol entering the OPC so that the lowest achievable concentration for the OPC measurement is about 0.01 cm^?3 in this study. The detection efficiency of the OPC was measured to be 0.984 with an expanded uncertainty of 13.4%.

Copyright 2014 American Association for Aerosol Research     

Characterizing the performance of two optical particle counters (Grimm OPC1.108 and OPC1.109) under urban aerosol conditions

The performance of Grimm optical particle counters (OPC, models 1.108 and 1.109) was characterized under urban aerosol conditions. Number concentrations were well correlated. The different lower cut-off diameters (0.25 and 0.3 μm) give an average difference of 23.5%. Both detect less than 10% of the total particle concentration (0.01–1 μm; Differential Mobility Analyzer), but in the respective size ranges, differences are <10%. OPC number size distributions were converted to mass concentrations using instrument-specific factors given by the manufacturer. Mass concentrations for OPC1.108 were 60% higher than for OPC1.109 and (in case of OPC1.109) much lower than those measured with an impactor in the relevant size range or a TSP filter. Using the C-factor correction suggested by the manufacturer, OPC1.109 underestimated mass concentrations by 21% (impactor) and by about 36% (TSP filter), which is in the range of comparability of co-located different mass concentration methods (Hitzenberger, Berner, Maenhaut, Cafmeyer, Schwarz, &; Mueller et al., 2004).     

Physical performances and kinetics of evaporation of the CIP 10-M personal sampler's rotating cup containing aqueous or viscous collection fluid

The CIP 10-M personal sampler measures worker exposure to airborne particles by collecting particles in a rotating metal cup containing a few milliliters of a collection fluid. This device is mainly used to sample microorganisms or microbial components to measure bioaerosol concentrations in various occupational environments. Aqueous liquids are generally used, but their rapid evaporation limits the duration of sampling; alternative collection fluids could alleviate this problem. Indeed, the particle-collection efficiency of the rotating cup has not been extensively studied, and the only data available relate to a discontinued model. This study aimed to measure the collection efficiency of the current rotating cup model containing an aqueous (water) or viscous (ViaTrap mineral oil) collection fluid. The kinetics of evaporation confirmed that ViaTrap does not evaporate, making 8-h sampling campaigns in constant volumes feasible. Particles with a wide range of aerodynamic diameters (between around 0.1 and 10 µm) were produced using various test rigs and mono- or polydisperse test aerosols. Both new and older cup models performed similarly, with a collection efficiency of >80% for larger particles (aerodynamic diameters >2.8 µm), progressively decreasing to around 50% for aerodynamic diameters of 2.1 µm; with aerodynamic diameters of <1 µm, the collection efficiency was generally <10%. In physical terms, collection efficiency was unaffected by the type (aqueous or viscous) or volume (between 0 and 3 mL) of collection fluid used. Bias maps indicated that the inhalable fraction may be underestimated in occupational settings, particularly with aerosols mainly composed of particles with aerodynamic diameters of less than around 3 µm.

Copyright © 2016 American Association for Aerosol Research     

Mathematical modeling and numerical simulation of surfactant delivery within a physical model of the neonatal trachea for different aerosol characteristics

Surfactant aerosol delivery in conjunction with a noninvasive respiratory support holds the potential to treat neonatal respiratory distress syndrome in a safe manner. The objective of the present study was to gain knowledge in order to optimize the geometry of an intracorporeal inhalation catheter and improve surfactant aerosol delivery effectiveness in neonates. Initially, a mathematical model capable of predicting the aerosol flow generated by this inhalation catheter within a physical model of the neonatal trachea was implemented and validated. Subsequently, a numerical study was performed to analyze the effect of the aerosol liquid droplet size and mass flow rate on surfactant delivery and on the required aerosolization time period. Experimental validation of the mathematical model showed a close prediction of the air axial velocity at the distal end of the physical model, with an absolute error between 0.01 and 0.15 m/s. Furthermore, an admissible absolute error between 0.2 and 2 µm was attained in the prediction of the aerosol mean aerodynamic diameter and mass median aerodynamic diameter in this region. The numerical study highlighted the beneficial effects of generating an intracorporeal aerosol with a mass median aerodynamic diameter higher than 4 µm and a surfactant mass flow rate above 8.93 mg/s in order to obtain effective surfactant delivery in neonates with minimal airway manipulation.

Copyright © 2017 American Association for Aerosol Research     

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     

Control of the radial distribution of chemical components in spray-dried crystalline microparticles

The process of particle formation from evaporating droplets containing more than one solute was studied. Two-component microparticles were produced using a piezoceramic dispenser with an inner diameter of 30 µm. Initial droplets had a diameter in the range of 70–85 µm and contained sodium nitrate and potassium nitrate in different molar ratios of 30:70, 50:50, and 70:30, corresponding to weight ratios of 26.5:73.5, 45.7:54.3, and 66.2:33.8, in the form of aqueous solutions with initial concentrations of 1 or 10 mg/ml. The monodisperse droplets were dried in a dry laminar gas flow with temperatures of 50°C or 100°C. Different initial conditions affected the particle formation process and the particle morphology. The diameter of the final dried microparticles ranged from 4 to 10 µm. Their density varied from 1250 to 1950 mg/ml. The formulation and process conditions determined the distribution of chemical components in the dried microparticles, especially their surface composition as determined by energy-dispersive X-ray spectroscopy. The distribution of the chemical components was theoretically explained using characteristic times for the crystallization kinetics of the drying process. It was shown that the solute that reached supersaturation first formed most of the outer shell of the microparticles.

© 2016 American Association for Aerosol Research     

Design and evaluation of an aerodynamic focusing micro-well aerosol collector

Aerosol sampling and identification is vital for the assessment and control of particulate matter pollution, airborne pathogens, allergens, and toxins and their effect on air quality, human health, and climate change. In situ analysis of chemical and biological airborne components of aerosols on a conventional filter is challenging due to dilute samples in a large collection region. We present the design and evaluation of a micro-well (µ-well) aerosol collector for the assessment of airborne particulate matter (PM) in the 0.5–3 µm size range. The design minimizes particle collection areas allowing for in situ optical analysis and provides an increased limit of detection for liquid-based assays due to the high concentrations of analytes in the elution/analysis volume. The design of the collector is guided by computational fluid dynamics (CFD) modeling; it combines an aerodynamic concentrator inlet that focuses the aspirated aerosol into a narrow beam and a µ-well collector that limits the particle collection area to the µ-well volume. The optimization of the collector geometry and the operational conditions result in high concentrations of collected PM in the submillimeter region inside the µ-well. Collection efficiency experiments are performed in the aerosol chamber using fluorescent polystyrene microspheres to determine the performance of the collector as a function of particle size and sampling flow rate. The collector has the maximum collection efficiency of about 75% for 1 µm particles for the flow rate of 1 slpm. Particles bigger than 1 µm have lower collection efficiencies because of particle bounce and particle loss in the aerodynamic focusing inlet. Collected samples can be eluted from the device using standard pipettes, with an elution volume of 10–20 µL. The transparent collection substrate and the distinct collection region, independent of particle size, allows for in situ optical analysis of the collected PM.

© 2017 American Association for Aerosol Research     

Performance evaluation of the cost-effective and lightweight Alphasense optical particle counter for use onboard unmanned aerial vehicles

Air quality monitoring using airborne platforms is rapidly gaining ground as unmanned aerial vehicles (UAVs) are becoming easier, less expensive, and safer to operate on a routine basis. To facilitate measurements of key atmospheric properties, however, efforts are still required in developing/testing miniaturized instruments for use onboard UAVs. Here, we test two commercially available cost-effective/lightweight optical particle counters (OPCs; Alphasense Model N2) capable of measuring the size distributions of airborne particles having diameters from 380 nm to 17 μm. Tests were made against a reference and recently calibrated OPC (Grimm Model 1.109) using monodisperse polystyrene spheres. All instruments were placed in a chamber in which the temperature and pressure varied in the ranges of ?5 to 23°C and 0.7 to 1.0 atm, respectively; conditions typically encountered during UAV flights. Agreement in the particle number concentrations measured by the Alphasense and the Grimm OPCs was within 40%, under all experimental conditions used in this work, when particles having sizes >1 μm were employed during the tests. Deviations higher than 50%, however, were observed when the instruments were tested with 1.0- and 0.8-μm polysterene spheres. The particle sizes reported by both Alphasense OPCs were within ± 5% with respect to the nominal polysterene spheres’ size under all operating pressures and temperatures down to 5°C. At lower temperatures, the sizing accuracy of one of the two Alphasense OPCs degraded significantly. While our findings support that the Alphasense OPCs can be used at low temperature/pressure conditions, they should be carefully tested prior the measurements to ensure good performance.

Copyright © 2018 The Authors     

A model of transient internal flow and atomization of propellant/ethanol mixtures in pressurized metered dose inhalers (pMDI)

This article reports the extension to binary propellant/excipient mixtures of the multiphase model of transient internal flow and atomization in pressurized metered dose inhalers (pMDIs) of Gavtash and colleagues for propellant-only flows. The work considers different accounts of the effect of less volatile ethanol on the saturated vapor pressure (SVP), viscosity and surface tension of HFA-based pMDI formulations. Representation of the SVP of HFA/ethanol mixtures by Raoult's law is compared with the empirical model developed by Gavtash and colleagues as well as different theoretical mixing rules for surface tension and viscosity. For initial ethanol contents ranging from 0 to 20% by mass, the temperature, pressure and spray velocity were predicted to be almost independent of ethanol concentration when using the empirical SVP model of Gavtash and colleagues. The predicted aerosol droplet size increases with increasing concentration of ethanol. These model predictions compare favorably with phase Doppler anemometry (PDA) measurements of pMDI sprays. Exploration of model predictions with different mixing rules suggest that variations of the dynamic viscosity could result in 0.7 µm droplet size change, and different surface tension models yield around 1.5 µm droplet size change. The findings of this work challenge the view that the increase of droplet size is caused by the low volatility of excipients such as ethanol. Instead, attention is focused on composition-dependent viscosity and surface tension as potential controlling parameters with significant effect on the droplet size of HFA/ethanol sprays.

Copyright © 2018 American Association for Aerosol Research     

Assessment of indoor bioaerosols using a lab-made virtual impactor

To assess indoor bioaerosols, a virtual impactor having 1 µm cutoff diameter was designed, fabricated, and evaluated with computational fluid dynamics simulation and also with laboratory test using polystyrene latex particles. Two other cutoff diameters of 635 nm and 1.5 µm were obtained by changing the inlet flow rate and the ratio of minor channel-to-inlet flow rates. In field test, the virtual impactor was operated with varying cutoff diameter and field-emission scanning electron microscope (FE-SEM) analysis was performed for each cutoff diameter to observe morphologies of indoor aerosol particles sampled at the major and minor outlet channels. Particles were sampled at both outlet channels using the SKC Button Aerosol sampler and subsequently cultured. By colony counting, it was found that 56% of cultured fungal particles and 63% of cultured bacterial particles had aerodynamic sizes smaller than 1 µm. MALDI-TOF analysis and visual inspection of culture samples were used to identify indoor bacterial and fungal species, respectively. Nearly same species of bacteria and fungi were detected both in the major and minor flow channels.

© 2017 American Association for Aerosol Research     

Emission measurements with gravimetric impactors and electrical devices: An aerosol instrument comparison

Particulate matter in the atmosphere is known to affect Earth’s climate and to be harmful to human health. Accurately measuring particles from emission sources is important, as the results are used to inform policies and climate models. This study compares the results of two ELPI?+?devices, two PM10 cascade impactors and an eFilter, in combustion emission measurements. The comparison of the instruments in a realistic setting shows what types of challenges arise from measuring an emission aerosol with unknown particle morphologies and densities, different particle concentrations and high temperature. Our results show that the PM10 cascade impactors have very good intercorrelation when the collected mass is greater than 150?µg, but below that, the uncertainty of the results increases with decreasing mass. The raw signals of two ELPI?+?devices were nearly identical in most samples, as well as the particle number concentrations and size distributions calculated from raw signals; however, transforming the current distributions into mass distributions showed variation in the mass concentration of particles larger than 1?µm. The real-time time signal measured by eFilter was similar to the total current measured by ELPI+. The eFilter and PM10 cascade impactors showed similar particle mass concentrations, whereas ELPI?+?showed clearly higher ones in most cases. We concluded that the difference is at least partially due to volatile components being measured by ELPI+, but not by the mass collection measurements.

Copyright © 2019 American Association for Aerosol Research     

Using silver as a surrogate for plutonium: An experimental study of the explosive silver aerosol source term

An experimental method is developed for the purpose of simulating plutonium aerosol source terms with conventional metals in laboratory. In this method, metal samples are aerosolized by high explosive detonation in a containment vessel. Aerosols having aerodynamic diameter (AD) less than 10 µm are then collected by a cascade impactor and analyzed by atomic absorption spectroscopy. Two sets of experiments were conducted. In the first set, five candidate metal samples (Ag, W, Sn, Ce, and V) were tested. It is found that the cumulative mass distribution of silver under certain conditions was in good agreement with that of plutonium from the Operation Roller Coaster-Double Track experiment. Thus, silver is chosen as a surrogate to simulate the plutonium aerosol source term. In the second set, silver aerosol source term was studied in detail with different test configurations. The results demonstrate that the peak of the mass-size distribution of silver is in the AD range 1.1–3.3 µm. The amount and fraction of relatively small silver aerosols decrease significantly with time due to coagulation and deposition. Interestingly, the amount of silver in aerosols could be expressed as a quadratic function of the peak detonation pressure.

© 2016 American Association for Aerosol Research     

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     

Engineered nanomaterials exposure in the production of graphene

The objective of this study was to obtain the multi-metric occupational exposure assessment to graphene family nanomaterials (GFNs) particles of workers engaged in the large-scale production of graphene. The study design consisted of the combination of (i) direct-reading instruments, used to evaluate the total particle number concentrations relative to the background concentration (time series with spatial approach) and the mean size-dependent characteristics of particles (mean diameter and surface-area concentration) and (ii) filter-based air sampling for the determination of size-resolved particle mass concentrations. The data obtained from direct reading measurement were then used to estimate the 8-h time weighted average (8-h TWA) exposure to GFNs particles for workers involved in different working tasks. Workers were generally exposed to 8-h TWA GFNs particle levels lower than the proposed reference value (40,000 particle/cm³). Furthermore, despite high short-term exposure conditions were present during specific operations of the production process, the possibility of significant exposure peaks is not likely to be expected. The estimated 8-h TWA concentration showed differences between the unexposed (<100 particle/cm³; <0.05 µg/m³) and exposed subjects (mean concentration ranging from 909 to 6438 particle/cm³ and from 0.38 to 3.86 µg/m³). The research outcomes can be of particular interest because the exposure of workers in real working conditions was assessed with a multi-metric approach; in this regard, the study suggests that workers who are directly involved in some specific working task (material sampling for quality control) have higher potential for occupational exposure than operators who are in charge of routine production work.

© 2016 American Association for Aerosol Research     

Rapid analysis of the size distribution of metal-containing aerosol

Conventional methods to measure the metallic content of particles by size are time consuming and expensive, requiring collection of particles with a cascade impactor and subsequent metals analysis by inductively coupled plasma mass spectrometry (ICP-MS). In this work, we describe a rapid way to measure the size distribution of metal-containing particles from 10 nm to 20 µm, using a nano micro-orifice uniform-deposit impactor (nano-MOUDI) to size-selectively collect particles that are then analyzed with a field portable X-ray fluorescence (FP-XRF) device to determine metal composition and concentration. The nano-MOUDI was used to sample a stainless-steel aerosol produced by a spark discharge system. The particle-laden substrates were then analyzed directly with FP-XRF and then with ICP-MS. Results from FP-XRF were linearly correlated with results from ICP-MS (R² = 0.91 for Fe and R² = 0.84 for Cr). Although the FP-XRF was unable to effectively detect Fe particles at mass per substrate loadings less than 2.5 µg effectively, it produced results similar to those from ICP-MS at a mass per substrate loadings greater than 2.5 µg.

Copyright © 2017 American Association for Aerosol Research     

Preparation of lead (Pb) X-ray fluorescence reference materials for the EPA Pb monitoring program and the IMPROVE network using an aerosol deposition method

X-ray fluorescence (XRF) is a commonly used analytical method to quantify lead (Pb), a toxic element, in atmospheric aerosol. The commercially available reference materials used for calibrating XRF do not mimic the concentrations and filter materials of particulate matter (PM) monitoring networks. In this study, we described an aerosol deposition method to generate Pb reference materials (RMs) over a range of concentrations to serve several purposes for the US Environmental Protection Agency (EPA) and Interagency Monitoring of PROtected Visual Environments (IMPROVE) monitoring networks including laboratory auditing, federal equivalency method evaluation, and calibration and quality control of XRF instruments. The RMs were generated using a laboratory-built aerosol chamber equipped with a federal reference sampler at concentration levels ranging from 0.0125 to 0.70 μg/m³. XRF analysis at UC Davis was demonstrated to be equivalent to a US and EU reference method, inductively coupled plasma—mass spectrometry (ICP-MS), for measuring Pb on RMs following a methodology described in the United States and international standards. The Pb concentrations on subsets of the RMs were verified by three other XRF laboratories with different analyzers and/or quantification methods and were shown to be equivalent to the UC Davis XRF analysis. The generated RMs were demonstrated to have short and long-term stability, satisfying an additional requirement of reference materials.

Copyright © 2016 American Association for Aerosol Research     

Characteristics of secondhand electronic cigarette aerosols from active human use

The electronic cigarette (EC) is a new source of indoor airborne particles. To better understand the impacts of secondhand vaping (SHV) emissions on indoor air quality, real-time measurements of particle size distribution, particle number concentration (PNC), fine particulate matter (PM_2.5), CO₂, CO, and formaldehyde were conducted before, during, and after 10 min EC-use among 13 experienced users in an 80 m³ room. To assess particle transport in the room, multiple sampling locations were set up at 0.8, 1.5, 2.0, and 2.5 m away from the subjects. The arithmetic mean (standard deviation) of background PNC and PM_2.5 concentrations in the room were 6.39 × 10³ (1.58 × 10²) particles/cm³ and 8 (1) μg/m³, respectively. At 0.8 m away from EC users, right after initiation of puffing, the PNC and PM_2.5 concentrations can reach a peak of ～10⁵ particles/cm³ and ～3 × 10³ µg/m³, respectively, and then dropped quickly to background levels within 20 s due to dilution and evaporation. At the 0.8 m sampling location, the mean PNC and PM_2.5 concentrations during puffing were 2.48 × 10⁴ (2.14 × 10⁴) particles/cm³ and 188 (433) µg/m³, respectively. In addition, two modes of SHV particles were observed at about 15 and 85 nm. Moreover, concentrations of SHV particles were negatively correlated with the distances to EC users. At the 1.5 m location, PNC and PM_2.5 levels were 9.91 × 10³ (1.76 × 10³) particles/cm³ and 19 (14) µg/m³, respectively. Large variations of mean PNC levels exhaled per puff were observed both within and between EC users. Data presented in this study can be used for SHV particle exposure assessment.

Copyright © 2017 American Association for Aerosol Research     

Development and evaluation of a palm-sized optical PM2.5 sensor

A new palm-sized optical PM_2.5 sensor has been developed and its performance evaluated. The PM_2.5 mass concentration was calculated from the distribution of light scattering intensity by considering the relationship between scattering intensity and particle size. The results of laboratory tests suggested that the sensor can detect particles with diameters as small as ～0.3 µm and can measure PM_2.5mass concentrations as high as ～600 µg/m³. Year-round ambient observations were conducted at four urban and suburban sites in Fukuoka, Kadoma, Kasugai, and Tokyo, Japan. Daily averaged PM_2.5 mass concentration data from our sensors were in good agreement with corresponding data from the collocated standard instrument at the Kadoma site, with slopes of 1.07–1.16 and correlation coefficients (R) of 0.90–0.91, and with those of the nearest observatories of the Ministry of the Environment of Japan, at 1.7–4.1 km away from our observation sites, with slopes of 0.97–1.23 and R of 0.89–0.95. Slightly greater slopes were observed in winter than in summer, except at Tokyo, which was possibly due to the photochemical formation of relatively small secondary particles. Under high relative humidity conditions (>70%), the sensor has a tendency to overestimate the PM_2.5 mass concentrations compared to those measured by the standard instruments, except at Fukuoka, which is probably due to the hygroscopic growth of particles. This study demonstrates that the sensor can provide reasonable PM_2.5 mass concentration data in urban and suburban environments and is applicable to studies on the environmental and health effects of PM_2.5.

Copyright © 2018 American Association for Aerosol Research