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The objective of this study is to investigate the particle effective density of aerosol measurements in a railway tunnel environment. Effective density can serve as a parameter when comparing and calibrating different aerosol measurements. It can also be used as a proxy parameter reflecting the source of particles. Effective density was determined using two different methods. Method one defined it by the ratio of mass concentration to apparent volume size distribution. Method two relied on a comparison of aerodynamic and mobility diameter size distribution measurements. The aerodynamic size range for method one was 0.006-10 µm, and for method two, it was 10-660 nm. Using the first method, a diurnal average value of about 1.87 g/cm3 was observed for the measurements with tapered element oscillating microbalance (TEOM) in tandem with aerodynamic particle sizer + scanning mobility particle sizer (SMPS), and 1.2 g/cm3 for the combination of TEOM with electrical low pressure impactor plus (ELPI+) in the presence of traffic. With method two, the effective density was 1.45 g/cm3 estimated from the size distribution measurements with ELPI + and fast mobility particle sizer (FMPS), and 1.35 g/cm3 from ELPI + in tandem with SMPS. With both calculation methods, the effective density varied for conditions with and without traffic, indicating different sources of particles. The proportion of particles with small sizes (10-660 nm) had a significant effect on the value of the effective density when no traffic was operating. The responses of different instruments to the railway particle measurements were also compared. Copyright © 2018 The Authors. Published with license by Taylor & Francis Group, LLC [ABSTRACT FROM AUTHOR]

Spectrophotometric methods developed previously to quantify the major functional groups present in oxidized organic aerosol were modified for use with sample masses typical of those collected from ambient air. In these methods, carbonyl, hydroxyl, carboxyl, and ester groups are reacted with derivatizing agents that are specific to each functional group to form strongly light absorbing derivatives, a colored peroxide solution is formed through redox chemistry, and nitrates have an inherently strong absorbance. As described here, improved detection limits are made possible by measuring absorbance using a spectrophotometer that requires only a few microliters of solution for analysis, instead of the five milliliter volume required previously when using a standard cuvette. Use of this so-called NanoPhotometer allows comparable absorbances to be obtained with much less mass by concentrating samples by more than two orders of magnitude relative to previous methods. Detection limits are approximately 0.03, 0.02, 0.3, 1, 1, and 0.07 nmoles for carbonyl, hydroxyl, carboxyl, ester, peroxide, and nitrate groups, which correspond to approximately 0.8, 0.6, 10, 40, 50, and 5 ng of each functional group. In practice, depending on the composition of functional groups, the mass required for complete analysis of moderately oxidized organic aerosol is ∼10–100 µg. The new microscale methods were shown to provide good linearity, precision, and accuracy by comparing results from the analysis of standards and aerosol formed from reaction of α-pinene and O3with results obtained using the previously developed macroscale methods. The evaluation demonstrates that the microscale methods can be used to quantify these six functional groups at low organic aerosol mass concentrations. Copyright © 2016 American Association for Aerosol Research [ABSTRACT FROM PUBLISHER]

Airflow around an eight-passenger-car subway train running in the underground tunnel at a cruise speed of 70 km/h was numerically simulated, and the trajectories of the particles that were assumed to be re-suspended from the ground or generated at the contact points between the wheels and rails were predicted. In addition, field experiments were conducted to measure airflow velocity and PM10mass concentration under a T-car (trailer car without a driving cab) during the running of a subway train in straight sections of the underground tunnel of the Seoul Subway Line 5. The numerically predicted airflow velocities agreed well with the experimental data with the error of less than 30%, and the predicted particle distribution showed a similar tendency to the experimental results. The airflow under the T-car was predicted to be relatively uniform compared to the airflow under other passenger cars. Both numerical results and experimental data signified that a lot of particles could drift under the T-car by showing a higher particle concentration in the central area of the space under the T-car than in the edge area. As a result, the space underneath the T-car is anticipated to be a good place for installing a dust-removal system. © 2016 American Association for Aerosol Research [ABSTRACT FROM PUBLISHER]

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 [ABSTRACT FROM AUTHOR]

Surface area in addition to mass concentration is increasingly being emphasized as an important metric representing potential adverse health effects from exposure to inhaled particles. Lung-deposited surface area (SA) concentrations for a variety of aerosols: coal, biomass, cigarette, incense, candle, and TiO2 were measured using an AeroTrak 9000 (TSI Incorporated) and compared with those calculated from number size distributions from a scanning mobility particle sizer (SMPS). Three methodologies to compute the SA concentrations using the International Commission on Radiological Protection's (ICRP) Lung Deposition model and an SMPS were compared. The first method calculated the SA from SMPS size distributions, while the second method used lognormal size distribution functions. A third method generated a closed-form equation using the method of moments. All calculated SMPS SA data against which the measured SA data were compared were gen-erated using the first method only; however, the SA concentrations calculated from each of the three methods demonstrated strong correlations with each other. Overall, results between measured and calculated lung-deposited SA indicated strong positive linear associations (R² 0.78 - >0.99), moderately dependent on the type of aerosol. In all cases, the measured SA concentrations slightly underestimated those calculated from the SMPS data, with the ex-ception of coal combustion particles. Although some dependency on aerosol material exists, the instrument measuring lung-deposited SA demonstrated consistent reliability across a range of concentra-tions for a range of materials. For optimal results however, applying a correction factor (CF) before taking the instrument to the field is recommended. [ABSTRACT FROM AUTHOR]

Copyright 2013 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]