WARREN FINLAY Pengarang

Absence of any effect of the electric charging state of particles below 10 nm on their penetration through a metal grid Manuel Alonso National Center for Metallurgical Research (CENIM-CSIC), Avenida Gregorio del Amo, Madrid, Spain A B S T R A C T The effect of image force on the penetration of nanometer particles through metal grids remains a controversial issue. Experimental evidence of the existence and of the absence of such effect have both been reported in the past. A careful experimental work to measure penetration of particles in the mobility equivalent diameter range between 3.4 and 10 nm has been carried out. The possible particle size change between the aerosol generator and the fi lter has been considered, as well as the possible effect of particle number concentration on the fi ltration effi ciency. The geometric dimensions of the fi lter allowed attainment of the fully developed parabolic fl ow velocity profi le upstream the grid. Measurements were done at two values of the fi ber Reynolds number, 0.09 and 0.12, much smaller than 1, as demanded by the currently accepted fi ltration theory. Penetration of charged particles, measured in three alternative ways, has been compared with penetration of uncharged and neutral particles (the latter consisting of a mixture of positive, negative, and uncharged particles). Two main conclusions have been reached: (1) the charging state of the particles does not affect their penetration through the metal grid and (2) the experimentally measured penetrations are fairly well predicted by the fan fi lter model of Cheng and Yeh. Aerosol diffusion battery: The retrieval of particle size distribution with the help of analytical formulas A. A. Onischuka,b,c, A. M. Baklanova, S. V. Valiulina,c, P. P. Moiseenkoa,d, and V. G. Mitrochenkoa,d aVoevodsky Institute of Chemical Kinetics and Combustion, Russian Academy of Sciences, Novosibirsk, Russia; bNovosibirsk State University, Novosibirsk, Russia; cNovosibirsk State Pedagogical University, Novosibirsk, Russia; dAerosol Instruments Ltd., Novosibirsk, Russia A B S T R A C T A new algorithm is proposed for the determination of aerosol particle size distribution from a set of screen diffusion battery penetrations. The idea is to determine the size spectra of the fractions of particles separated by the sections of diffusion battery, so the total size distribution is the sum of the spectra of fractions. The spectrum of each fraction is approximated by the lognormal function, which is defined by two parameters: the standard geometric deviation (SGD) and geometric mean diameter. The SGD value is chosen to be 1.35 for each fraction. The geometric mean diameters of fractions are calculated from the diffusion battery penetrations. For this purpose, analytical formulas are derived to link the mean single-fiber collection efficiency for each fraction with the experimentally measured penetrations. Then the mean diameters of fractions are calculated from the collection efficiencies using the fan model filtration theory. To achieve a better size resolution, numerical approach is proposed to calculate the particle size spectrum using the analytical solution as an initial approximation. The validity of the analytical and numerical solutions is investigated by comparing them with the spectra determined by means of transmission electron microscopy and gravity settling. For this purpose, the aerosol is generated using the evaporation-nucleation technique, Collison-type nebulizer, and hot-wire bulb generator. It is found that the analytical solution demonstrates a good sizing accuracy but relatively poor size resolution, while the numerical approach results in both good sizing accuracy and good size resolution for the two-mode aerosol. Analytical expression for the rotational friction coeffi cient of DLCA aggregates over the entire Knudsen regime James Corsona, George W. Mulhollanda, and Michael R. Zachariaha,b aDepartment of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland, USA; bDepartment of Chemistry and Biochemistry, University of Maryland, College Park, Maryland, USA A B S T R A C T We apply a self-consistent field method (Corson et al. 2017c) to calculate the rotational friction coefficient for fractal aerosol particles in the transition flow regime. Our method considers hydrodynamic interactions between spheres in a rotating aggregate due to the linear velocities of the spheres. Results are consistent with electro-optical measurements of soot alignment. Calculated rotational friction coefficients are also in good agreement with continuum and free molecule results in the limits of small (Kn D 0.01) and large (Kn D 100) primary sphere Knudsen numbers. As we previously demonstrated (Corson et al. 2017b) for the translational friction coefficient, the rotational friction coefficient approaches the continuum limit as either the primary sphere size and the number of primary spheres increases. We apply our results to develop an analytical expression Equation (26) for the rotational friction coefficient as a function of the primary sphere size and number of primary spheres. One important finding is that the ratio of the translation to rotational diffusion times is nearly independent of cluster size. We include an extension of previous scaling analysis for aerosol aggregates to include rotational motion. Cloud condensation nuclei activity and droplet formation of primary and secondary organic aerosol mixtures E. A. Fofi e a,b, N. M. Donahue c, and A. Asa-Awuku a,b,* aDepartment of Chemical and Environmental Engineering, Bourns College of Engineering, University of California, Riverside, California, USA; bBourns College of Engineering, Center for Environmental Research and Technology (CE-CERT), Riverside, California, USA; cCenter for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, Pennsylvania, USA A B S T R A C T Understanding the mixing behavior of anthropogenic primary and biogenic secondary organic aerosol (POA and SOA) is important for characterizing their interactions with water vapor. The following work expands upon previous studies and investigates cloud condensation nuclei (CCN) activity and droplet kinetics of a-pinene SOA formed in an environmental chamber and mixed with diesel or motor oil-diesel fuel POA. The changes in the aerosol mixing are similar to previously published work but this study provides new CCN activity and droplet information. The CCN activity of the unmixed aerosol systems are measured separately; k D 0.15, 0.11, 0.022 for a-pinene SOA, diesel POA and motor oil-diesel fuel POA, respectively. In the a-pinene SOA C diesel POA mixture, the CCN activity, characterized by k-hygroscopicity, decreases from k D 0.15 to 0.06 after an initial injection of the POA but increases to k D 0.12. The increase in CCN activity occurs after particle collision (coagulation and wall-loss) rates dominate aerosol processes in the chamber. The a-pinene SOA C motor oil-fuel POA does not readily mix and the CCN activity of the complex system increases with time (from k D 0.022 to 0.10). An empirical equation using unit mass resolution (UMR) AMS data of two different ion fragments reasonably predicts CCN activity of the POA and SOA mixtures. CCN measurement may be a promising tool to gain additional insight into the complex mixtures of organic aerosol and subsequent interactions with water vapor. Design and evaluation of a low fl ow personal cascade impactor Modi Chen, Francisco J. Romay, and Virgil A. Marple MSP Corporation, Shoreview, Minnesota, USA A B S T R A C T A very compact cascade impactor with 2 L/min sampling fl ow rate has been developed. Its dimensions are 8.5 cm L x 5.0 cm W x 11.4 cm H, and it weighs 0.27 kg, with ten impaction stages with aerodynamic cutpoints in the range of 60 nm to 9.6 mm. The top eight stages, collecting particles down to 170 nm in aerodynamic diameter, can be used as a stand-alone impactor with a portable, battery-powered pump. Particle collection efficiencies were obtained with two types of commonly used substrates, aluminum foil and glass fiber filters. Impactor cutpoints with aluminum foil substrates agree well with conventional impactor theory. The efficiency curves are sharp with minimum overlap between them. Thus, the compact impactor design does not compromise its performance, making it suitable for general purpose applications where a lower sampling flow rate provides adequate mass collection. With glass fiber filter substrates, impactor cutpoints are smaller and the efficiency curves are less steep, in particular for the last stages. Also, the collection efficiency curves do not drop to near zero at small Stokes numbers. Instead, excess particle collection efficiency of around 10% is observed for the top six stages, and becomes higher for the last four stages. This is due to the collection of particles by filtration as the impinging jets penetrate the filter substrate. Thus, using glass fiber filter substrates should generally be avoided due to the non-ideal effect on the impactor collection efficiency curves, especially for the last two stages. Direct measurement of aerosol glass fi ber alignment in a DC electric fi eld Bon Ki Ku, Gregory Deye, and Leonid A. Turkevich Centers for Disease Control and Prevention (CDC), National Institute for Occupational Safety and Health (NIOSH), Division of Applied Research and Technology, Cincinnati, Ohio, USA A B S T R A C T We report non-conducting aerosol fi ber (i.e., glass fi ber) alignment in a DC electric fi eld. Direct observation of fi ber orientation state is demonstrated and quantitative analysis of fi ber alignment is made using phase contrast microscopy in four different conditions: (i) dry air and naturally charged fibers, (ii) humid and naturally charged, (iii) humid and neutralized (Boltzmann charge distribution), and (iv) humid and neutralized with an electrostatic precipitator upstream electrodes (i.e., noncharged). The glass fi ber aerosols generated by a vortex shaking method were conditioned using a Po-210 neutralizer or humidifi er and were provided into a test unit where cylindrical or parallel plate electrodes are used and high voltage is applied to them. Fibers were collected on a fi lter immediately downstream from the electrodes and their images were taken through an optical microscope to visualize the fi ber orientation and measure the alignment angles and lengths of the fibers. The results showed that under all four conditions tested, airborne glass fi bers could be aligned to the electric fi eld with different alignment quality, indicating that the glass fi bers can be polarized in a steady electric fi eld. In humid air, the fi ber alignment along the fi eld direction was observed to be much better and the number of uniform background particles (i.e., randomly oriented fi bers) in angular distributions is smaller than that in dry air. Also, it was found that charged fi bers in humid air could be better aligned with negligible uniform background than neutralized and non-charged fi bers. Possible mechanisms about humidity and charge effects on enhanced fi ber alignment are discussed to support the observations. The results indicate that the enhancement of alignment in an electric fi eld would be possible in humid air for other nonconducting fi brous particles having surface chemistry similar to glass fi bers.