Development and evaluation of a palm-sized optical PM2.5 sensor
Tomoki Nakayamaa, Yutaka Matsumia, Keiko Kawahitob, and Yoshifumi Watabeb
aInstitute for Space-Earth Environmental Research, Nagoya University, Nagoya, Aichi, Japan; bEco Solutions Company, Panasonic Corporation, Kadoma, Osaka, Japan
A B S T R A C T
A new palm-sized optical PM2.5 sensor has been developed and its performance evaluated. The PM2.5 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 mm and can measure PM2.5mass concentrations as high as »600 mg/m3. Year-round ambient observations were conducted at four urban and suburban sites in Fukuoka, Kadoma, Kasugai, and Tokyo, Japan. Daily averaged PM2.5 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 PM2.5 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 PM2.5 mass concentration
data in urban and suburban environments and is applicable to studies on the environmental and health effects of PM2.5.
Effects of operational mode on particle size and number emissions
from a biomass gasifi er cookstove
Jessica Tryner, John Volckens, and Anthony J. Marchese
Department of Mechanical Engineering, Colorado State University, Fort Collins, Colorado, USA
A B S T R A C T
Interest in the size distribution of particles emitted from biomass cookstoves stems from the hypothesis that exposure to ultrafi ne particles is more detrimental to human health than exposure to accumulation mode or other size regimes. Previous studies have reported that gasifi er cookstoves emit smaller particles than other cookstove designs under steady operating conditions. In the present study, the number size distribution of particles emitted from a forced-air gasifier cookstove was measured at 1 Hz as the stove transitioned between several steady and transient operating modes. During normal operation, when the stove functioned as a top-lit updraft gasifier, the distribution was bimodal, with peaks at 10 nm and 40 nm, when a pot of water was on the stove. The distribution became unimodal with a peak at 10 nm when the pot was removed. Once the fuel bed had completely gasifi ed and the secondary fl ame extinguished, the concentration of particles increased and the peak in number concentration shifted to approximately 80 nm. After refueling, when the stove operated as a conventional updraft gasifi er, the peak in number
concentration decreased to 10 nm. When the secondary fl ame extinguished a second time, the peak in number concentration increased to approximately 100 nm before decreasing to 20 nm during the char burn-out phase. These results demonstrate that changes in operational mode infl uence the combustion process and produce distinct changes in the size distribution and rate of
particle emissions.
Estimation of acoustic forces on submicron aerosol particles in a standing
wave fi eld
Ramin J. Imani a and Etienne Roberta,b
aKTH Royal Institute of Technology, Department of Mechanics, Stockholm, Sweden; bPolytechnique Montreal, Department of Mechanical Engineering, Montreal, Quebec, Canada
A B S T R A C T
The net acoustic force acting on submicron particles suspended in a gas and exposed to a standing wave field is investigated as a function of particle size, by measuring both the aerosol number density and size distribution in a flow-through resonator. By taking into account all contributions relevant to the net force, this experimental study provides a first estimate for the acoustic radiation force in a size range where molecular effects are expected to be significant. The experiment consists of an electrostatic transducer generating a standing wave in the 50–80 kHz frequency range, with the submicron aerosol particles concentrated at pressure antinodes located across the height of a rectangular channel. A section of the flow is sampled isokinetically and analyzed using a Scanning Mobility Particle Sizer (SMPS), while the nodal patterns are visualized simultaneously using light scattering. The net acoustic force is calculated from their measured displacement along the axis of the 1D standing wave field. The component of this force resulting from radiation pressure is estimated by subtracting contributions from other forces. The results provide the first experimental estimation of the size dependence of the acoustic contrast factor for submicron aerosol particles,
demonstrating the possibility of performing acoustic separation for diameters as small as 150 nm.
Exploring CCN droplet suppression with a higher sensitivity optical particle
counter
Emmanuel Fofi ea,b, Vincent Castellucciob,c, and Akua Asa-Awukua,b,d
aDepartment of Chemical and Environmental Engineering, Bourns College of Engineering, University of California, Riverside, CA, USA; bBourns College of Engineering, Center for Environmental Research and Technology (CE-CERT), Riverside, CA, USA; cNow at the Naval Surface Warfare Center, Corona, CA, USA; dNow at the Department of Chemical and Biomolecular Engineering, A. James Clark School of Engineering, University of Maryland, College Park, MD, USA
A B S T R A C T
The continuous flow thermal gradient cloud condensation nuclei counter (CCNc) is the instrument currently widely used in exploring the interactions of aerosol with water vapor in the supersaturated regime. In this study we use a CCNc with an optical particle counter (OPC) modified to twice the sensitivity of the default OPC on the standard CCNc built by DMT, Inc. The standard OPC and the modified OPC-b are used to explore the droplet growth of inorganic and organic salts and the effects of
cloud condensation nuclei concentrations on the final droplet sizes. We also couple the higher sensitivity OPC-b with the continuous flow streamwise thermal gradient CCNc (CFSTGC) model to estimate the mass accommodation coefficient, a. For inorganic and organic aerosol, a mass accommodation coefficient, a >> 0.2 will yield modeled droplet diameters consistent with experimental and ambient observations. However, using higher sensitivity CCN data, the final droplet diameters of CCN appear
independent of aerosol hygroscopicity but strongly dependent on the CCN concentration. The final droplet diameters are suppressed by » 0.2 mm for every 1000 cm ¡ 3 CCN, even at CCN concentrations less than 5000 cm ¡ 3. Our current understanding of aerosol CCN formation and droplet kinetics may therefore be dependent on the sensitivity of the optical particle counter in the CCNc
Opto-aerodynamic focusing of aerosol particles
Yong-Le Pana, Aimable Kalumea, Chuji Wangb, and Joshua L. Santarpiac
aU.S. Army Research Laboratory, Adelphi, MD, USA; bMississippi State University, Starkville, MS, USA; cSandia National Laboratories, Albuquerque, NM, USA
A B S T R A C T
We describe a new method for focusing and concentrating a stream of moving micron-sized aerosol particles in air. The focusing and concentrating process is carried out by the combined drag force and optical force that is generated by a double-layer co-axial nozzle and a focused doughnutshaped hollow laser beam, respectively. This method should supply a new tool for aerosol science
and related research.
Particulate matter characteristics, dynamics, and sources in an underground mine
S. Saarikoskia, K. Teinil€aa, H. Timonena, M. Aurelaa, T. Laaksovirtaa, F. Reyesb, Y. Vasquesb, P. Oyolab, P. Artaxoc, A. S. Pennanend, S. Junttilae, M. Linnainmaaf, R. O. Salonend, and R. Hillamoa
aAtmospheric Composition Research, Finnish Meteorological Institute, Helsinki, Finland; bCentro Mario Molina Chile, Santiago de Chile, Chile; cDepartment of Applied Physics, University of S~ao Paulo, Rua do Mat~ao, S~ao Paulo, Brazil; dDepartment of Health Security, National Institute for Health and Welfare, Kuopio, Finland; eOutokumpu Stainless Ltd, Ter€astie, Tornio, Finland; fWork Environment, Finnish Institute of Occupational Health, Tampere, Finland
A B S T R A C T
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 mm 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 timeresolution and offline particulate sampling followed by elemental and ionic analyses. A majority of sub-micrometer particles (<1 mm 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 mm 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.
Ring-shaped deposition patterns in small nozzle-to-plate distance impactors
S. Fredericks and J. R. Saylor
Department of Mechanical Engineering, Clemson University, Clemson, SC, USA
A B S T R A C T
Experiments were carried out in an impactor, where the distance between the impactor nozzle and the impactor plate was small, much less than one nozzle diameter in separation. The aerosol deposition patterns in this impactor were investigated for aerosols in the 3– 15 mm diameter range. Ring-shaped deposition patterns were observed where the internal diameter and thickness of the
rings were a function of the particle diameter. Specifically, the inner diameter and ring thickness were correlated to the Stokes number, Stk; the ring diameter decreased with Stk, and the ring thickness increased with Stk. At Stk » 0:4 the ring closed up, leaving a mostly uniform disk deposition pattern. These ring patterns do not appear to correspond to patterns previously described in the literature, and an order of magnitude analysis shows that this is an inertially dominated process.
Size-selective sampling performance of six low-volume “ total” suspended
particulate (TSP) inlets
Robert W. Vanderpoola, Jonathan D. Krug a, Surender Kaushika, Jerome Gilberryb,c, Andrew Dartb,
and Carlton L. Witherspoonc
aUS EPA, North Carolina, USA; bRTI International, North Carolina, USA; cAlion Science and Technology, North Carolina, USA
A B S T R A C T
Several low-volume inlets (flow rates 16.7 liters per minute (Lpm)) are commercially available as components of low-cost, portable ambient particulate matter samplers. Because the inlets themselves do not contain internal fractionators, they are often assumed to representatively sample “total” mass concentrations from the ambient air, independent of aerodynamic particle size and wind speed. To date, none of these so-called “TSP” inlets have been rigorously tested under controlled conditions. To determine their actual size-selective performance under conditions of expected use, wind tunnel tests of six commonly used omnidirectional, low-volume inlets were conducted using solid, polydisperse aerosols at wind speeds of 2, 8, and 24 km/h. With the exception of axially-oriented, isokinetic sharp-edge nozzles operating at 5 and 10 Lpm, all lowvolume inlets showed some degree of nonideal sampling performance as a function of aerodynamic particle size and wind speed. Depending upon wind speed and assumed ambient particle size distribution, total mass concentration measurements were estimated to be negatively biased by as much as 66%. As expected from particle inertial considerations, inlet efficiency tended to degrade with increasing wind speed and particle size, although some exceptions were noted. The implications of each inlet’s non-ideal behavior are discussed with regards to expected total mass concentration measurement during ambient sampling and the ability to obtain representative
sampling for size ranges of interest, such as PM2.5 and PM10. Overall test results will aid in lowvolume inlet selection and with proper interpretation of results obtained with their ambient field use.
Studies on detachment behavior of micron sized droplets: A comparison between
pure fl uid and nanofl uid
S. C. Fua, Y. S. Cheunga, H. H. Leea, Joseph K. C. Kwanb,c, and Christopher Y. H. Chaoa
aDepartment of Mechanical and Aerospace Engineering, The Hong Kong University of Science and Technology, Hong Kong; bDivision of Environment and Sustainability, The Hong Kong University of Science and Technology, Hong Kong; cHealth, Safety & Environment Office, The Hong Kong University of Science and Technology, Hong Kong
A B S T R A C T
Resuspension is considered as a source of indoor air pollutants. These airborne pollutants can be in the form of liquid or solid. It has been previously found that the detachment mechanism of liquid droplets is different from the solid particles on the poly(methyl methacrylate) (PMMA) surface. Liquid droplets detach by portion when they are under an increasing normal force field while droplets detach completely when under a tangential force field. In this research, droplet detachment experiments are extended to different substrate materials, which are PMMA, glass, and stainless steel by the means of centrifuge. Also, the differences in detachment between pure glycerol-water (pure fluid) and a glycerol solution with the addition of nanoparticles (nanofluid) are investigated under different substrate materials. It is found that liquid droplets, again, detach by portion under normal force for all the substrate materials. For tangential force, the droplets detach completely if the exerted force was sufficiently large and the threshold values are material dependent, which is further elaborated by retention theory. After the addition of nanoparticles, a higher removal force was required compared to the droplets of pure fluid within the same size range. Also, solid residues with a negligible amount of fluid were found on the substrate after each removal of droplets under both normal and tangential force. The involvement of nanoparticles could be the pioneer work for future studies on commonly found liquid pollutants, which are prone to be contaminated by solid particles, such as in salivary excretion.
Surgical smoke simulation study: Physical characterization
and respiratory protection
Yousef Elmashaea, Richard H. Koehlerb, Michael Yermakova, Tiina Reponena, and Sergey A. Grinshpuna
aCenter for Health-Related Aerosol Studies, Department of Environmental Health, University of Cincinnati, PO Box 670056, Cincinnati, OH, USA; bDepartment of Surgery, Martha’s Vineyard Hospital, 1 Hospital Rd, Oak Bluffs, MA 02557, USA
A B S T R A C T
Exposure of operating room (OR) personnel to surgical smoke, a unique aerosol generated from the common use of electrocautery during surgical procedures, is an increasing health risk concern. The main objective of this simulation study was to characterize the surgical smoke exposure in terms of the particle number concentration and size distribution in a human breathing zone. Additionally, the performance of respiratory protective devices designed for ORs was examined using two commercially available N95 facepiece filtering respirators (FFRs) as well as the same FFRs modified with new faceseal technology. The tests were conducted in an OR-simulating exposure chamber with the surgical smoke generated by electrocautery equipment applied to animal tissue and measured in the breathing zone with four aerosol spectrometers. The simulated workplace protection factor of each tested respirator was determined for ten subjects by measuring the total aerosol concentrations inside and outside of a respirator. The peak of the particle size distribution was in a range of 60–150 nm. The concentration of particles generated during the simulated surgical procedure significantly exceeded the background concentration under all tested air exchange conditions. The data suggest that wearing N95 filtering facepiece respirators significantly decreased the human exposure to surgical smoke. The new faceseal technology provided significantly higher respiratory protection than the commercial N95 FFRs.
The accuracy of the aerosol particle mass analyzer for nanoparticle classification
Bo-Xi Liao, Neng-Chun Tseng, and Chuen-Jinn Tsai
Institute of Environmental Engineering, National Chiao Tung University, Hsin Chu, 300, Taiwan
A B S T R A C T
The aerosol mass measurement method, DMA-APM, measures a lower mass as compared to the electrical mobility diameter-based particle mass for sub-50 nm nanoparticles. The extent of underestimation increases with decreasing nanoparticle diameter and can reach as much as 20–80% for different nanoparticles between 10– 20 nm. To study this issue, the DMA-APM system was
tested with traceable size standards (PSL and NanoSilica) and laboratory generated silver nanoparticles. It was found that the extent of mass underestimation depended on Brownian diffusion as well as the strength of the classifying forces, and the extent was quantifi ed by a dimensionless parameter λ c; P, which is suggested to be higher than 40 to eliminate the mass underestimation for size standards. Further analysis also showed that the uncertainty in the particle density of test nanoparticles should be as low as possible to minimize the error in the judgment on the accuracy of the APM. Finally, the absolute accuracy of the APM at different λc;P was determined by the size standards, which could be used to correct for the mass underestimation for sub-50 nm
nanoparticles.
Volume changes upon heating of aerosol particles from biomass burning
using transmission electron microscopy
Kouji Adachia, Arthur J. Sedlacek IIIb, Lawrence Kleinmanb, Duli Chandc, John M. Hubbec, and Peter R. Buseckd
aAtmospheric Environment and Applied Meteorology Research Department, Meteorological Research Institute, Tsukuba, Japan; bEnvironmental and Climate Sciences, Brookhaven National Laboratory, Upton, NY, U.S.A; cAtmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, WA, USA; dSchool of Earth and Space Exploration & School of Molecular Sciences; Arizona State University, Tempe, AZ, U.S.A.
A B S T R A C T
The responses of aerosol particles to heating are important for measurements of their chemical, physical, and optical properties, classification, and determination of origin. However, the thermal behavior of organic aerosol particles is largely unknown. We provide a method to analyze such thermal behavior through heating from room temperature to >600 C by using a heating holder
within a transmission electron microscope (TEM). Here we describe in-situ shape and size changes and variations in the compositions of individual particles before and after heating. We use ambient samples from wildland and agricultural biomass fires in North America collected during the 2013 Biomass Burning Observation Project (BBOP). The results indicate that individual tar balls (TB; spherical organic material) from biomass burning retained, on average, up to 30% of their volume when heated to 600 C. Chemical analysis reveals that K and Na remain in the residues, whereas Sa nd O were lost. In contrast to bulk sample measurements of carbonaceous particles using thermal/optical carbon analyzers, our single-particle results imply that many individual organic particles consist of multiple types of organic matter having different thermal stabilities. Beyond TBs, our
results suggest that because of their thermal stability some organic particles may not be detectable by using aerosol mass spectrometry or thermal/optical carbon analyzers. This result can lead to an underestimate of the abundance of TBs and other organic particles, and therefore biomass burning may have more influence than currently recognized in regional and global climate models.
