Scanning Mobility Particle Sizer Research Articles

Open-hardware design and characterization of an electrostatic aerosol precipitator

Electrostatic precipitators are devices that remove charged particles from an air stream. We present the design and characterization of an electrostatic precipitator that is intended to be incorporated into aerosol sampling equipment. Hardware and software components of the design are open, all components can be directly purchased from vendors, and the device can be assembled with standard tools. Generic components are used to allow the repurposing of parts for other uses. The computer-controlled high-voltage power supply box associated with the project can be used for other common high-voltage applications in Aerosol Science and Technology, such as data acquisition and control systems for scanning mobility particle sizers. Computational fluid dynamics simulations are used to quantify the 3D flow field. The transfer function associated with the partial transmission is characterized through modeling and experiments. The observed transfer function is unique but deviates from the ideal transfer function due to the distortion of the flow near the inlet and the outlet of the device. Singly charged particles up to 624 nm and 253 nm can be completely removed for 0.5 L min−1 and 1 L min−1, respectively. We anticipate that our device will increase the accessibility of the technique to a broader audience.

Online analysis of chemical composition and size distribution of fresh cigarette smoke emitted from a heated tobacco product

Online analysis of chemical composition of cigarette smoke of a heated tobacco product (HTP) was performed by using a home-made vacuum ultraviolet (VUV) lamp-based photoionization time-of-flight (TOF) mass spectrometer. A capillary inlet and an aerodynamic lens were utilized to sample the gas- and particulate-phase of the HTP smoke, without dilution and pretreatment, which can be switched from each other within minutes. A thermal desorption unit was installed to vaporize the particulate-phase into gas and its vaporization temperature was determined, based on an equilibrium between the evaporation efficiency and the thermal decomposition of organic compounds. Then these species were softly ionized by VUV photons and their ions were measured by a reflectron TOF mass analyzer. Meanwhile, the puff-by-puff resolved size distributions of the HTP smoke were probed with a commercial scanning mobility particle sizers (SMPS). The mean diameters of particles firstly increase with the puff number, mainly located in the range of 200 – 300 nm, and then approached a steady state. This method was validated to measure the physical-chemical characteristics of the HTP cigarette smoke.•A capillary inlet and an aerodynamic lens were utilized to sample the gas- and particulate-phase of the HTP smoke.•Chemical composition of the HTP smoke was measured by using a compact VUV photoionization mass spectrometer.•The particle size distribution of the HTP smoke without dilution was measured online.

Application of an Electrospray Scanning Mobility Particle Sizer to Mixed Abrasive Slurry for Chemical Mechanical Planarization

Application of an Electrospray Scanning Mobility Particle Sizer to Mixed Abrasive Slurry for Chemical Mechanical Planarization

Vertical profile of aerosol number size distribution during a haze pollution episode in Hefei, China

The vertical distribution of aerosols has important implications on haze formation as development, which is manifested to some extent by the planetary boundary layer (PBL)–aerosol interactions. Information on the number concentration and size of particles is essential to understand these processes, but studies on vertical profiles of particle number-size distribution are limited. Herein, an unmanned aerial vehicle (UAV) equipped with a custom-built optical particle counter (0.4–10 μm) was used to investigate the vertical profiles of particle number-size distribution in Hefei (China) during January 20–30, 2021. Combining ground-based scanning mobility particle sizer and meteorological data, the pollution accumulation and diffusion mechanisms were analyzed in depth. Results showed that as the pollution episode developed, the vertical distribution of the particle number concentration changed from a flat profile to a sharp vertical gradient. Under polluted conditions, a three-layer structure was clearly evident: uniform distribution in a mixed layer near the ground, a sharply reduced transition layer, and a low number concentration layer in the free atmosphere. Analysis revealed that fundamental to this conversion is that aerosols are highly affected by the PBL dynamics. Concurrent on-UAV and ground-based observations revealed that the ratio of particle numbers in the accumulation mode to that in the Aitken mode was 0.92 ± 0.05 in polluted days, which was almost three times that of clean days. This difference in the ratio of large to small particles suggests that hygroscopic growth of aerosol particles under high humidity conditions played an important role in haze development. Moreover, the sharp vertical gradient of the particle number concentration in the transition layer was identified as an important parameter for characterizing PBL height. The findings in this study highlight the importance of PBL dynamics on the under-studied vertical profiles of particle number-size distribution, especially during heavy pollution episodes.

Promotion of particle formation by resonance-stabilized radicals during hydrocarbon pyrolysis

We measured aerosol mass spectra and mobility size distributions of particles formed during the pyrolysis of ethylene, indene, and a mixture of ethylene with a small amount of indene. Measurements were recorded with a scanning mobility particle sizer and an aerosol mass spectrometer employing vacuum ultraviolet photoionization using tunable radiation from the Advanced Light Source at Lawrence Berkeley National Laboratory. The results demonstrate that particle formation occurs at a temperature of ∼1123±50 K for ethylene alone, at ∼923±50 K for indene alone, and at a comparable temperature to that of indene for ethylene seeded with a small amount of indene. Our results demonstrate that indene and indenyl, a resonance-stabilized radical (RSR) formed from indene pyrolysis, promote particle formation at lower temperatures and in the absence of acetylene, supporting the hypothesis that RSRs promote soot-particle inception. Even a small amount of indene added to ethylene promotes particle formation while circumventing the traditional pathways for mass growth by acetylene-addition reactions. Further support is provided by the appearance in the aerosol mass spectra of prominent peaks for masses corresponding to other RSRs from particles formed at lower pyrolysis temperatures. In addition, odd-numbered carbon species, associated with RSRs, appear in higher concentrations at low temperatures and are closely tied to particle inception. In indene pyrolysis, mass signals indicative of covalently bound indenyl dimers and trimers are prominent at pyrolysis temperatures near soot onset. Photoionization efficiency (PIE) curves demonstrate that, while the isomeric composition for some of these peaks may differ between ethylene and indene, the addition of indene to ethylene does not notably alter the isomers formed at these peaks between ethylene and the ethylene-indene mixture. PIE curves also show that m/z 202, which is commonly assumed to be pyrene, is composed principally of fluoranthene under these conditions.

Characteristics of ultrafine particles emitted from 3D-pens and effect of partition on children's exposure during 3D-pen operation.

A three-dimensional (3D) printing pen is a popular writing instrument that uses a heated nozzle, and is similar to a 3D-printer. Processing thermoplastic filaments with a 3D-pen can emit ultrafine particles (UFPs). 3D-pen education sessions were held with "∏"-shaped partitions for the prevention of coronavirus disease (COVID-19). This study aimed to characterize UFP emissions from two types of 3D-pens and evaluate the influence of "∏"-shaped partitions on UFP exposure. Measurements of UFP emission rates and the size distribution of particles emitted from 3D-pens were conducted in a chamber (2.5m3 ). The partition's influence on UFP exposure was evaluated with and without a "∏"-shaped partition on a desk. A scanning mobility particle sizer (SMPS) and an optical particle spectrometer (OPS) were used to measure the particle number concentration (PNC) and size distribution. For both 3D-pen A and B, the average emission rates were statistically significantly highest for acrylonitrile butadiene styrene (ABS) filament (8.4×106 [3.4] particles/min and 1.1×106 [1.8] particles/min), followed by polylactic acid (PLA) (2.8×105 [1.5] particles/min and 4.8×104 [1.8] particles/min) and polycaprolactone (PCL) filaments (1.4×104 [2.8] particles/min and 2.0×104 [2.8] particles/min). For all filaments, particles in the Aitken mode (30-100nm) accounted for the highest proportion. In 3D-pen A, PNCs were higher with the partition than without it for ABS (1.2×106 [1.15] particles/cm3 vs. 1.4×105 [1.29] particles/cm3 ) and PLA (6.2×105 [1.38] particles/cm3 vs. 8.9×104 [1.12] particles/cm3 ), whereas for 3D-pen B, they were higher with the partition for ABS (9.6×105 [1.13] particles/cm3 vs. 4.9×105 [1.22] particles/cm3 ) only. With the partition installed, PNCs decreased to the background level after the operation ended, whereas it took 2-6min without the partition. However, the mass concentrations of PLA and PCL with 3D-pen A were not statistically significantly different with respect to the partition status. The use of 3D-pens with a partition can lead to high UFP exposure. Therefore, guidelines are required for the safe use of 3D-pens and partitions.

Ash Aerosol and Deposit Formation from Combustion of Coal and Its Blend with Woody Biomass at Two Combustion Scales: Part 1─1.5 MWTH Pilot-Scale Combustor Tests

There is great interest worldwide in repurposing electric utility boilers designed to fire pulverized coal to fire, instead woody biomass or blends of woody biomass with coal. In this investigation, two prepared biomass/coal blends and the pure parent coal were fired in a 1500 kW pulverized coal combustor with a primary objective of elucidating the mineral particle behavior. The results reported here, although complete in themselves, comprise the first part of a two-part systematic study to investigate the effects of combustion scale on ash deposition rates at scales of 1500 kW (this study), and 1.2 × 106 kW (471 MWe) using identical coal and coal/biomass fuels and similar analytical techniques. The woody biomass of interest was composed of materials collected in a Utah National Forest and was prepared using a torrefaction technique (for both combustion scales) and a separate steam explosion technique (for the 1500 kW pilot scale only, described here). Biomass samples were blended in 15 wt % biomass with a Utah bituminous coal and were pulverized along with samples of pure coal at a specification of 70 wt % passing through 200 mesh. To sample entrained and deposited mineral matter, a water-cooled extractive probe for ash aerosol and an air-cooled ash deposit probe were designed, constructed, and implemented. The probes were inserted into sample ports at gas temperatures in the range of 1200–1370 K with a deposit coupon surface temperature of 811 K, conditions representative of a utility boiler vertical reheater and of a fouling deposit mechanism. Aerosol size distributions were determined using a scanning mobility particle sizer (SMPS) and an aerodynamics particle sizer (APS), and a Berner low-pressure Impactor (BLPI) collected size-segregated aerosol samples for subsequent elemental analysis. A laser diffraction particle size analyzer (Beckman Coulter LS230) was used to determine the size distributions of ash deposit samples. Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS) was used to determine the morphology and composition of ash deposit samples. For the pilot-scale tests reported here, the experimental results suggested little difference in mineral matter behavior between pure coal and biomass blends. The measured aerosol PSDs showed nearly identical behaviors, with modes at approximately 20 nm and 3 μm. The size-segregated aerosol particles were slightly enriched in Na, K, and Ca and deficient in Si and Al for biomass blends compared to the pure coal. The deposition rates were 60% greater in port 7 than in port 10 at 106 vs 65 g/(m2 h). Deposit samples collected for 90 min showed essentially the same deposition rate for coal and the two biomass blends, while short deposition times (30 min) suggested higher initial deposition rates for the biomass blends. The deposit composition and morphology were nearly identical for all three fuels.

Revisiting matrix-based inversion of scanning mobility particle sizer (SMPS) and humidified tandem differential mobility analyzer (HTDMA) data

Abstract. Tikhonov regularization is a tool for reducing noise amplification during data inversion. This work introduces RegularizationTools.jl, a general-purpose software package for applying Tikhonov regularization to data. The package implements well-established numerical algorithms and is suitable for systems of up to ∼ 1000 equations. Included is an abstraction to systematically categorize specific inversion configurations and their associated hyperparameters. A generic interface translates arbitrary linear forward models defined by a computer function into the corresponding design matrix. This obviates the need to explicitly write out and discretize the Fredholm integral equation, thus facilitating fast prototyping of new regularization schemes associated with measurement techniques. Example applications include the inversion involving data from scanning mobility particle sizers (SMPSs) and humidified tandem differential mobility analyzers (HTDMAs). Inversion of SMPS size distributions reported in this work builds upon the freely available software DifferentialMobilityAnalyzers.jl. The speed of inversion is improved by a factor of ∼ 200, now requiring between 2 and 5 ms per SMPS scan when using 120 size bins. Previously reported occasional failure to converge to a valid solution is reduced by switching from the L-curve method to generalized cross-validation as the metric to search for the optimal regularization parameter. Higher-order inversions resulting in smooth, denoised reconstructions of size distributions are now included in DifferentialMobilityAnalyzers.jl. This work also demonstrates that an SMPS-style matrix-based inversion can be applied to find the growth factor frequency distribution from raw HTDMA data while also accounting for multiply charged particles. The outcome of the aerosol-related inversion methods is showcased by inverting multi-week SMPS and HTDMA datasets from ground-based observations, including SMPS data obtained at Bodega Marine Laboratory during the CalWater 2/ACAPEX campaign and co-located SMPS and HTDMA data collected at the US Department of Energy observatory located at the Southern Great Plains site in Oklahoma, USA. Results show that the proposed approaches are suitable for unsupervised, nonparametric inversion of large-scale datasets as well as inversion in real time during data acquisition on low-cost reduced-instruction-set architectures used in single-board computers. The included software implementation of Tikhonov regularization is freely available, general, and domain-independent and thus can be applied to many other inverse problems arising in atmospheric measurement techniques and beyond.

Evolution of size-segregated aerosol concentration in NW Spain: A two-step classification to identify new particle formation events

Real-time measurements of particles in the 15–736 nm range have been obtained by a Scanning Mobility Particle Sizer to characterize the evolution of particle size distribution and new particle formation (NPF) events in an urban background area. The annual, weekly and diurnal variations of the modal (nucleation (Nnuc), Aitken (NAit) and accumulation (Nacc)) particle concentrations were characterised. The NAit and Nacc registered their maximums in cold months during rush hours, in the morning (0600–0900 UTC) and in the afternoon (1700–2000 UTC), while the maximums for Nnuc were reached in warm months during midday hours. NAit, Nacc and Ntotal showed a significant negative correlation with wind speed and a different relationship with the planetary boundary layer (PBL) height by periods. In the warm period, a positive significant correlation between PBL and Nnuc was registered, indicating that the higher dispersion promoted by a high PBL causes favourable conditions for the occurrence of NPF events (a low polluted atmosphere). NPF processes are one of the main sources of ultrafine particles (<100 nm) in the warm period. After a visual-based classification, 45 NPF events of type Ia (strong and with a good confidence level) were identified and analysed, occurring primarily between 1100 and 1500 UTC, mainly in spring and summer. In addition, a two-step method was developed for identifying NPF events: cluster analysis followed by discriminant analysis. The application of discriminant analysis to one of the clusters, grouping 93 days, enabled us to identify 55 of the 56 NPF events days included in the cluster. This method is a valuable tool for identifying NPF events quickly and effectively.

How weather events modify aerosol particle size distributions in the Amazon boundary layer

Abstract. This study evaluates the effect of weather events on the aerosol particle size distribution (PSD) at the Amazon Tall Tower Observatory (ATTO). This research combines in situ measurements of PSD and remote sensing data of lightning density, brightness temperature, cloud top height, cloud liquid water, and rain rate and vertical velocity. Measurements were obtained by scanning mobility particle sizers (SMPSs), the new generation of GOES satellites (GOES-16), the SIPAM S-band radar and the LAP 3000 radar wind profiler recently installed at the ATTO-Campina site. The combined data allow exploring changes in PSD due to different meteorological processes. The average diurnal cycle shows a higher abundance of ultrafine particles (NUFP) in the early morning, which is coupled with relatively lower concentrations in Aitken (NAIT) and accumulation (NACC) mode particles. From the early morning to the middle of the afternoon, an inverse behavior is observed, where NUFP decreases and NAIT and NACC increase, reflecting a typical particle growth process. Composite figures show an increase of NUFP before, during and after lightning was detected by the satellite above ATTO. These findings strongly indicate a close relationship between vertical transport and deep convective clouds. Lightning density is connected to a large increase in NUFP, beginning approximately 100 min before the maximum lightning density and reaching peak values around 200 min later. In addition, the removal of NACC by convective transport was found. Both the increase in NUFP and the decrease in NACC appear in parallel with the increasing intensity of lightning activity. The NUFP increases exponentially with the thunderstorm intensity. In contrast, NAIT and NACC show a different behavior, decreasing from approximately 100 min before the maximum lightning activity and reaching a minimum at the time of maximum lightning activity. The effect of cloud top height, cloud liquid water and rain rate shows the same behavior, but with different patterns between seasons. The convective processes do not occur continually but are probably modulated by gravity waves in the range of 1 to 5 h, creating a complex mechanism of interaction with a succession of updrafts and downdrafts, clouds, and clear-sky situations. The radar wind profiler measured the vertical distribution of the vertical velocity. These profiles show that downdrafts are mainly located below 10 km, while aircraft observations during the ACRIDICON–CHUVA campaign had shown maximum concentrations of ultrafine particles mainly above 10 km. Our study opens new scientific questions to be evaluated in order to understand the intricate physical and chemical mechanisms involved in the production of new particles in Amazonia.

Evolution under dark conditions of particles from old and modern diesel vehicles in a new environmental chamber characterized with fresh exhaust emissions

Abstract. Atmospheric particles have several impacts on health and the environment, especially in urban areas. Parts of those particles are not fresh and have undergone atmospheric chemical and physical processes. Due to a lack of representativeness of experimental conditions and experimental artifacts such as particle wall losses in chambers, there are uncertainties on the effects of physical processes (condensation, nucleation and coagulation) and their role in particle evolution from modern vehicles. This study develops a new method to correct wall losses, accounting for size dependence and experiment-to-experiment variations. It is applied to the evolution of fresh diesel exhaust particles to characterize the physical processes which they undergo. The correction method is based on the black carbon decay and a size-dependent coefficient to correct particle distributions. Six diesel passenger cars, Euro 3 to Euro 6, were driven on a chassis dynamometer with Artemis Urban cold start and Artemis Motorway cycles. Exhaust was injected in an 8 m3 chamber with Teflon walls. The physical evolution of particles was characterized during 6 to 10 h. Increase in particle mass is observed even without photochemical reactions due to the presence of intermediate-volatility organic compounds and semi-volatile organic compounds. These compounds were quantified at emission and induce a particle mass increase up to 17 % h−1, mainly for the older vehicles (Euro 3 and Euro 4). Condensation is 4 times faster when the available particle surface is multiplied by 6.5. If initial particle number concentration is below [8–9] × 104 cm−3, a nucleation mode seems to be present but not measured by a scanning mobility particle sizer (SMPS). The growth of nucleation-mode particles results in an increase in measured [PN]. Above this threshold, particle number concentration decreases due to coagulation, up to −27 % h−1. Under those conditions, the chamber and experimental setup are well suited to characterizing and quantifying the process of coagulation.

IVOC/SVOC and size distribution characteristics of particulate matter emissions from a modern aero-engine combustor in different operational modes

The particulate matter (PM) of Intermediate-Volatile Organic Compounds (IVOC) / Semi-Volatile Organic Compound (SVOC) from aircraft engine emissions, despite being significant precursors of secondary organic aerosols deteriorating air quality in the vicinity of airports, have not been fully investigated at molecular level. In this study, the particulate IVOC/SVOC emissions from a rig test on a Technology of Low Emission Stirred Swirl aero-engine combustor, being operated with dual diffusion and premixed-dominant combustion modes, have been characterized via a two-dimensional gas chromatography-time of flight mass spectrometer (GC × GC-ToFMS). The IVOC/SVOC compounds, including 25n-alkanes, 15 cyclic alkanes and 13 polycyclic aromatic hydrocarbons were analyzed in this study. We found that including the premixed-dominant combustion mode at climb/takeoff conditions reduced the particulate IVOC/SVOC emissions significantly by nearly 80%, compared to using the diffusion combustion mode alone at idle/approach condition. Meanwhile, the measurements on organic PM obtained from a scanning mobility particle sizer spectrometer with a catalytic stripper demonstrated a consistent trend with the the IVOC/SVOC emissions, which were also suppressed by over 85% at climb/takeoff compared to idle/approach. The inter-relationship between the size-resolved organic PM and the speciated IVOC/SVOC emissions has been further explored, showing that the nucleation mode PM is dominated in organic PM by over 50%, in which IVOCs/SVOCs may be a significant contributor. This study expands the understanding of aviation-emitted organic particles, and suggests a path for future aero-engine development to mitigate the IVOC/SVOC emissions particularly at low power conditions. However, compared to the real aero-engine emissions, the results from rig combustor tests should be interpreted with great care, since there are still some work to be done to establish the quantitative relationship between emissions from rig combustors andthose from real engines.

Exposure assessment of nanotitanium oxide powder handling using real-time size-selective particle number concentration measurements and X-ray fluorescence spectrometry -The possibility of exposure to nonagglomerated nanomaterials during the handling of nanomaterial fine powders.

In this study, airborne particles were collected using filters, and the particle number concentrations were measured in two nanotitanium dioxide (nanoTiO2)-manufacturing plants. Real-time particle size measurements were performed using both optical and scanning mobility particle sizer and X-ray fluorescence spectrometry (XRF). The respirable particles collected using filters were used to analyze Ti concentrations in the workplace air of two factories engaged in nanoTiO2 powder bagging processes. The XRF analysis revealed sufficient sensitivity to measure 0.03 mg/m3, which is 1/10 the concentration of the recommended occupational exposure limit of nanoTiO2 in both stationary sampling and personal exposure sampling settings. In a factory where outside air was directly introduced, micron-sized aggregated particles were generated because of factory operations; however, nanosized and submicron-sized particles were not observed owing to high background concentrations of incidental nanoparticles. Alternatively, in another factory where particles from the outside air were removed using a high-efficiency particulate air filter, work-related nanoparticles were released. The findings of this study suggest that in nanoparticle powder handling processes, a nanoparticle exposure risk exists in the form of nonagglomerated state in nanoparticle powder handling processes.

Chemical Emissions from Cured and Uncured 3D-Printed Ventilator Patient Circuit Medical Parts.

Medical shortages during the COVID-19 pandemic saw numerous efforts to 3D print personal protective equipment and treatment supplies. There is, however, little research on the potential biocompatibility of 3D-printed parts using typical polymeric resins as pertaining to volatile organic compounds (VOCs), which have specific relevance for respiratory circuit equipment. Here, we measured VOCs emitted from freshly printed stereolithography (SLA) replacement medical parts using proton transfer reaction mass spectrometry and infrared differential absorption spectroscopy, and particulates using a scanning mobility particle sizer. We observed emission factors for individual VOCs ranging from ∼0.001 to ∼10 ng cm–3 min–1. Emissions were heavily dependent on postprint curing and mildly dependent on the type of SLA resin. Curing reduced the emission of all observed chemicals, and no compounds exceeded the recommended dose of 360 μg/d. VOC emissions steadily decreased for all parts over time, with an average e-folding time scale (time to decrease to 1/e of the starting value) of 2.6 ± 0.9 h.

Effect of Oil Properties on the Generation of Nano-Aerosols During Bubble Bursting Through Crude Oil-Dispersant Slicks.

This study examines the effect of dispersant and oil properties on the aerosolization of fresh and weathered surface crude oil slicks by bursting of a plume of ∼0.7 mm bubbles. A scanning mobility particle sizer measures the size distribution of aerosols in the 20-400 nm range in a clean air chamber. The 500-μm-thick slicks contain oils with varying origin, viscosity, interfacial tension, and weathering state. Test are performed with and without premixed dispersant (Corexit 9500A), which reduces the oil-seawater interfacial tension by 2 orders of magnitude at a dispersant-to-oil ratio (DOR) of 1:25. When compared to aerosolization in clean seawater, the nano-aerosol concentration decreases for slicks without dispersant but increases by 27%-351% upon introduction of dispersant. For most cases, the airborne nanodroplet concentration increases with decreasing Capillary or Morton numbers as well as the ratio of the so-called inner to thermal length scales. To explain the airborne nanodroplet generation in an oil-dispersant mixture, we show that prior to bubble injection, even minimal agitation of the interface causes generation of a subsurface cloud of nanodroplets that diffuses away from the interface. This process appears to be caused by thermal capillary instability when the interfacial tension is low enough to increase the thermal length scale to a few nanometers.

Physical and chemical properties of black carbon and organic matter from different combustion and photochemical sources using aerodynamic aerosol classification

Abstract. The physical and chemical properties of black carbon (BC) and organic aerosols are important for predicting their radiative forcing in the atmosphere. During the Soot Aerodynamic Size Selection for Optical properties (SASSO) project and a EUROCHAMP-2020 transnational access project, different types of light-absorbing carbon were studied, including BC from catalytically stripped diesel exhaust, an inverted flame burner, a colloidal graphite standard (Aquadag) and controlled flaming wood combustion. Brown carbon (BrC) was also investigated in the form of organic aerosol emissions from wood burning (pyrolysis and smouldering) and from the nitration of secondary organic aerosol (SOA) proxies produced in a photochemical reaction chamber. Here we present insights into the physical and chemical properties of the aerosols, with optical properties presented in subsequent publications. The dynamic shape factor (χ) of BC particles and material density (ρm) of organic aerosols was investigated by coupling a charging-free Aerodynamic Aerosol Classifier (AAC) with a Centrifugal Particle Mass Analyzer (CPMA) and a Scanning Mobility Particle Sizer (SMPS). The morphology of BC particles was captured by transmission electron microscopy (TEM). For BC particles from the diesel engine and flame burner emissions, the primary spherule sizes were similar, around 20 nm. With increasing particle size, BC particles adopted more collapsed/compacted morphologies for the former source but tended to show more aggregated morphologies for the latter source. For particles emitted from the combustion of dry wood samples, the χ of BC particles and the ρm of organic aerosols were observed in the ranges 1.8–2.17 and 1.22–1.32 g cm−3, respectively. Similarly, for wet wood samples, the χ and ρm ranges were 1.2–1.85 and 1.44–1.60 g cm−3, respectively. Aerosol mass spectrometry measurements show no clear difference in mass spectra of the organic aerosols in individual burn phases (pyrolysis or smouldering phase) with the moisture content of the wood samples. This suggests that the effect moisture has on the organic chemical profile of wood burning emissions is through changing the durations of the different phases of the burn cycle, not through the chemical modification of the individual phases. In this study, the incandescence signal of a Single Particle Soot Photometer (SP2) was calibrated with three different types of BC particles and compared with that from an Aquadag standard that is commonly used to calibrate SP2 incandescence to a BC mass. A correction factor is defined as the ratio of the incandescence signal from an alternative BC source to that from the Aquadag standard and took values of 0.821 ± 0.002 (or 0.794 ± 0.005), 0.879 ± 0.003 and 0.843 ± 0.028 to 0.913 ± 0.009 for the BC particles emitted from the diesel engine running under hot (or cold idle) conditions, the flame burner and wood combustion, respectively. These correction factors account for differences in instrument response to BC from different sources compared to the standardised Aquadag calibration and are more appropriate than the common value of 0.75 recommended by Laborde et al. (2012b) when deriving the mass concentration of BC emitted from diesel engines. Quantifying the correction factor for many types of BC particles found commonly in the atmosphere may enable better constraints to be placed on this factor depending on the BC source being sampled and thus improve the accuracy of future SP2 measurements of BC mass concentrations.

Uniform deposition method of monodispersed SiO2 nanoparticles on a 300-mm Si wafer surface.

A study of the uniform deposition of nanoparticles across a 300-mm wafer was conducted to assess the uniformity of the wafer center-to-edge cleaning technique. A new method of particle deposition was devised different from the conventional method using electrostatic force. The strategy implements wafer rotation and deposition through principles of convection and diffusion. In this study, we focused on the effect of wafer rotation speed on particle deposition. After determining optimum conditions, fine results were obtained with a well-deposited shape and an excellent particle size uniformity of above 70% over the entire area of the wafer except in unusual cases. Deposition results were confirmed with KLA-Tencor Surfscan SP5 commonly used by foundries, and logic and memory manufacturers around the world to increase node development and production. The inherent indexof the refraction value by Surfscan SP5 caused a particle size shift in measurement results. However, scanning electron microscopy and scanning mobility particle sizer analysis results revealed that 80-, 60-, 40-, 30-, and 20-nm-sized silica nanoparticles were well deposited on the wafer. Through this research, we believe that standard wafers processed with this particle deposition method will be useful for performance evaluation of wafer cleaning technology and calibration of wafer inspection technology during development.

Formation and evolution of secondary organic aerosols derived from urban-lifestyle sources: vehicle exhaust and cooking emissions

Abstract. Vehicle exhaust and cooking emissions are closely related to the daily life of city dwellers. Here, we defined the secondary organic aerosols (SOAs) derived from vehicle exhaust and cooking emissions as “urban-lifestyle SOAs” and simulated their formation using a Gothenburg potential aerosol mass reactor (Go:PAM). The vehicle exhaust and cooking emissions were separately simulated, and their samples were defined as “vehicle group” and “cooking group”, respectively. After samples had been aged under 0.3–5.5 d of equivalent photochemical age, these two urban-lifestyle SOAs showed markedly distinct features in the SOA mass growth potential, oxidation pathways, and mass spectra. The SOA/POA (primary organic aerosol) mass ratios of vehicle groups (107) were 44 times larger than those of cooking groups (2.38) at about 2 d of equivalent photochemical age, according to the measurement of scanning mobility particle sizer (SMPS). A high-resolution time-of-flight aerosol mass spectrometer was used to perform a deeper analysis. It revealed that organics from the vehicle may undergo the alcohol and/or peroxide and carboxylic acid oxidation pathway to produce abundant less and more oxidized oxygenated OAs (LO-OOAs and MO-OOAs), and only a few primary hydrocarbon-like organic aerosols (HOAs) remain unaged. In contrast, organics from cooking may undergo the alcohol and/or peroxide oxidation pathway to produce moderate LO-OOAs, and comparable primary cooking organic aerosols (COAs) remain unaged. Our findings provide an insight into atmospheric contributions and chemical evolutions for urban-lifestyle SOAs, which could greatly influence the air quality and health risk assessments in urban areas.

Physical and chemical characterization of two kinds of coal-derived soot

The chemical composition, oxidation reactivity, nanostructure, and particle size of two coal-derived soot were experimentally investigated. The soot samples were collected from Yinni (YN) and Datong (DT) single coal combustion flames through a nitrogen-quenched sampling tube. The collected soot samples were then tested on an X-ray photoelectron spectroscopy (XPS) and a thermogravimetric analyzer (TGA) to obtain their surface chemistry and oxidation reactivity. XPS analysis showed that extensive C and O, as well as trace other elements, including S, Na, Fe, and Si, etc., appeared on the surface of the two coal-derived soot. The sp2/sp3 content of YN soot was higher than that of DT soot, indicating the better reactivity of YN soot. The results of TGA experiments showed that the oxidation reaction constant of YN soot was indeed larger than DT soot. Interestingly, the two coal-derived soot contained a portion of unburned ash after the TGA oxidation experiments.The nanostructure and particle size distribution function of soot generated in YN and DT single coal combustion flames were also studied by a self-designed thermophoresis sampling system combined with scanning electron microscopy (SEM) and an online dilution probe in conjunction with scanning mobility particle sizer (SMPS). From the SEM images collected from a relatively low height of the single coal flames, a small-sized individual nascent soot and a large-sized and liquid-like drops were observed. With the increase of flame height, the primary particle size of the two kinds of coal-derived soot aggregates decreased due to oxidation, while the primary particle number increased because of agglomeration. The soot aggregates sampled from higher heights of the two single coal flames had a relatively larger particle size but lower concentration.

Characterizing the performance of a POPS miniaturized optical particle counter when operated on a quadcopter drone

Abstract. We first validate the performance of the Portable Optical Particle Spectrometer (POPS), a small light-weight and high sensitivity optical particle counter, against a reference scanning mobility particle sizer (SMPS) for a month-long deployment in an environment dominated by biomass burning aerosols. Subsequently, we examine any biases introduced by operating the POPS on a quadcopter drone, a DJI Matrice 200 V2. We report the root mean square difference (RMSD) and mean absolute difference (MAD) in particle number concentrations (PNCs) when mounted on the UAV and operating on the ground and when hovering at 10 m. When wind speeds are low (less than 2.6 m s−1), we find only modest differences in the RMSDs and MADs of 5 % and 3 % when operating at 10 m altitude. When wind speeds are between 2.6 and 7.7 m s−1 the RMSDs and MADs increase to 26.2 % and 19.1 %, respectively, when operating at 10 m altitude. No statistical difference in PNCs was detected when operating on the UAV in either ascent or descent. We also find size distributions of aerosols in the accumulation mode (defined by diameter, d, where 0.1 ≤ d ≤ 1 µm) are relatively consistent between measurements at the surface and measurements at 10 m altitude, while differences in the coarse mode (here defined by d &gt; 1 µm) are universally larger. Our results suggest that the impact of the UAV rotors on the POPS PNCs are small at low wind speeds, but when operating under a higher wind speed of up to 7.6 m s−1, larger discrepancies occur. In addition, it appears that the POPS measures sub-micron aerosol particles more accurately than super-micron aerosol particles when airborne on the UAV. These measurements lay the foundations for determining the magnitude of potential errors that might be introduced into measured aerosol particle size distributions and concentrations owing to the turbulence created by the rotors on the UAV.