Scanning Mobility Particle Sizer Data Research Articles

Analytical deconvolution of smearing effect for inversion of scanning mobility particle sizer data

The scanning mobility particle sizer (SMPS) is a key instrument for aerosol studies that enables rapid measurement of particle size distribution. When SMPS data are inverted, the smearing effect needs to be considered. Previous studies used numerical methods to deconvolute the smearing effect. In this paper, to reduce the complexity of SMPS data inversion, we derive an analytical formula for de-smearing, and include our de-smearing formula into a full SMPS data inversion scheme. We also propose the voltage step change experiment to characterize the smearing effect of an SMPS. The effectiveness and robustness of our de-smearing approach were demonstrated using experimental data.

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.

Investigation of physico-chemical characteristics and associated CCN activation for different combustion sources through Chamber experiment approach

The aerosol physico-chemical properties along with their CCN activation characteristics were studied for different combustion source types such as Diesel Generator (DG), wood, leaf, charcoal, grass and cow dung through chamber-based experiment. Aethalometer (AE-33), High resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS), scanning mobility particle sizer (SMPS) and cloud condensation nuclei (CCN) counter were connected in line to derive the absorption properties, chemical composition, size distribution and CCN number concentrations respectively. Angstrom absorption exponent (AAE) and Angstrom absorption exponent ratio (AAER) were estimated utilizing the Aethalometer data. The analysis reveals that the DG emission was associated with the lowest AAE value (0.92) and the AAE value was highest for cow dung emissions (2.15). AAER, a ratio of AAE at longer wavelengths (660–950 nm) to smaller wavelengths (370-660 nm), showed value < 1 for most of biomass burning types, whereas, the AAER value was >1 for DG emission. The chemical composition data reveals that the organics contribute more than 90% to most of the combustion sources except charcoal, for which the organic contribution was only 78%. High-resolution data analysis reveals that leaf burning was associated with the highest f44 fraction indicating the emitted organic aerosols contain more oxygen. The chemical composition derived hygroscopicity parameter (κ) was estimated to be highest for charcoal emissions and lowest for diesel and cooking emissions. Hygroscopicity parameter (κ) was also evaluated utilizing CCN and SMPS data. The CCN activation and size distribution analysis revealed that the CCN activation of cow dung was highest at 0.1% and 0.3% SS, this is associated with the higher geometric mean diameter (GMD) of emitted aerosols, indicating the importance of size compared to the chemical composition. The activation fraction of charcoal emission was found to be higher than DG emission in these super-saturations, indicating the importance of hygroscopicity in addition to size for governing the CCN activation when the GMD is on the lower side.

Quantification of Non-refractory Aerosol Nitrate in Ambient Air by Thermal Dissociation Cavity Ring-Down Spectroscopy.

A thermal dissociation cavity ring-down spectrometer (TD-CRDS) for real-time quantification of non-refractory aerosol nitrate in ambient air is described. The instrument uses four parallel detection channels and heated quartz inlets to convert particulate organic nitrate (pON) (at 350 °C) and ammonium nitrate (NH4NO3) aerosol (at 540 °C) to nitrogen dioxide (NO2), whose mixing ratio is monitored via its absorption at 405 nm. Concentrations of aerosol nitrate are determined by difference relative to a parallel TD-CRDS channel in which aerosol is removed by in-line filtering. The method was validated by sampling gas streams containing laboratory-generated NH4NO3 aerosol in parallel to a scanning mobility particle sizer (SMPS). Scatter plots of TD-CRDS and SMPS data correlated (r2 > 0.9) with slopes near unity, confirming quantitative TD-CRDS response to NH4NO3 aerosol. In contrast, no response was observed when sampling (NH4)2SO4 aerosol. Instrument limits of detection (LOD; 2σ, 10 s) were 120 parts per trillion by volume (10-12, pptv) for NO2 and 148 pptv for ammonium nitrate. Partial and unsustained conversion of refractory sodium nitrate (NaNO3) was observed at the inlet temperature used for complete dissociation of HNO3 and NH4NO3, suggesting that this channel may not constitute a robust measurement of total odd nitrogen (NOy) in environments where NaNO3 particles may be present (e.g., the polluted marine boundary layer). A potential application of the TD-CRDS is the calibration of particle counters, for which convenient methods are not currently available. Sample ambient air measurements of pON and total aerosol nitrate in Calgary are presented.

Emissions of Secondary Formed ZnO Nano-Objects from the Combustion of Impregnated Wood. An Online Size-Resolved Elemental Investigation

The release of secondary nano-objects formed during waste combustion processes is becoming a matter of concern, considering their known toxicity and the fact that the 100% efficiency of filtering systems is not always ensured. An increased cytotoxicity and genotoxicity on human peripheral blood lymphocytes is known particularly in the case of ZnO, which is often contained in paints and waterproof agents, heading to a relevant quantity present in the waste wood material. In this study, the behavior of ZnO nanoparticles during wood combustion and the effect of the reduction potential of generated carbon species on the release of secondarily formed ZnO-containing nano-objects were investigated. By hyphenating a modified scanning mobility particle sizer (SMPS) and inductively coupled mass spectrometry (ICP-MS), it was possible to obtain simultaneously size-resolved and chemical information on the emitted nanoparticles. Through the established correlation between SMPS and ICP-MS signals, Zn-containing particles were efficiently resolved from the combustion generated particles. Transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) on size-selected particles confirmed the SMPS and ICP-MS data. The use of electron diffraction allowed determining the structure of the crystalline materials as hexagonal ZnO. A possible mechanism of reduction of ZnO to Zn and further reformation as secondary nano-objects is proposed.

Design and Performance Evaluation of a PN1 Sensor for Real-Time Measurement of Indoor Aerosol Size Distribution

Airborne particulate matter is an important factor in the quality of an indoor environment. In this study, a miniaturized particle sensor was developed to detect submicron-sized aerosols based on number counting. This particle number (PN) sensor was designed and fabricated for real-time measurement of total aerosol number concentration and geometric mean diameter. The sensor (hereafter called as PN1 sensor) comprised a particle-classification unit, a particle-charging unit, and a particle-detection unit. After integrating all the three units, the total number concentration and the geometric mean diameter of test aerosol particles were determined and the results were compared with those obtained using commercial instruments. First, the PN1 sensor was compared with a condensation particle counter (CPC) in lab-test. For this, different groups of monodisperse sodium chloride particles between 20 and 700 nm in diameter were used. Then the PN1 sensor was compared with a scanning mobility particle sizer (SMPS) and an aerodynamic particle sizer (APS). For this, the PN1 sensor data were obtained by varying the combination of two corona voltage and test particles (sodium chloride and polystyrene latex) size distribution. In addition to lab-test, field test was carried out with indoor aerosols in different places. The number concentration and geometric mean diameter of indoor aerosols were measured by PN1 sensor and compared with SMPS data. The number concentration was also compared with the results of CPC and Pegasor AQ Indoor (Pegasor, Finland) measurements.

Assessment of personal exposure to airborne nanomaterials: Evaluation of a novel sampler

A novel sampler, the NANOBADGE, has been developed to assess personal exposure to nano-objects, agglomerates and aggregates (NOAA) at the workplace. The NANOBADGE collects particles on filters subsequently analyzed by X-Ray Fluorescence spectroscopy (XRF), which provides a mass-based quantification with chemical selectivity. The NANOBADGE was benchmarked against a scanning mobility particle sizer (SMPS) and a DiSCmini by carrying out simultaneous measurements on test aerosols of ZnO or TiO2 for particle sizes between 20 and 400 nm for which the DiSCmini has its highest accuracy. The effective density and shape of the NOAA present in the test aerosols were determined experimentally to compare number-based data obtained with the SMPS and the DiSCmini with mass-based data obtained with the NANOBADGE. The agreement between the SMPS and the NANOBADGE sampler was within ± 25 % on all test aerosols. The converted DiSCmini data matched the SMPS and sampler data for polydisperse aerosols in the specified size range as long as the DiSCmini assumptions meet the aerosol characteristics (i.e. lognormal size distribution with a given geometric standard deviation σg = 1.9). The detection limits of the NANOBADGE sampler were in the order of tens of nanograms per filter, which is low enough to reliably detect exposure levels below the recommended exposure limit (REL) of the National Institute for Occupational Safety and Health (NIOSH) and the Institut National de Recherche et de Sécurité (INRS) for ultrafine ZnO and TiO2 even for short-term exposure situations.

Understanding aerosol formation mechanisms in a subtropical atmosphere impacted by biomass burning and agroindustry

This work provides evidence for the existence of strong seasonality in homogeneous and heterogeneous aerosol formation in a subtropical region affected by agricultural biomass burning. Acquisitions of aerosol size distributions were made in central São Paulo State between August 2011 and November 2012, using a scanning mobility particle sizer (SMPS) system. Aerosols were also collected using a high volume impactor for analysis of major ions in the <0.49μm size fraction. The SMPS data were grouped into three size fractions: <25nm, 25–100nm, and 100–615nm, which were used to represent the nucleation, Aitken, and lower accumulation mode size ranges, respectively. Different aerosol types and atmospheric conditions were shown to influence the relative contributions of the different aerosol size fractions and their interrelationships. The total number concentrations of particles in the nucleation size range varied between 4.03×10−3 and 5.18×104cm−3, concentrations in the Aitken size range varied between 1.60×101 and 3.17×104cm−3, and concentrations in the accumulation size range varied between 0.00 and 6.67×103cm−3. Distinct seasonal differences in particle formation were observed, with evidence for the preferential occurrence of homogeneous nucleation during the wetter summer months and heterogeneous nucleation during the winter when there were strong emissions from biomass burning. Homogeneous nucleation of new particles was inhibited in the winter, due to the greater surface area of existing aerosols available for the uptake of reactive gases. Consequently, the nucleation and Aitken modes were favored in the wet (summer) and dry (winter biomass burning) periods, respectively. The accumulation mode showed peaks in the summer and winter, which could be explained by hygroscopic particle growth and heterogeneous reactions, respectively.

Comparison of data analysis procedures for real-time nanoparticle sampling data using classical regression and ARIMA models

ABSTRACTReal-time monitoring is necessary for nanoparticle exposure assessment to characterize the exposure profile, but the data produced are autocorrelated. This study was conducted to compare three statistical methods used to analyze data, which constitute autocorrelated time series, and to investigate the effect of averaging time on the reduction of the autocorrelation using field data. First-order autoregressive (AR(1)) and autoregressive-integrated moving average (ARIMA) models are alternative methods that remove autocorrelation. The classical regression method was compared with AR(1) and ARIMA. Three data sets were used. Scanning mobility particle sizer data were used. We compared the results of regression, AR(1), and ARIMA with averaging times of 1, 5, and 10 min. AR(1) and ARIMA models had similar capacities to adjust autocorrelation of real-time data. Because of the non-stationary of real-time monitoring data, the ARIMA was more appropriate. When using the AR(1), transformation into stationary data was necessary. There was no difference with a longer averaging time. This study suggests that the ARIMA model could be used to process real-time monitoring data especially for non-stationary data, and averaging time setting is flexible depending on the data interval required to capture the effects of processes for occupational and environmental nano measurements.

Aerosol effective density measurement using scanning mobility particle sizer and quartz crystal microbalance with the estimation of involved uncertainty

Abstract. In this work, we have used a scanning mobility particle sizer (SMPS) and a quartz crystal microbalance (QCM) to estimate the effective density of aerosol particles. This approach is tested for aerosolized particles generated from the solution of standard materials of known density, i.e. ammonium sulfate (AS), ammonium nitrate (AN) and sodium chloride (SC), and also applied for ambient measurement in New Delhi. We also discuss uncertainty involved in the measurement. In this method, dried particles are introduced in to a differential mobility analyser (DMA), where size segregation is done based on particle electrical mobility. Downstream of the DMA, the aerosol stream is subdivided into two parts. One is sent to a condensation particle counter (CPC) to measure particle number concentration, whereas the other one is sent to the QCM to measure the particle mass concentration simultaneously. Based on particle volume derived from size distribution data of the SMPS and mass concentration data obtained from the QCM, the mean effective density (ρeff) with uncertainty of inorganic salt particles (for particle count mean diameter (CMD) over a size range 10–478 nm), i.e. AS, SC and AN, is estimated to be 1.76 ± 0.24, 2.08 ± 0.19 and 1.69 ± 0.28 g cm−3, values which are comparable with the material density (ρ) values, 1.77, 2.17 and 1.72 g cm−3, respectively. Using this technique, the percentage contribution of error in the measurement of effective density is calculated to be in the range of 9–17 %. Among the individual uncertainty components, repeatability of particle mass obtained by the QCM, the QCM crystal frequency, CPC counting efficiency, and the equivalence of CPC- and QCM-derived volume are the major contributors to the expanded uncertainty (at k = 2) in comparison to other components, e.g. diffusion correction, charge correction, etc. Effective density for ambient particles at the beginning of the winter period in New Delhi was measured to be 1.28 ± 0.12 g cm−3. It was found that in general, mid-day effective density of ambient aerosols increases with increase in CMD of particle size measurement but particle photochemistry is an important factor to govern this trend. It is further observed that the CMD has good correlation with O3, SO2 and ambient RH, suggesting that possibly sulfate secondary materials have a substantial contribution in particle effective density. This approach can be useful for real-time measurement of effective density of both laboratory-generated and ambient aerosol particles, which is very important for studying the physico-chemical properties of particles.

A Novel Porous Tube Reactor for Nanoparticle Synthesis with Simultaneous Gas-Phase Reaction and Dilution

A novel porous tube reactor that combines simultaneous reactions and continuous dilution in a single-stage gas-phase process was designed for nanoparticle synthesis. The design is based on the atmospheric pressure chemical vapor synthesis (APCVS) method. In comparison to the conventional hot wall chemical vapor synthesis reactor, the APCVS method offers an effective process for the synthesis of ultrafine metal particles with controlled oxidation. In this study, magnetic iron and maghemite were synthesized using iron pentacarbonyl as a precursor. Morphology, size, and magnetic properties of the synthesized nanoparticles were determined. The X-ray diffraction results show that the porous tube reactor produced nearly pure iron or maghemite nanoparticles with crystallite sizes of 24 and 29 nm, respectively. According to the scanning mobility particle sizer data, the geometric number mean diameter was 110 nm for iron and 150 nm for the maghemite agglomerates. The saturation magnetization value of iron was 150 ...

Deposition Removal of Monodisperse and Polydisperse Submicron Particles by a Negative Air Ionizer

Indoor particulate matter exposure is one of the main environmental risk factors influencing human health. Previous studies have indicated that the degree of hazards about ultrafine particles was associated with the particle surface area and number concentration. Polydisperse submicron particles (PSPs) contribute most of the indoor aerosol particle number and are usually used for removal testing. However, the behaviors of monodisperse submicron particles (MSPs) are easier to analyze. This study aims to investigate the difference between the deposition removal efficiency of MSP and PSP by the negative air ionizer (NAI) under different settings of freestream air velocity (FAV). The particle-removal experiments were conducted in a stainless steel test chamber under the condition of 50% relative humidity and FAV of 0.56, 1.2 and 2.0 m/s. The NaCl and oleic acid PSPs were generated from a constant output atomizer and the NaCl MSPs (30, 50, 100, 170 and 300 nm) were generated by passing the polydisperse NaCl aerosol through a Differential Mobility Analyzer. The concentration and size distribution of the particles in the chamber were monitored with a Scanning Mobility Particle Sizer (SMPS). The decay constant of particles number concentration, particle removal efficiency (PRE), enhancement factor of deposition rate (EF) and air cleaner effectiveness (ACE) were determined from the SMPS data. The decay constant of particle number concentration increased with the decrease of FAV and decreased with the increase of particle size. Both of the PREs of MSP and PSP were quite high, especially for the smaller particles and under low FAV. The EFs ranged from 4.4 to 115.5 and were proportional to the particle size. In addition, the ACE ranged from 0.57 to 0.96 and increased as the particle size increased. These results give a better understanding of the deposition of 30– 300-nm particles enhanced by the NAI and the influential factors.

A Simplified Approach to Calculate Particle Growth Rate Due to Self-Coagulation, Scavenging and Condensation Using SMPS Measurements during a Particle Growth Event in New Delhi

The scanning mobility particle sizer (SMPS) technique is a widely employed technique to measure the particle number size distribution, and thus calculate the particle total growth rate. However, growth due to individual atmospheric processes needs to be known precisely and accurately to better model the secondary aerosol distribution. In this study, we use simplified analytical formulas to calculate the growth rates due to self-coagulation, coagulation scavenging and condensation processes of particle size distribution (9–425 nm) measured using SMPS. Firstly, total growth rate is determined from the regression fit of SMPS data plotted between the geometric mean diameter (GMD) of particle size (nm) versus time (hour) measured during a particle growth event. The SMPS measurements were conducted during November-December 2011 in New Delhi. The particle growth event days and non-event days were classified according to the protocol discussed elsewhere. Assuming that the particle number size distribution of a growing population can be described by a unimodal distribution and particles are neutral in the population, we calculated the growth rate due to self-coagulation (GRscoag), which is proportional to the total number of particles in the mode and mode peak diameter. Similarly, assuming that particles with mode peak size 25 nm and above act as a coagulation sink and grow due to scavenging of newly formed nucleation range particles (< 12 nm), we calculated the coagulation scavenging growth rate (GRscav) as a time derivative of the mode peak diameter, which is equivalent to the product of particle diameter and its coagulation sink. The condensation growth rate (GRcond) is calculated based on the assumption that total growth rate is the summation of the growth resulting of three physical processes: self-coagulation, coagulation scavenging and condensation. During the study period, three event days were recorded at the measurement site. To explain the growth rate calculation approach, which is presented here in detail, we have taken SMPS data of one event day (November 4, 2011) as an example (two other event days are also briefly discussed). On November 4, the total average growth rate was found to be 15.4 ± 11 nm/h, while the average GRscoag, GRscav and GRcond were calculated to be 3.8 ± 0.4 (with min and max values of 2.9–5.1 nm/h), 8.0 ± 6 (0.6–19.3 nm/h) and 3.6 nm/h, respectively. These growth rates are comparable to those reported for other urban sites around the world using different methods. This approach is simple, and growth by individual processes can be calculated without knowing several other parameters, which include vapor concentration of atmospheric constituents, heterogeneous processes, and complex modeling procedures.

Submicron particle characteristics of atmospheres in a long highway tunnel.

This study used a scanning mobility particle sizer (SMPS) to measure and categorize submicron atmospheric particles in the 14-737-nm size range for ambient and urban roadside air and for air in the Hsuehshan Tunnel (12.9 km), Taiwan. Principal component analysis, traffic flow, and particle size distributions were used to identify the emission characteristics of light-duty vehicles (LDV) with the SMPS data. In the Hsuehshan Tunnel, the particle size from the majority of emissions discharged by LDV is approximately 20-60 nm, and the maximum particle number can reach up to 2.5 × 10(5). In contrast, submicron particle size distribution for urban roadsides is mostly 14-200 nm, and the maximum particle number is approximately 4 × 10(4) with the particle number for most particle sizes being below 1,200. The submicron particle size distribution at the ambient air station was unimodal with a mode sizes at 30-50 nm with the maximum particle number of 3,000.

Simplifying aerosol size distributions modes simultaneously detected at four monitoring sites during SAPUSS

Abstract. The analysis of aerosol size distributions is a useful tool for understanding the sources and the processes influencing particle number concentrations (N) in urban areas. Hence, during the one-month SAPUSS campaign (Solving Aerosol Problems by Using Synergistic Strategies, EU Marie Curie Action) in autumn 2010 in Barcelona (Spain), four SMPSs (Scanning Mobility Particle Sizer) were simultaneously deployed at four monitoring sites: a road side (RSsite), an urban background site located in the city (UBsite), an urban background site located in the nearby hills of the city (Torre Collserola, TCsite) and a regional background site located about 50 km from the Barcelona urban areas (RBsite). The spatial distribution of sites allows study of the aerosol temporal variability as well as the spatial distribution, progressively moving away from urban aerosol sources. In order to interpret the data sets collected, a k-means cluster analysis was performed on the combined SMPS data sets. This resulted in nine clusters describing all aerosol size distributions from the four sites. In summary there were three main categories (with three clusters in each category): "Traffic" (Traffic 1, "Tclus_1" – 8%; Traffic 2, "Tclus_2" – 13%; and Traffic 3, "Tclus_3" – 9%) "Background Pollution" (Urban Background 1, "UBclus_1" – 21%; Regional Background 1, "RBclus_1" – 15%; and Regional Background 2, "RBclus_2" – 18%) and "Special Cases" (Nucleation, "NUclus" – 5%; Regional Nitrate, "NITclus" – 6%; and Mix, "MIXclus" – 5%). As expected, the frequency of traffic clusters (Tclus_1–3) followed the order RSsite, UBsite, TCsite, and RBsite. These showed typical traffic modes mainly distributed at 20–40 nm. The urban background sites (UBsite and TCsite) reflected also as expected urban background number concentrations (average values, N = 1.0 × 104 cm−3 and N = 5.5 × 103 cm−3, respectively, relative to 1.3 × 104 cm−3 seen at RSsite). The cluster describing the urban background pollution (UBclus_1) could be used to monitor the sea breeze circulation towards the regional background study area. Overall, the RBsite was mainly characterised by two different regional background aerosol size distributions: whilst both exhibited low N (2.7 × 103 for RBclus_1 and 2.2 × 103 cm−3 for RBclus_2), RBclus_1 had average PM10 concentrations higher than RBclus_2 (27 vs. 23 μg m−3). As regards the minor aerosol size distribution clusters, the "Nucleation" cluster was observed during daytime, whilst the "Regional Nitrate" was mainly seen at night. The ninth cluster ("Mix") was the least well defined and likely composed of a number of aerosol sources. When correlating averaged values of N, NO2 and PM (particulate mass) for each k-means cluster, a linear correlation between N and NO2 with values progressively increasing from the regional site RBsite to the road site RSsite was found. This points to vehicular traffic as the main source of both N and NO2. By contrast, such an association does not exist for the case of the nucleation cluster, where the highest N is found with low NO2 and PM. Finally, the clustering technique allowed study of the impact of meteorological parameters on the traffic N emissions. This study confirms the shrinking of freshly emitted particles (by about 20% within 1 km in less than 10 min; Dall'Osto et al., 2011a) as particles are transported from the traffic hot spots towards urban background environments. Additionally, for a given well-defined aerosol size distribution (Tclus_2) associated with primary aerosol emissions from road traffic we found that N5–15 nm concentrations can vary up to a factor of eight. Within our measurement range of SMPSs (N15–228 nm) and Condensation Particle Counters (CPCs, N&gt;5 nm), we found that ultrafine particles within the range 5–15 nm in urban areas are the most dynamic, being a complex ensemble of primary evaporating traffic particles, traffic tailpipe new particle formation and non-traffic new particle formation.

Comparison of Measured Particle Lung-Deposited Surface Area Concentrations by an Aerotrak 9000 Using Size Distribution Measurements for a Range of Combustion Aerosols

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 generated 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 (R 2 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 exception of coal combustion particles. Although some dependency on aerosol material exists, the instrument measuring lung-deposited SA demonstrated consistent reliability across a range of concentrations for a range of materials. For optimal results however, applying a correction factor (CF) before taking the instrument to the field is recommended. Copyright 2013 American Association for Aerosol Research

Dynamic variations of ultrafine, fine and coarse particles at the Lu-Lin background site in East Asia

The characteristics of atmospheric ultrafine particles (i.e. <100 nm, nanoparticles or PM0.1), PM2.5 and PM10 were studied at the Lulin Atmospheric Background Station (LABS, 2862 m a.s.l., Taiwan) as part of the 7SEAS/Dongsha campaign. Sampling was conducted in July and August of 2009 and September to November of 2010, during which two 96-h and four 72-h PM samples were taken. Real-time particle size distributions were measured continuously from July to August of 2009 and July to November of 2010. PM0.1, PM2.5 and PM10 were collected by using two MOUDIs (micro-orifice uniform deposit impactor, MSP 110) and a Dichotomous PM10 sampler (Andersen SA-241) while real-time size distributions of particles of 5.5–350 nm in diameter were measured by an SMPS (scanning mobility particle sizer, TSI 3936). Filter samples were analyzed for gravimetric mass and chemical compositions, including organic carbon (OC), element carbon (EC), water-soluble ions and trace elements. Meteorology parameters and gaseous O3 and CO concentrations were also monitored along with the SMPS data for studying particle nucleation, condensation, SOA (secondary organic aerosol) formation and long-range air pollutant transport at the LABS. SMPS data showed that nanoparticle concentrations at the LABS remained relatively stable at low level (∼300–500 #/cm3) during the nighttime (22:00–04:00), increased during daytime, and reached a maximum (∼2000–4000 #/cm3) in the afternoon (12:00–16:00). The NMD (number median diameter) showed an opposite trend with the peak number concentrations observed in the afternoon corresponding to the smallest NMD (20–40 nm). These results indicate the dominance of local sources rather than the transport from other atmospheric air because that the lifetime of nanoparticles was only few minutes. Chemical analysis of filter samples showed that the concentrations of trace elements K and Mn, which serve as biomass burning markers, were elevated in the fine particle fractions during November 9–12th when the air mass passed through South and Southeast Asia prior to reaching the LABS. The concentrations of K and Mn would have been low if the aerosols had local origins The biomass burning derived K was found in all fine particle samples at the LABS suggesting that the free troposphere around Taiwan is frequently impacted by the long-range transport of biomass burning plumes via the westerly winds.

The impact of organic coatings on light scattering by sodium chloride particles

Light scattering by airborne particles plays a major role in visibility degradation and climate change. The composition and structure of particles in air can be complex, so that predictions of light scattering a priori have significant uncertainties. We report here studies of light scattering by NaCl, a model for airborne salt particles from the ocean and alkaline lakes, with and without an organic coating formed from the low volatility products of the reaction of α-pinene with ozone at room temperature at 1 atm in air. Light scattering at 450, 550 and 700 nm was measured using an integrating nephelometer on particles whose size distribution was independently determined using a scanning mobility particle sizer (SMPS). For comparison, polystyrene latex spheres (PSL) of a known size and dioctylphthalate (DOP) particles generated with a narrow size distribution were also studied. The measured values were compared to those calculated using Mie theory. Although excellent agreement between experiment and theory was found for the PSL and DOP particles, there were large discrepancies for a polydisperse NaCl sample. These were traced to errors in the size distribution measurements. Despite the use of 85Kr neutralizers, the Boltzmann charge equilibrium distribution assumption used to derive particle size distributions from SMPS data was shown not to be valid, leading to an overestimate of the concentration of larger particles and their contribution to light scattering. Correcting for this, the combination of experiments and theory show that as salt takes up low volatility organics in the atmosphere and the geometric mean diameter increases, the effect on light scattering may be reasonably approximated from the change in size distribution under conditions where the organic coating is small relative to the core size. However, for a given particle diameter, light scattering decreases as the relative contribution of the organic component increases. Thus, light scattering by salt particles with a specific size distribution will be reduced when organics comprise a significant portion of the particles. This will lessen their impact on the visual range compared to pure salt particles, but also lead to less counterbalancing of the tropospheric warming due to greenhouse gases.

Characteristics of size distributions at urban and rural locations in New York

Abstract. Paired nano- and long-tube Scanning Mobility Particle Sizer (SMPS) systems were operated for four different intensive field campaigns in New York State. Two of these campaigns were at Queens College in New York City, during the summer of 2001 and the winter of 2004. The other field campaigns were at rural sites in New York State. The data with the computed diffusion loss corrections for the sampling lines and the SMPS instruments were examined and the combined SMPS data sets for each campaign were obtained. The diffusion corrections significantly affect total number concentrations, and in New York City, affect the mode structure of the size distributions. The relationship between merged and integrated SMPS total number concentrations with the diffusion loss corrections and the CPC number concentrations yield statistically significant increases (closer to 1) in the slope and correlation coefficient compared to the uncorrected values. The measurements are compared to PM2.5 mass concentrations and ion balance indications of aerosol acidity. Analysis of particle growth rate in comparison to other observations can classify the events and illustrate that urban and rural new particle formation and growth are the result of different causes. Periods of low observed PM2.5 mass, high number concentration, and low median diameter due to small fresh particles are associated with primary emissions for the urban sites; and with particle nucleation and growth for the rural sites. The observations of high PM2.5 mass, lower number concentrations, and higher median diameter are mainly due to an enhancement of photochemical reactions leading to condensation processes in relatively aged air. There are statistically different values for the condensation sink (CS) between urban and rural areas. While there is good association (r2&gt;0.5) between the condensation sink (CS) in the range of 8.35–283.9 nm and PM2.5 mass in the urban areas, there is no discernable association in the rural areas. The average values computed for the CS lie in the range 8.7×10−3–3.5×10−2 s−1.

Real‐Time Measurement of the Size Distribution of Diesel Exhaust Particles using a Portable 4‐stage Electrical Low Pressure Impactor

AbstractFor this study, a 4 stage electrical low pressure impactor was designed to measure the real‐time size distribution of diesel particulate matter (DPM). For the performance evaluation, sodium chloride (NaCl) particles and dioctyl sebacate (DOS) particles were used. After evaluating the collection efficiency of each stage of the impactor, the size distributions of test particles were estimated using electrical current data and their inversion algorithm, and this was found to agree with the results obtained by a scanning mobility particle sizer (SMPS). For measurement of DPM, a common‐rail direct injection (CRDI) diesel engine, for engine speeds of 1,200 rpm and 1,500 rpm at 2.7 kgf·m, was used.Therefore, it was found that the size distribution of the DPM could be easily obtained, with the currents measured by the impactor and the data inversion algorithm, in less than 5 seconds. Furthermore, the effective density of the DPM could be obtained using the calculated results and the SMPS data.