A New Time-of-Flight Aerosol Mass Spectrometer (TOF-AMS)—Instrument Description and First Field Deployment

We report the development and first field deployment of a new version of the Aerosol Mass Spectrometer (AMS), which is capable of measuring non-refractory aerosol mass concentrations, chemically speciated mass distributions and single particle information. The instrument was constructed by interfacing the well-characterized Aerodyne AMS vacuum system, particle focusing, sizing, and evaporation/ionization components, with a compact TOFWERK orthogonal acceleration reflectron time-of-flight mass spectrometer. In this time-of-flight aerosol mass spectrometer (TOF-AMS) aerosol particles are focused by an aerodynamic lens assembly as a narrow beam into the vacuum chamber. Non-refractory particle components flash-vaporize after impaction onto the vaporizer and are ionized by electron impact. The ions are continuously guided into the source region of the time-of-flight mass spectrometer, where ions are extracted into the TOF section at a repetition rate of 83.3 kHz. Each extraction generates a complete mass spectrum, which is processed by a fast (sampling rate 1 Gs/s) data acquisition board and a PC. Particle size information is obtained by chopping the particle beam followed by time-resolved detection of the particle evaporation events. Due to the capability of the time-of-flight mass spectrometer of measuring complete mass spectra for every extraction, complete single particle mass spectra can be collected. This mode provides quantitative information on single particle composition. The TOF-AMS allows a direct measurement of internal and external mixture of non-refractory particle components as well as sensitive ensemble average particle composition and chemically resolved size distribution measurements. Here we describe for the first time the TOF-AMS and its operation as well as results from its first field deployment during the PM _2.5 Technology Assessment and Characterization Study—New York (PMTACS-NY) Winter Intensive in January 2004 in Queens, New York. These results show the capability of the TOF-AMS to measure quantitative aerosol composition and chemically resolved size distributions of the ambient aerosol. In addition it is shown that the single particle information collected with the instrument gives direct information about internal and external mixture of particle components.     

Single Scattering Albedo Monitor for Airborne Particulates

We describe a robust, compact, field deployable instrument (the CAPS PM_ssa) that simultaneously measures airborne particle light extinction and scattering coefficients and thus the single scattering albedo (SSA) on the same sample volume. With an appropriate change in mirrors and light source, measurements have been made at wavelengths ranging from 450 to 780 nm. The extinction measurement is based on cavity attenuated phase shift (CAPS) techniques as employed in the CAPS PM_ex particle extinction monitor; scattering is measured using integrating nephelometry by incorporating a Lambertian integrating sphere within the sample cell. The scattering measurement is calibrated using the extinction measurement. Measurements using ammonium sulfate particles of various sizes indicate that the response of the scattering channel with respect to measured extinction is linear to within 1% up to 1000 Mm^?1 and can be extended further (4000 Mm^?1) with additional corrections. The precision in both measurement channels is less than 1 Mm^?1 (1s, 1σ). The truncation effect in the scattering channel, caused by light lost at extreme forward/backward scattering angles, was measured as a function of particle size using monodisperse polystyrene latex particles (n = 1.59). The results were successfully fit using a simple geometric model allowing for reasonable extrapolation to a given wavelength, particle index of refraction, and particle size distribution, assuming spherical particles. For sub-micron sized particles, the truncation corrections are comparable to those reported for commercial nephelometers. Measurements of the optical properties of ambient aerosol indicate that the values of the SSA of these particles measured with this instrument (0.91 ± 0.03) using scattering and extinction agreed within experimental uncertainty with those determined using extinction measured by this instrument and absorption measured using a multi-angle absorption photometer (0.89 ± 0.03) where the uncertainties are derived from best estimates of the accuracy of the two approaches.

Copyright 2015 American Association for Aerosol Research     

Laboratory and Ambient Particle Density Determinations using Light Scattering in Conjunction with Aerosol Mass Spectrometry

A light scattering module has been integrated into the current AMS instrument. This module provides the simultaneous measurement of vacuum aerodynamic diameter (d _va) and scattered light intensity (R_LS) for all particles sampled by the AMS above ～180 nm geometric diameter. Particle counting statistics and correlated chemical ion signal intensities are obtained for every particle that scatters light. A single calibration curve converts R_LS to an optical diameter (d _o). Using the relationship between d _va and d _o the LS-AMS provides a real-time, per particle measurement of the density of the sampled aerosol particles. The current article is focused on LS-AMS measurements of spherical, non-absorbing aerosol particles. The laboratory characterization of LS-AMS shows that a single calibration curve yields the material density of spherical particles with real refractive indices (n) over a range from 1.41 < n < 1.60 with an accuracy of about ±10%. The density resolution of the current LS-AMS system is also shown to be 10% indicating that externally mixed inorganic/organic aerosol distributions can be resolved. In addition to the single particle measurements of d _va and R_LS, correlated chemical ion signal intensities are obtained with the quadrupole mass spectrometer. A comparison of the particle mass derived from the physical (R_LS and d _va) and chemical measurements provides a consistency check on the performance of the LS-AMS. The ability of the LS-AMS instrument to measure the density of ambient aerosol particles is demonstrated with sample results obtained during the Northeast Air Quality Study (NEAQS) in the summer of 2004.     

Analysis of Aerosolized Particulates of Feedyards Located in the Southern High Plains of Texas

The objective of this study was to quantify, size, and examine the composition of particulates found in ambient aerosolized dust of four large feedyards in the Southern High Plains. Ambient air samples (concentration of dust) were collected upwind (background) and downwind of the feedyards. Aerosolized particulate samples were collected using high volume sequential reference ambient air samplers, PM ₁₀ and PM _2.5 , laser strategic aerosol monitors, cyclone air samplers, and biological cascade impactors. Weather parameters were monitored at each feedyard. The overall (main effects and estimable interactions) statistical (P < 0.0001) general linear model statement (GLM) for PM ₁₀ data showed more concentration of dust (μg/m ³ of air) downwind than upwind and more concentration of dust in the summer than in the winter. PM _2.5 concentrations of dust were comparable for 3 of 4 feedyards upwind and downwind, and PM _2.5 concentrations of dust were lower in the winter than in the summer. GLM (P < 0.0001) data for cascade impactor (all aerobic bacteria, Enterococcus spp, and fungi) mean respirable and non-respirable colony forming units (CFU) were 676 ± 74 CFU/m ³ , and 880 ± 119 CFU/m ³ , respectively. The PM ₁₀ geometric mean size (±GSD) of particles were analyzed in aerosols of the feedyards (range 1.782 ± 1.7 μm to 2.02 ± 1.74μm) and PM _2.5 geometric mean size particles were determined (range 0.66 ± 1.76 μm to 0.71 ± 1.71 μm). Three of 4 feedyards were non-compliant for the Environmental Protection Agency (EPA) concentration standard (150 μg/m ³ /24 h) for PM ₁₀ particles. This may be significant because excess dust may have a negative impact on respiratory disease.     

Evaluation of PM2.5 Size Selectors Used in Speciation Samplers

The separation characteristics of the PM_2.5 aerosol size selectors used in speciation samplers developed for the U.S. EPA National PM_2.5 Chemical Speciation Trends Network were evaluated under clean conditions. Measurement of particle penetration versus aerodynamic diameter was conducted using an APS 3320 in conjunction with a polydisperse test dust. The resulting penetration curves were integrated with assumed ambient particle size distributions (40 CFR Part 53, Subpart F) to obtain an estimate of measured mass concentration and to predict bias relative to the PM_2.5 reference separator. The cutpoint of two sharp cut cyclones, from the family of cyclones developed by Kenny and Gussman (1997), compares favorably with the WINS, although possessing a slight tail that extends into the coarse particle mode. A second cyclone used by the Andersen Corp., AN 3.68, demonstrated the sharpest cut characteristics of the devices tested; however, it possesses a     

Reducing Particle Bounce and Loading Effect for a Multi-Hole Impactor

Aerosol sampling is used to evaluate the health hazards associated with particles deposited in the human breathing system. Impactors, which are extensively employed as aerosol samplers, have low collection efficiency because of particle bounce. The impaction plate is typically coated with oil or grease to prevent particle bounce. However, such coating materials cannot sustain long-term heavy particle loading.

In this study, the impaction plate was recessed, forming a cavity filled with Trypticase Soy Agar (TSA) to reduce particle bounce and re-entrainment. An ultrasonic atomizing nozzle was employed to generate challenge aerosols. An Aerodynamic Particle Sizer (APS) was utilized to measure the number concentrations and the size distributions upstream and downstream of the size-selective devices. A multi-hole impactor and Personal Environmental Monitor PM _2.5 (PEM–PM _2.5 ) were used to evaluate particle bounce and heavy particle loading. Liquid type-Dioctyl phthalate (DOP), soluble solid type-potassium sodium tartrate tetrahydrate (PST) and insoluble solid type-polymethyl methacrylate (PMMA) were investigated, as were different impaction surfaces/surface combinations. The multi-hole impactor coated with silicone oil was compared with a TSA-filled plate. Laboratory results demonstrate that the solid PST particles bounced off the TSA-filled plate less than off the silicone-coated aluminum plate. This study also used a 700-μm-thick layer of silicone oil to prevent TSA dehydration. The experimental results revealed that the silicone-TSA double layer minimized PST particle bounce during the two-hour heavy sampling (mass concentration was around 7.22 mg/m ³ ). Moreover, the PEM-PM _2.5 impactor yielded consistent results when the silicone-TSA double layer method was used. These results are useful for designing bounce-free impaction substrates during heavy load sampling.     

Design and Performance of a New Personal Aerosol Monitor

Three particle size fractions of airborne dust are defined in Euro pean and U.S. standards for health-related dust measurements at the workplace: the respirable, the thoracic, and the inhalable fraction. We developed a novel instrument for personal, time-resolved concentration monitoring and sampling of these three fractions. The instrument combines inertial classification, filter sam pling, and photometric aerosol detection. It consists of a two-stage virtual impactor (cut-off diameters of 4 and 10 mu m), three filters, and three light scattering photometers. The virtual impactor serves as a particle size classifier and a coarse particle concentrator. This enrichment compensates for the decreasing particle mass-based photometric sensitivity with increasing particle diameter. The optical sensors are calibrated in-situ via the mass concentrations obtained gravimetrically from the filter samples. The device operates at a flow rate of 3.1 l min. There is strong agreement between the experimentally determined particle size-dependent collection efficiencies and the definition curves of the corresponding dust fractions. The size dependence of the sensitivity of the inertial concentrator and photometric detection units follow the definition curves qualitatively. Exposure data were obtained for different workplace environments characterized by temporally and spatially highly fluctuating concentrations. The field measurements have shown that the instrument is practicable under rough industrial conditions and that it enables a more comprehensive and more realistic characterization of the individ ual exposure of workers to health-endangering dusts than was previously possible.     

Characterization of Short-Term Particulate Matter Events by Real-Time Single Particle Mass Spectrometry

Single particle measurements were made in Baltimore, Maryland from March to December 2002 using a real-time single particle mass spectrometer, RSMS-3. Particle composition classes were identified that indicated how the aerosol composition changed with time. The results were compared with collocated instruments giving particle number concentrations and size distributions, sulfate, nitrate, organic, and elemental carbon mass concentrations and total mass. Examination of these measurements revealed several particulate matter (PM) events in which the 24 h averaged PM _2.5 mass exceeded 30 μ g/m ³ . Three of these events were studied in further detail by comparing number and mass concentrations obtained by RSMS-3 with standard methods. For all three events, the number concentrations obtained with RSMS-3 and a scanning mobility particle sizer were highly correlated (R ² ～ 0.7). For the event characterized by a high sulfate mass concentration, the RSMS-3 provided an accurate measure of time-dependent nitrate and carbon mass concentrations, but not for sulfate and total mass. For the two events characterized by high carbon mass concentrations (one from a transcontinental wildfire and the other from stagnation during a period of high traffic), RSMS-3 provided an accurate measure of time-dependent nitrate mass, carbon mass and total mass when the aerosol was not dominated by particles outside the size limit of RSMS-3. While the time dependencies were strongly correlated, the absolute mass or number concentrations determined by RSMS-3 were sometimes off by a constant value, which permitted the relative detection efficiencies of some particle classes to be estimated. Other factors that inhibit reconciliation of mass- and number- based concentration measurements are discussed including the difficulty of detecting ammonium sulfate by laser ablation/ionization and the varying size ranges of different particle measurement methods.     

Characterization of Fine Particulate Emissions from Casting Processes

Fine particle (PM_2.5) emission rates and compositions from gray iron metal casting foundry were characterized for No-Bake molds poured at the Research Foundry located at Technikon, LLC (McClellan, CA). For each mold, PM_2.5 was collected for chemical analysis, and particle size distributions were measured by an Electrical Low Pressure Impactor (ELPI) to understand PM emissions during different part of the casting process. Molds prepared with phenolic urethane binders were poured with Class 30 gray cast iron at 1,427–1,480°C. PM_2.5 was collected from the pouring, cooling, and shakeout processes for each mold. Most of the PM_2.5 mass emitted from these processes was composed of carbonaceous compounds, including 37–67% organic carbon (OC) and 17–30% elemental carbon (EC). Oxides of aluminum (Al), silicon (Si), calcium (Ca), and iron (Fe) constituted 8–20% of PM_2.5 mass, and trace elements (e.g., K, Ti, Mn, Cu, Zn, and Pb) contributed 3–6%. Chemical abundances in PM were different between pouring and shakeout for each discrete mold. PM_2.5 mass emissions from pouring were 15–25% of the total from each discrete mold. Ultrafine particles (< 0.1 μm) contributed less than 1% of PM_2.5 mass, but nearly all of the particle numbers. Different mechanisms for pouring and shakeout result in variations in chemical abundances and particle size distributions. The highest PM_2.5 mass and number concentrations were observed when shakeout started. PM_2.5 size distributions in mass concentration during shakeout contained particles in the tail of coarse particles (1.6–2.5 μm) and a vapor condensation mode (0.65–1.6 μm). Flame conditions, vaporization, thermal decomposition of organic materials, and the variability of mold breakup during shakeout affect PM emission rates. A detailed chemical speciation for size-segregated PM samples at different process points needs to be conducted at full-scale foundries to obtain emission factors and source profiles applicable to emission inventories, source receptor modeling, and implementation of emission standards.     

Development and evaluation of a palm-sized optical PM2.5 sensor

A new palm-sized optical PM_2.5 sensor has been developed and its performance evaluated. The PM_2.5 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 µm and can measure PM_2.5mass concentrations as high as ～600 µg/m³. Year-round ambient observations were conducted at four urban and suburban sites in Fukuoka, Kadoma, Kasugai, and Tokyo, Japan. Daily averaged PM_2.5 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 PM_2.5 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 PM_2.5 mass concentration data in urban and suburban environments and is applicable to studies on the environmental and health effects of PM_2.5.

Copyright © 2018 American Association for Aerosol Research     

PM10/PM2.5/PM1 Data from a Trichotomous Sampler

ABSTRACT

As part of an effort to determine whether 1 μm or 2.5 μam is the better choice for a new fine particulate matter standard, Professor Virgil A. Marple of the University of Minnesota developed a high volume trichotomous (PM₁₀/PM_2.5 /PM₁) sampler. Two of these samplers were used to obtain particulate matter (PM) samples at a site located in Phoenix, Arizona, from May 1995 through October 1995. All filter samples were analyzed for mass concentrations and a few for elemental and chemical compositions. Relative fractions were determined for PM₁₀, PM_2.5, PM₁, PM_2.5–10, and PM_1–2.5. Calculations were made to evaluate how coarse and fine mode aerosol contributed to the intermediate size range. Results indicated that most of the PM₁₀ in Phoenix was coarse mode PM (windblown dust), which was also a primary contributor to PM₂₅.     

Characteristics of PM2.5 Episodes Revealed by Semi-Continuous Measurements at the Baltimore Supersite at Ponca St

Highly time-resolved measurements of PM_2.5, its major constituents, particle size distributions (9 nm to 20 μ m), CO, NO/NO₂, and O₃, and meteorological parameters were made from February through November 2002, at the Baltimore Supersite at Ponca St. using commercial and prototype semi-continuous instruments. The average PM_2.5 mass concentration during the study period was 16.9 μ g/m³ and a total of 29 PM_2.5 pollution episodes, each in which 24-h averaged PM_2.5 mass concentrations exceeded 30.0 μ g/m³ for one or more days, were observed. Herein, 6 of the worst episodes are discussed. During these events, PM_2.5 excursions were often largely due to elevations in the concentration of one or two of the major species. In addition, numerous short-term excursions were observed and were generally attributable to local sources. Those in OC, EC, nitrate, CO, and NO_x levels were often observed in the morning traffic hours, particularly before breakdown of nocturnal inversions. Moreover, fresh accumulation aerosols from local stationary combustion sources were observed on several occasions, as evidenced by elevations in elemental markers when winds were aligned with sources resulting in PM_2.5 increments of ～ 17 μ g/m³. Overall, the results described herein show that concentrations of PM_2.5 and its major constituents vary enormously on time scales ranging from < 1 hr to several days, thus imposing a more highly complex pattern of pollutant exposure than can be captured by 24-hr integrated methods, alone. The data suggest that control of a limited number of local sources might achieve compliance with daily and annual PM_2.5 standards.     

Chemical Mass Closure and Chemical Characteristics of Ambient Ultrafine Particles and other PM Fractions

Ambient ultrafine particles (UPs or PM _0.1 ), PM _2.5 and PM ₁₀ were investigated at the roadside of Syuefu road in Hsinchu city and in the Syueshan highway tunnel in Taipei, Taiwan. A SMPS (TSI Model 3936), three Dichotomous samplers (Andersen Model SA-241), and three MOUDIs (MSP Model 110) were collocated to determine the PM number and mass concentrations simultaneously. The filter samples were further analyzed for organic carbon (OC), element carbon (EC), water-soluble ions, and trace elements. The OC artifact was studied and quantified using the quartz behind quartz (QBQ) method for all PM fractions. Taking into account the OC artifact, chemical mass closure (ratio of the reconstructed chemical mass to the gravimetrical mass) of PM _0.1 , PM _2.5 , and PM ₁₀ was then calculated and found to be good. The chemical analysis results of UPs at both sites showed that UPs in the present tunnel was mostly contributed from the vehicle emissions while UPs at the roadside was mainly influenced by urban sources.     

PM1.0 and PM2.5 Characteristics in the Roadside Environment of Hong Kong

Daily mass concentrations of PM _1.0 (particles less than 1.0 μm in diameter), PM _2.5 (particles less than 2.5 μm in diameter), organic carbon (OC), and elemental carbon (EC) were measured from January through May 2004 at a heavily trafficked sampling site in Hong Kong (PU). The average concentrations for PM _1.0 and PM _2.5 were 35.9 ± 12.4 μ g cm ^{? 3} and 52.3 ± 18.3 μ g cm ^{? 3} . Carbonaceous aerosols were the dominant species in fine particles, accounting for ～ 45.7% of PM _1.0 and ～ 44.4% of PM _2.5 . During the study period, seven fine-particle episodes occurred, due to the influence of long-range transport of air masses from mainland China. PM _1.0 and PM _2.5 responded in similar ways; i.e., with elevated mass and OC concentrations in those episode days. During the sampling period, PM _1.0 OC and EC generally behaved similarly to the carbonaceous aerosols in PM _2.5 , regardless of seasonal variations and influence by regional pollutions. The low and relatively constant OC/EC ratios in PM _1.0 and PM _2.5 indicated that vehicular emissions were major sources of carbonaceous aerosols. PM _1.0 and PM _2.5 had the same dominant sources of vehicular emissions in winter, while in spring PM _2.5 was more influenced by PM _{1 ? 2.5} (particles 1–2.5 μ m in diameter) that did not form from vehicle exhausts. Therefore, PM _1.0 was a better indicator for vehicular emissions at the Roadside Station.     

Development of an Aerosol Mass Spectrometer for Size and Composition Analysis of Submicron Particles

The importance of atmospheric aerosols in regulating the Earth's climate and their potential detrimental impact on air quality and human health has stimulated the need for instrumentation which can provide real-time analysis of size resolved aerosol, mass, and chemical composition. We describe here an aerosol mass spectrometer (AMS) which has been developed in response to these aerosol sampling needs and present results which demonstrate quantitative mea surement capability for a laboratory-generated pure component NH₄ NO₃ aerosol. The instrument combines standard vacuum and mass spectrometric technologies with recently developed aerosol sampling techniques. A unique aerodynamic aerosol inlet (developed at the University of Minnesota) focuses particles into a narrow beam and efficiently transports them into vacuum where aerodynamic particle size is determined via a particle time-of-flight (TOF) measurement. Time-resolved particle mass detection is performed mass spectrometrically following particle flash vaporization on a resistively heated surface. Calibration data are presented for aerodynamic particle velocity and particle collection efficiency measurements. The capability to measure aerosol size and mass distributions is compared to simultaneous measurements using a differential mobility analyzer (DMA) and condensation particle counter (CPC). Quantitative size classification is demonstrated for pure component NH₄ NO₃ aerosols having mass concentrations 0.25_mu g m -3. Results of fluid dynamics calculations illustrating the performance of the aerodynamic lens are also presented and compared to the measured performance. The utility of this AMS as both a laboratory and field portable instrument is discussed.     

Variability of Particle Number,Black Carbon,and PM10, PM2.5, and PM1 Levels and Speciation: Influence of Road Traffic Emissions on Urban Air Quality

Measurements of particle number concentration (N), black carbon (BC), and PM ₁₀ , PM _2.5 , and PM ₁ levels and speciation were carried out at an urban background monitoring site in Barcelona. Daily variability of all aerosol monitoring parameters was highly influenced by road traffic emissions and meteorology. The levels of N, BC, PM _X , CO, NO, and NO ₂ increased during traffic rush hours, reflecting exhaust, and non-exhaust traffic emissions and then decreased by the effect of breezes and the reduction of traffic intensity. PM _2.5–10 levels did not decrease during the day as a result of dust resuspension by traffic and wind. N showed a second peak, registered in the afternoon and parallel to O ₃ levels and solar radiation intensity, that may be attributed to photochemical nucleation of precursor gases. An increasing trend was observed for PM ₁ levels from 1999 to 2006, related to the increase in the traffic flow and the diesel fleet in Barcelona. PM composition was highly influenced by road traffic emissions, with exhaust emissions being an important source of PM ₁ and dust resuspension processes of PM _2.5–10 , respectively.     

Characterization of an Ambient Coarse Particle Concentrator Used for Human Exposure Studies: Aerosol Size Distributions,Chemical Composition,and Concentration Enrichment

The goals of the experiments described herein involve determining in real time the size, concentration enrichment, and chemical composition of coarse-mode (<2.5 μm) and fine-mode (>2.5 μm) particles within the nonconcentrated and concentrated flows of a coarse particle concentrator used for human exposure studies. The coarse particle concentrator was intended to concentrate ambient particles in the PM_10–2.5 size range before sending them into a human exposure chamber. The aerodynamic size and chemical composition of particles in the upstream and downstream flows of the concentrator were monitored with an aerosol time-of-f1ight mass spectrometer (ATOFMS) for fixed time intervals over the course of three days. Based on the ATOFMS results, it was found that there was no change in the composition of the ten major particle types observed in the upstream and downstream flows of the concentrator under normal operating conditions. Furthermore, no new particle types were detected downstream that were not detected upstream of the concentrator. A characterization of the aerosol chemical composition and its dependence on sampling conditions is also discussed. Aerosol size distributions were measured with three aerodynamic particle-sizing (APS) instruments sampling simultaneously from different regions of the concentrator. The APS size distributions were used to scale ATOFMS data and measure the ambient concentration factors for the coarse particle concentrator and the exposure chamber. The average concentration factor (ratio of inlet number concentration to the outlet number concentration) for the particle concentrator was 60 + 17 for the 2.5–7.2 μm size range before dilution and transport to the exposure chamber. It was observed that not only were coarse particles being concentrated but fine (<2.5 μm) particles were being concentrated as well, with concentration factors ranging from 2–46 for aerodynamic particle sizes from 0.54–2.5 μm.     

Comparison of Two Aerodynamic Lenses as an Inlet for a Single Particle Laser Ablation Mass Spectrometer

By means of a newly designed portable aerosol mass spectrometer SPLAT (Single Particle Laser Ablation Time-of-flight mass spectrometer) for the analysis of single atmospheric aerosol particles we investigated the system performance in dependency on two different aerodynamic lenses (Liu and Schreiner type) capable of focusing particles with diameters ranging from 80 nm to 800 nm and 300 nm to 3000 nm, respectively. By using the pressure regulated Schreiner lens, the instrument is independent of variations in atmospheric pressure which would lead to changing dynamical properties of the aerosol particles. Active pressure control inside the inlet system facilitates airborne measurements without complicated corrections. With the Liu setup no pressure regulation was used. Here the overall efficiency of our instrument was 7% while with the Schreiner setup 2% was achieved. The Liu lens setup is optimal for measuring submicron particles at low particle concentrations. To detect supermicron particles the Schreiner lens setup is favored. Together with these experiments we present key details of the SPLAT setup and its characterization. Our instrument is able to measure simultaneously the size and the chemical composition of individual aerosol particles larger than 300 nm in diameter. It uses forward scattered light of single aerosol particles at two positions to determine their vacuum aerodynamic diameter from the flight time between the two lasers. Chemical analysis of the particles is done by laser ablation mass spectrometry utilizing a bipolar time-of-flight mass spectrometer.     

Morphology and chemistry of fine particles emitted from a Canadian coal-fired power plant

Particles emitted from coal-fired power plants burning subbituminous coal from Alberta, Canada were examined for total particulates (PM) and size fractions PM_>10, PM₁₀, and PM_2.5. The sampling was carried out following EPA Method 201A. Three tests were performed at each station. The emitted particles were examined using SEM/EDX and gravimetric method for the determination of their sizes. The elemental composition of particles was determined using INAA and ICP-MS.The particles emitted from the stack are classified based on their morphologies and chemistries to the following: unburnt carbon, feed-coal minerals such as quartz, and by-products of the dissociation, fractionation, and contamination by minerals in coal.The emitted particles are mostly spherical and their matrices are composed of aluminosilicate minerals containing calcium. The PM_>10 fraction contains small plerospheres, fragments of char, and angular quartz and feldspar particles. The PM₁₀ fraction contains solid spheres and cenospheres, gypsum needles, and particles of char. The PM_2.5 particle size fraction is mostly composed of solid spherical aluminosilicates with some surface enrichment of elements such as Ba, Ca, and Fe.The composition of emitted particles is ferrocalsialic. Most elements in the particle size fractions are Class I or II, such as Al, Ca, and Fe. Cd, Cu, Mo, and Ti were only detected in PM_2.5 fraction.     

Aerosol Light Extinction Measurements by Cavity Attenuated Phase Shift (CAPS) Spectroscopy: Laboratory Validation and Field Deployment of a Compact Aerosol Particle Extinction Monitor

We present laboratory and field measurements of aerosol light extinction ( σ_ep ) using an instrument that employs Cavity Attenuated Phase Shift (CAPS) spectroscopy. The CAPS extinction monitor comprises a light emitting diode (LED), an optical cavity that acts as the sample cell, and a vacuum photodiode for light detection. The particle σ_ep is determined from changes in the phase shift of the distorted waveform of the square-wave modulated LED light that is transmitted through the optical cell. The 3-σ detection limit of the CAPS monitor under dry particle-free air is 3 Mm^–1 for 1s integration time. Laboratory measurements of absolute particle extinction cross section ( σ_ext ) using non-absorbing, monodisperse polystyrene latex (PSL) spheres are made with an average precision of ± 3% (2-σ) at both 445 and 632 nm. A comparison with Mie theory scattering calculations indicates that these results are accurate within the 10% uncertainty stated for the particle number density measurements. The CAPS extinction monitor was deployed twice in 2009 to test its robustness and performance outside of the laboratory environment. During these field campaigns, a co-located Multi Angle Absorption Photometer (MAAP) provided particle light absorption coefficient ( σ_ap) at 635 nm: the single scattering albedo ( ω) of the ambient aerosol particles was estimated by combining the CAPS σ_ep measured at 632 nm with the MAAP σ_ap data. Our initial results show the high potential of the CAPS as lightweight, compact instrument to perform precise and accurate σ_ep measurements of atmospheric aerosol particles in both laboratory and field conditions.