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Black carbon (BC) absorbs solar radiation, leading to a strong but uncertain warming effect on climate. A key challenge in modeling and quantifying BC's radiative effect on climate is predicting enhancements in light absorption that result from internal mixing between BC and other aerosol components. Modeling and laboratory studies show that BC, when mixed with other aerosol components, absorbs more strongly than pure, uncoated BC; however, some ambient observations suggest more variable and weaker absorption enhancement. We show that the lower-than-expected enhancements in ambient measurements result from a combination of two factors. First, the often used spherical, concentric core-shell approximation generally overestimates the absorption by BC. Second, and more importantly, inadequate consideration of heterogeneity in particle-to-particle composition engenders substantial overestimation in absorption by the total particle population, with greater heterogeneity associated with larger model-measurement differences. We show that accounting for these two effects-variability in per-particle composition and deviations from the core-shell approximation- reconciles absorption enhancement predictions with laboratory and field observations and resolves the apparent discrepancy. Furthermore, our consistent model framework provides a path forward for improving predictions of BC's radiative effect on climate. [ABSTRACT FROM AUTHOR]

We investigated the collection efficiency and effective ionization efficiency for secondary organic aerosol (SOA) particles made from α-pinene + O3 using the single-particle capabilities of the Aerosol Mass Spectrometer (AMS). The mean count-based collection efficiency (CEp) for SOA across these experiments is 0.30 (±0.04 S.D.), ranging from 0.25 to 0.40. The mean mass-based collection efficiency (CEm) is 0.49 (0.07 S.D.). This sub-unit collection efficiency and delayed vaporization is attributable to particle bounce in the vaporization region. Using the coupled optical and chemical detection of the light scattering single-particle (LSSP) module 5 of the AMS, we provide clear evidence that "delayed vaporization" is somewhat of a misnomer for these particles: SOA particles that appear within the chopper window do not vaporize at a slow rate; rather, they flash-vaporize, but often not on the initial impact with the vaporizer, and instead upon a subsequent impact with a hot surface in the vaporization region. We also find that the effective ionization efficiency (defined as ions per particle, IPP) decreases with delayed arrival time. CEp is not a function of particle size (for the mobility diameter range investigated, 170-460nm), but we did see a decrease in CEp with thermodenuder temperature, implying that oxidation state and/or volatility can affect CEp for SOA. [ABSTRACT FROM AUTHOR]

The soot particle aerosol mass spectrometer (SP-AMS) instrument combines continuous wave laser vaporization with electron ionization aerosol mass spectrometry to characterize airborne, refractory black carbon (rBC) particles. The laser selectively vaporizes absorbing rBC-containing particles, allowing the SP-AMS to provide direct chemical information on the refractory and non-refractory chemical components, providing the potential to fingerprint various rBC particle types. In this study, SP-AMS mass spectra were measured for 12 types of rBC particles produced by industrial and combustion processes to explore differences in the carbon cluster (Cn+) mass spectra. TheCn+mass spectra were classified into three categories based on their ion distributions, which varied with rBC particle type. The carbon ion distributions were investigated as a function of laser power, electron ionization (on/off), and ion charge (positive or negative). Results indicate that the dominant positive ion-formation mechanism is likely the vaporization of small, neutral carbon clusters followed by electron ionization (C1+to C5+). Significant ion signal from larger carbon cluster ions (and their fragment ions in the small carbon cluster range), including mid carbon (C6+to C29+) and fullerene (greater than C30+) ions, were observed in soot produced under incomplete combustion conditions, including biomass burning, as well as in fullerene-enriched materials. Fullerene ions were also observed at high laser power with electron ionization turned off, formed via an additional ionization mechanism. We expect this SP-AMS technique to find application in the identification of the source and atmospheric history of airborne ambient rBC particles. Copyright 2015 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

We describe a robust, compact, field deployable instrument (the CAPS PMssa) 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 PMexparticle 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−1and 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 [ABSTRACT FROM AUTHOR]

Atmospheric black carbon (BC) warms Earth's climate, and its reduction has been targeted for near-term climate change mitigation. Models that include forcing by BC assume internal mixing with non-BC aerosol components that enhance BC absorption, often by a factor of ~2; such model estimates have yet to be clearly validated through atmospheric observations. Here, direct in situ measurements of BC absorption enhancements (Eabs) and mixing state are reported for two California regions. The observed Eabs is small--6% on average at 532 nm--and increases weakly with photochemical aging. The Eabs is less than predicted from observationally constrained theoretical calculations, suggesting that many climate models may overestimate warming by BC. These ambient observations stand in contrast to laboratory measurements that show substantial Eabs for BC are possible. [ABSTRACT FROM AUTHOR]

Functionalization (oxygen addition) and fragmentation (carbon loss) reactions governing secondary organic aerosol (SOA) formation from the OH oxidation of alkane precursors were studied in a flow reactor in the absence of NOx. SOA precursors were n-decane (n-C10), n-pentadecane (n-C15), n-heptadecane (n-C17), tricyclo[5.2.1.02,6]decane (JP-10), and vapors of diesel fuel and Southern Louisiana crude oil. Aerosol mass spectra were measured with a high-resolution time-of-flight aerosol mass spectrometer, from which normalized SOA yields, hydrogen-to-carbon (H/C) and oxygen-to-carbon (O/C) ratios, and CxHy+, CxHyO+, and CxHyO2+ ion abundances were extracted as a function of OH exposure. Normalized SOA yield curves exhibited an increase followed by a decrease as a function of OH exposure, with maximum yields at O/C ratios ranging from 0.29 to 0.74. The decrease in SOA yield correlates with an increase in oxygen content and decrease in carbon content, consistent with transitions from functionalization to fragmentation. For a subset of alkane precursors (n-C10, n-C15, and JP-10), maximum SOA yields were estimated to be 0.39, 0.69, and 1.1. In addition, maximum SOA yields correspond with a maximum in the CxHyO+ relative abundance. Measured correlations between OH exposure, O/C ratio, and H/C ratio may enable identification of alkane precursor contributions to ambient SOA. [ABSTRACT FROM AUTHOR]

An inter-comparison study of instruments designed to measure the microphysical and optical properties of soot particles was completed. The following mass-based instruments were tested: Couette Centrifugal Particle Mass Analyzer (CPMA), Time-of-Flight Aerosol Mass Spectrometer—Scanning Mobility Particle Sizer (AMS-SMPS), Single Particle Soot Photometer (SP2), Soot Particle-Aerosol Mass Spectrometer (SP-AMS) and Photoelectric Aerosol Sensor (PAS2000CE). Optical instruments measured absorption (photoacoustic, interferometric, and filter-based), scattering (in situ), and extinction (light attenuation within an optical cavity). The study covered an experimental matrix consisting of 318 runs that systematically tested the performance of instruments across a range of parameters including: fuel equivalence ratio (1.8 ≤ φ ≤ 5), particle shape (mass-mobility exponent (Dfm), 2.0 ≤ Dfm ≤ 3.0), particle mobility size (30 ≤ dm≤ 300 nm), black carbon mass (0.07 ≤ mBC ≤ 4.2 fg) and particle chemical composition. In selected runs, particles were coated with sulfuric acid or dioctyl sebacate (DOS) (0.5 ≤ Δrve≤ 201 nm) where Δrve is the change in the volume equivalent radius due to the coating material. The effect of non-absorbing coatings on instrument response was determined. Changes in the morphology of fractal soot particles were monitored during coating and denuding processes and the effect of particle shape on instrument response was determined. The combination of optical and mass based measurements was used to determine the mass specific absorption coefficient for denuded soot particles. The single scattering albedo of the particles was also measured. An overview of the experiments and sample results are presented. [ABSTRACT FROM AUTHOR]

The characterization of volatile and nonvolatile particle materials present in gas turbine exhaust is critical for accurate estimation of the potential impacts of airport activities on local air quality, atmospheric processes, and climate. change. Two field campaigns were performed to collect an extensive set of particle and gaseous emission data for on-wing gas turbine engines. The tests included CFM56, RB211-535E4-B, AE3007, PW4158, and CJ610 engines, providing the opportunity to compare emissions from a wide range of engine technologies. Here we report mass, number, composition, and size data for the nonvolatile (soot) and volatile particles present in engine exhaust. For all engines, soot emissions (Elm-soot) are greater at climbout (85% power) and takeoff (100%) power than idle (4% or 7%) and approach (30%). At the engine exit plane, soot is the only type of particle detected. For exhaust sampled downwind (15-5.0 m) and diluted by ambient air total particle number emissions (Eln-total) increases by about one or two orders of magnitude relative to the engine exit plane, and the increase is driven by volatile particles that have freshly nucleated in the cooling exhaust gas both in the free atmosphere and in the extractive sample lines. Fuel sulfur content is the determining factor for nucleation of new particles in the cooling exhaust gases. Compositional analysis indicates that the volatile particles consist of sulfate and organic materials (EIm-sulfate and EIn-organic). We estimate a lower bound S[IV] to S[VI] conversion efficiency of (0.08 ± 0.01)%, independent of engine technology. Measurements of EIm-organic ranged from about 0.1 mg kg-1 to 40 mg kg-1. Lubrication oil was present in particles emitted by all engines and accounted for over 90% of the particulate organic mass under some conditions. The products of incomplete combustion are a likely source of the remaining volatile organic particle material. [ABSTRACT FROM AUTHOR]

Particulate emission indices (per kg fuel) have been determined by sampling the advected plumes of in-use commercial aircraft at two different airports using a novel approach. Differences are observed in the number, magnitude, and composition of the particle emissions between idle and take-off. At the first airport, Electrical Low Pressure Impactor (ELPI) data indicate that number based emission indices (EI n ) vary by an order of magnitude for take-off plumes from different aircraft. Additionally, EI n values for idle plumes are greater than take-off. At the second airport, EI n values derived from condensation particle counter (CPC) measurements span ∼⃒ an order of magnitude (3–50 × 10 15 particles per kg fuel). The median values of the idle and take-off plumes were 1.8 × 10 16 and 7.6 × 10 15 particles per kg fuel, respectively. For take-off plumes, the magnitude of the particulate emission index is not correlated with NO x at either airport. The surface properties of the particulate emissions in take-off and idle plumes differ significantly as measured by diffusion charging (DC) and photoelectric aerosol sensor (PAS) instruments. Results indicate that take-off plumes are characterized by particles with photoelectric-active surfaces, presumably elemental carbon, whereas idle plumes are composed of non-photoelectric-active constituents and coated soot particles. Measurements of the particulate size distribution (ELPI) show evidence for two modes, one at ∼⃒ 90 nm aerodynamic diameter and a second mode at or below the instrument cutoff ( [ABSTRACT FROM AUTHOR]

Atmospheric aerosols impact the Earth's climate system directly by scattering and absorbing solar radiation, and it is important to characterise the aerosol optical properties in detail. This study reports the development and validation of an airborne dual-wavelength cavity-attenuated phase-shift (CAPS) single monitor, named A2S2 (Aerosol Absorption Spectral Sizer), based on the commercial CAPS single-scattering albedo monitor (CAPS-PM SSA ; Aerodyne), to simultaneously measure the aerosol optical scattering and extinction at both 450 and 630 nm wavelengths. Replaced pressure and temperature sensors and an additional flow control system were incorporated into the A2S2 for its utilisation on board research aircraft measuring within the troposphere. The evaluation of A2S2 characteristics was performed in the laboratory and included the investigation of the signal-to-noise ratio, validation of performance at various pressure levels, optical closure studies and intercomparing with the currently validated techniques. The chamber experiments show that the A2S2 can perform measurements at sample pressures as low as 550 hPa and at sample temperatures as high as 315 K. Based on the Allan analysis results, we have evaluated that the minimum detection limit of the measurements shows that the measurements have a limit accuracy of ∼ 2 Mm-1 at 450 nm and ∼ 1 Mm-1 at 630 nm for 1 Hz measurements of both scattering coefficients (σsca) and extinction coefficients (σext). The optical closure study with size-selected polystyrene latex (PSL) particles shows that the truncation error of the A2S2 is negligible for particles with particle volume diameter (Dp) < 200 nm, while, for the larger sub-micrometre particles, the measurement uncertainty of A2S2 increases but remains less than 20 %. The average factors to correct the truncation error are 1.13 and 1.05 for 450 and 630 nm, respectively. A simplified truncation correction, dependent on the scattering Ångström exponent (SAE), was developed to rectify truncation errors of the future A2S2 field measurement data. The σsca and σext measured by the A2S2 show good agreement with the concurrent measured results from the nephelometer and the CAPS particle extinction monitor (CAPS-PM ex). The absorption coefficient (σabs) derived through the extinction-minus-scattering (EMS) method by the A2S2 also corresponds with the results obtained from the aethalometer. The A2S2 was successfully deployed during an aircraft measurement campaign (Atmospheric ChemistRy Of the Suburban foreSt – ACROSS) conducted in the vicinity of Paris and the surrounding regions. The average SSA measured during the entire ACROSS flight campaign is 0.86 and 0.88 at 450 and 630 nm, respectively, suggesting that light-absorbing organic aerosols play a significant role. The average SAE and absorption Ångström exponent (AAE) varied due to measurements in various pollution conditions. The results presented in this study indicate that the A2S2 instrument is reliable for measuring aerosol σsca and σext at both blue and red wavelengths, and it stands as a viable substitute for future airborne evaluations of aerosol optical properties. [ABSTRACT FROM AUTHOR]

This article presents a validation study of the stochastic particle-resolved aerosol model PartMC with experimental data from an aerosol chamber experiment. For the experiment, a scanning mobility particle sizer and a single-particle soot photometer were used to monitor the aerosol mixing state evolution of two initially externally mixed aerosol populations of ammonium sulfate and black carbon particles undergoing agglomeration. We applied an efficient optimization algorithm (ProSRS) to determine several unconstrained simulation parameters and were able to successfully reproduce number concentrations and size distributions of mixed particles that formed by agglomeration. The PartMC modeling approach in conjunction with the optimization procedure provides a tool for detailed comparisons of chamber experiments and modeling, where aerosol mixing state is the focus of investigation. Copyright © 2019 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

Atmospheric aerosols impact the Earth’s climate system directly by scattering and absorbing solar radiation, and it is important to characterise the aerosol optical properties in detail. This study reports the development and validation of an airborne dual-wavelength cavity-attenuated phase shift-single (CAPS) monitor, named A2S2 (Aerosol Absorption Spectral Sizer) based on the commercial CAPS single scattering albedo monitor (CAPS-PMSSA, Aerodyne), to simultaneously measure the aerosol optical scattering and extinction at both 450 nm and 630 nm wavelengths. New pressure and temperature sensors and an additional flow control system were incorporated into the A2S2 for its utilization onboard research aircraft measuring within the troposphere. The evaluation of A2S2 characteristics was performed in the laboratory and included the investigation of the signal-to-noise ratio, validation of performance at various pressure levels, optical-closure studies and intercomparing with the currently validated techniques. These laboratory characterisation experiments show that the A2S2 can perform measurements at sample pressures as low as 550 hPa and at sample temperatures as high as 315 K, with an uncertainty of 1 Mm-1 at 450 nm and 0.3 Mm-1 at 630 nm for 1 Hz measurements of both scattering coefficients (σsca) and extinction coefficients (σext). The optical-closure study with size-selected polystyrene latex (PSL) particles show that the truncation error of the A2S2 is negligible for particles with particle volume diameter (Dp) < 200 nm, while for the larger sub-micrometre particles, the measurement uncertainty of A2S2 increases but remains less than 20 %. The A2S2 shows good agreement with the validated instruments for the σsca and σext at 450 nm and 630 nm. The A2S2 was successfully deployed during an aircraft measurement campaign (ACROSS) conducted in the vicinity of Paris and the surrounding regions. The average SSA measured during the entire ACROSS flight campaign is 0.86 and 0.88 at 450 nm and 630 nm, respectively, while the Scattering Ångström Exponent (SAE) varies due to measurements in various pollution conditions. The A2S2 measured σsca results exhibit overall good agreement with the nephelometer results, and it successfully produced altitude profile results over the varied background conditions. The results presented in this study indicate that the A2S2 instrument is reliable for measuring aerosol σsca and σext at both blue and red wavelengths, and it is suitable to replace the nephelometer onboard for future aircraft campaigns. [ABSTRACT FROM AUTHOR]

Wildfires are important contributors to atmospheric aerosols and a large source of emissions that impact regional air quality and global climate. In this study, the regional and nearfield influences of wildfire emissions on ambient aerosol concentration and chemical properties in the Pacific Northwest region of the United States were studied using real-time measurements from a fixed ground site located in Central Oregon at the Mt. Bachelor Observatory (~2700 m a.s.l.) as well as near their sources using an aircraft. The regional characteristics of biomass burning aerosols were found to depend strongly on the modified combustion efficiency (MCE), an index of the combustion processes of a fire. Organic aerosol emissions had negative correlations with MCE, whereas the oxidation state of organic aerosol increased with MCE and plume aging. The relationships between the aerosol properties and MCE were consistent between fresh emissions (~1 h old) and emissions sampled after atmospheric transport (6-45 h), suggesting that biomass burning organic aerosol concentration and chemical properties were strongly influenced by combustion processes at the source and conserved to a significant extent during regional transport. These results suggest that MCE can be a useful metric for describing aerosol properties of wildfire emissions and their impacts on regional air quality and global climate. [ABSTRACT FROM AUTHOR]

Wildfires are important contributors to atmospheric aerosols and a large source of emissions that impact regional air quality and global climate. In this study, the regional and nearfield influences of wildfire emissions on ambient aerosol concentration and chemical properties in the Pacific Northwest region of the United States were studied using real-time measurements from a fixed ground site located in Central Oregon at the Mt. Bachelor Observatory (~2700 m a.s.l.) as well as near their sources using an aircraft. The regional characteristics of biomass burning aerosols were found to depend strongly on the modified combustion efficiency (MCE), an index of the combustion processes of a fire. Organic aerosol emissions had negative correlations with MCE, whereas the oxidation state of organic aerosol increased with MCE and plume aging. The relationships between the aerosol properties and MCE were consistent between fresh emissions (~1 h old) and emissions sampled after atmospheric transport (6-45 h), suggesting that biomass burning organic aerosol concentration and chemical properties were strongly influenced by combustion processes at the source and conserved to a significant extent during regional transport. These results suggest that MCE can be a useful metric for describing aerosol properties of wildfire emissions and their impacts on regional air quality and global climate. [ABSTRACT FROM AUTHOR]

An important source of uncertainty in radiative forcing by absorbing aerosol particles is the uncertainty in their morphologies (i.e., the location of the absorbing substance on/in the particles). To examine the effects of particle morphology on the response of an individual black carbon-containing particle in a Single-Particle Soot Photometer (SP2), a series of experiments was conducted to investigate black carbon-containing particles of known morphology using Regal black (RB), a proxy for collapsed soot, as the light-absorbing substance. Particles were formed by coagulation of RB with either a solid substance (sodium chloride or ammonium sulfate) or a liquid substance (dioctyl sebacate), and by condensation with dioctyl sebacate, the latter experiment forming particles in a core-shell configuration. Each particle type experienced fragmentation (observed as negative lagtimes), and each yielded similar lagtime responses in some instances, confounding attempts to differentiate particle morphology using current SP2 lagtime analysis. SP2 operating conditions, specifically laser power and sample flow rate, which in turn affect the particle heating and dissipation rates, play an important role in the behavior of particles in the SP2, including probability of fragmentation. This behavior also depended on the morphology of the particles and on the thermochemical properties of the non-RB substance. Although these influences cannot currently be unambiguously separated, the SP2 analysis may still provide useful information on particle mixing states and black carbon particle sources. Copyright 2015 American Association for Aerosol Research [ABSTRACT FROM PUBLISHER]

Aerosol intensive optical properties, including Ångström exponents for aerosol light extinction (EAEs), scattering (SAEs) and absorption (AAEs) as well as and the single-scattering albedo (SSA), are indicators for aerosol size, chemical composition, radiative behaviour and particle sources. Derivation of these parameters requires the measurement of aerosol optical properties at multiple wavelengths, which usually involves the use of several instruments. Our study aims to quantify the uncertainties in the determination of these intensive properties using an optical closure approach. In our laboratory closure study, we measured the full set of optical properties for a range of light-absorbing particles with different properties externally mixed with ammonium sulfate to generate aerosols with controlled SSA values. The investigated absorbing particle types were fresh combustion soot emitted by an inverted flame soot generator (SOOT; fractal agglomerates), Aquadag (AQ; compact aggregates), Cabot black (BC; compact agglomerates) and an acrylic paint (magic black, shape unknown). The instruments used in this study were two cavity attenuated phase shift particle monitors for single-scattering albedo (CAPS PM SSA 's; λ=450 , 630 nm) for measuring light-extinction and light-scattering coefficients, one integrating nephelometer (λ=450 , 550, 700 nm) for light-scattering coefficients, and one tricolour absorption photometer (TAP; λ=467 , 528, 652 nm) for filter-based light-absorption coefficients. One key finding is that the coefficients of light absorption, scattering and extinction derived from combing the measurements of two independent instruments agree with measurements from single instruments; the slopes of regression lines are equal within reported uncertainties (i.e. closure is observed). Despite closure for measured absorption coefficients, we caution that the estimated uncertainties for absorption coefficients, propagated for the differential method (DM; absorption = extinction minus scattering), can exceed 100 % for atmospherically relevant SSA values (>0.9). This increasing estimated uncertainty with increasing SSA yields AAE values that may be too uncertain for measurements in the range of atmospheric aerosol loadings. We recommend using the DM for measuring AAE values when the SSA < 0.9. EAE- and SAE-derived values achieved closure during this study within stated uncertainties for extinction coefficients greater than 15 Mm -1. SSA values for 450 and 630 nm wavelengths internally agreed with each other within 10 % uncertainty for all instrument combinations and sampled aerosol types, which fulfils the defined goals for measurement uncertainty of 10 % proposed by Laj et al. (2020) for GCOS (Global Climate Observing System) applications. [ABSTRACT FROM AUTHOR]

We report a positive matrix factorization (PMF) analysis of organic particulate material (PM) emissions of aircraft engine exhaust that includes data from five different aircraft engines and two different fuels (petroleum jet fuel and a Fischer-Tropsch fuel) collected over three field missions. PMF of aerosol mass spectrometer (AMS) data was used to identify six distinct factors: two lubrication oil factors, two aliphatic factors, an aromatic factor, and a siloxane factor. Of these, the lubrication oil factors and the siloxane factor were noncombustion sources. The siloxane factor was attributed to silicone tubing used in the sampling system deployed in one of the three missions included in this study, but not the other two. The two lubrication oil factors correlate with the two different lubrication oils used by the aircraft engines evaluated in this study (Mobil II and Air BP) as well as minor differences presumably due to variation in the blend stocks, temperature history, and analytical factors. Overall, the sum of the aliphatic and aromatic factors decreased with increasing power, as expected based on known trends in VOC emissions. The aliphatic #1 factor correlated with soot emissions, especially at power conditions where EIm-soot was greater than 30 mg kg?1. The aliphatic factor #2 mass spectrum shared some similarities with ambient aerosol organic PM present during the tests and correlated most strongly with dilution levels, two observations that suggest that aliphatic #2 contains components found in ambient aerosol. The aromatic factor correlated with benzene emissions, especially at low power conditions were EIm-benzene was greater than 0.03 mg kg?1. Our results improve the current understanding of aircraft PM composition. Copyright 2014 American Association for Aerosol Research [ABSTRACT FROM PUBLISHER]

The optical properties of soot particles in plumes emanating from a high bypass turbofan aircraft engine (V2527) were measured at distances of 40-80 m behind the engine with a cavity-enhanced phase shift (CAPS)-based extinction monitor (known as the CAPS PMex) and a multi-angle absorption photometer, both operating at wavelength ∼630 nm. Integrated plume measurements from the two instruments were highly correlated with each other (r2 > 0.99, N = 12) and with measured carbon dioxide emission concentrations. Ancillary measurements indicated that the soot particle volume-weighted mobility diameter distribution peaked at 60 nm with a full width at half maximum of ∼60 nm. The soot single scattering albedo determined using the absorption and extinction measurements under engine idle conditions was 0.05 ± 0.02 (where the uncertainty represents 2σ precision), in agreement with previous measurements of aircraft exhaust. The engine soot emission index (mass soot per mass fuel burned) for this particular engine, derived from these measurements and a wavelength-specific mass absorption coefficient and the measured in-plume carbon dioxide concentrations, was 225 ± 35 mg kg-1 at engine idle conditions. These results plus more limited data collected from in-use aircraft on the runway indicate that the CAPS extinction monitor can provide (with an appropriate albedo correction) a credible measurement of the engine soot emission index in situations where the time response and sensitivity of particle absorption monitors are not otherwise sufficient. [ABSTRACT FROM AUTHOR]

We present laboratory and field measurements of aerosol light extinction (σep) 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 σep 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 (σext) 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 (σap) at 635 nm: the single scattering albedo (ω) of the ambient aerosol particles was estimated by combining the CAPS σep measured at 632 nm with the MAAP σap data. Our initial results show the high potential of the CAPS as lightweight, compact instrument to perform precise and accurate σep measurements of atmospheric aerosol particles in both laboratory and field conditions. [ABSTRACT FROM AUTHOR]

The Aerodyne Aerosol Mass Spectrometer (AMS) is a useful tool to study ambient particles. To be quantitative, the mass or (number) of particles detected by the AMS relative to the mass (or number) of particles sampled by the AMS, or the AMS collection efficiency (CE), must be known. Here we investigated the effect of particulate phase on AMS CE for ammonium nitrate, ammonium sulfate, mixed ammonium nitrate/ammonium sulfate, and ammonium sulfate particles coated with an organic liquid. Dry, solid ammonium sulfate particles were sampled with a CE of 24 ± 3%. Liquid droplets and solid particles that were thickly coated with a liquid organic were collected with a CE of 100%. Mixed phase particles, solid particles thinly coated with liquid organic, and metastable aqueous ammonium sulfate droplets had intermediate CEs. The higher CEs for liquid particles compared with solid particles were attributed to wet or coated particles tending to stick upon impact with the AMS vaporizer, while a significant fraction of solid particles bounced prior to vaporization/detection. The consistency of single particle signals indicated that the phase (and hence CE) of mixed component particles did not affect the AMS sensitivity to a particular chemical species once volatilization occurred. Particle phase might explain a significant fraction of the variable AMS CEs reported in the literature. For example, ambient particles that were liquid (e.g., composition dominated by ammonium nitrate or acidic sulfate) have been reported to be sampled with 100% CE. In contrast, most ambient particle measurements report CEs of < 100% (typically~ 50%). [ABSTRACT FROM AUTHOR]

A fluidized bed aerosol generator has been designed and built for the purpose of generating a constant output of dry, submicrometer particles with a large number density. The output of the fluidized bed for generating aerosol particles from dry soot powder has been characterized using a differential mobility analyzer and a condensation particle counter. The particle size distribution is bimodal, with a mode in the submicrometer diameter size range and a mode in the supermicrometer diameter size range. The larger diameter mode is fully separated from the smaller mode and can thus be easily removed from the aerosol flow using impaction techniques. The distribution in the submicrometer size range is nearly log-normal, with a count median diameter falling between 0.1 and 0.3 micrometers. A number density of greater than 10[sup 5] particles cm[sup -3] of soot particles in the submicrometer range can be produced, constant to within 25% (1 standard deviation) over a 4 h time period. The number density of particles produced in the submicrometer range was found to vary with the ratio of soot to bronze beads in the bed mixture, whether or not a feed system was used, and nitrogen flow rate through the fluidized bed and feed system. [ABSTRACT FROM AUTHOR]

We report the development and validation of a new humidified aerosol single-scattering albedometer to quantify the effects of water uptake on submicrometer particle optical properties. The instrument simultaneously measures in situ aerosol light extinction (σep) and scattering (σsp) using a cavity-attenuated phase shift-single scattering albedo particulate matter (PM) monitor (CAPS-PMSSA, Aerodyne Research, Inc., Billerica, MA, USA). It retrieves by difference aerosol light absorption (σap) and directly quantifies aerosol single-scattering albedo (SSA), the aerosol "brightness." We custom built a relative humidity (RH) control system using a water vapor-permeable membrane humidifier and coupled it to the CAPS-PMSSA to enable humidified aerosol observations. Our humidified instrument (H-CAPS-PMSSA) overcomes problems with noise caused by mirror purge-flow humidification, heating, and characterizing cell RH. Careful angular truncation corrections in scattering, particularly for larger particles, were combined with empirical observations. Results show that the optimal operational size to be Dp < 400 nm. The H-CAPS-PMSSA was evaluated with several pure single-component aerosols including ammonium sulfate ((NH4)2SO4), absorbing nigrosin, and levoglucosan, an organic biomass smoke tracer. The measured σep, σsp, and the derived optical hygroscopicity parameter (κ) for size-selected ammonium sulfate are in good agreement with literature values. For dry size-selected nigrosin in the 100 < Dp < 400 nm range, SSA values increased from ∼0.3 to 0.65 with increasing Dp. The enhancement in nigrosin σap at RH = 80% was a factor of 1.05–1.20 relative to dry conditions, with the larger particles showing greater enhancement. SSA increased with RH with the largest fractional enhancement measured for the smallest particles. For polydisperse levoglucosan, we measured an optical κ of 0.26 for both light extinction and scattering and negligible absorption. Our new instrument enables reliable observations of the effects of ambient humidity on mixed aerosol optical properties, particularly for light-absorbing aerosols whose climate forcing is uncertain due to measurement gaps. Copyright © 2021 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

The Aerodyne Soot Particle Aerosol Mass Spectrometer (SP-AMS) can operate with one or both of two particle vaporizers: (1) the standard resistively heated tungsten vaporizer (TV) for detection of non-refractory particulate matter (NR-PM), and (2) an intracavity laser vaporizer (LV) for detection of absorbing, refractory materials, including refractory black carbon (rBC), metal nanoparticles, and associated coatings. In addition to using these vaporizers individually, both can be used simultaneously (dual vaporizer, DV, mode), commonly implemented by sequentially turning the laser vaporizer on (DV-Lon) and off (DV-Loff). Recent results in DV mode have shown an apparent enhancement in measured NR-PM signal during DV-Lon compared with DV-Loff, even for inorganic species unlikely to be strongly associated with rBC. The use of dual vaporizers is complicated by different collection efficiencies (CE) of the two vaporizers, potential differences in the relative ionization efficiencies (RIE) for the same species vaporized from the two vaporizers, and potential interference between the two vaporizers due to laser heating of AMS internal components. Here, we investigated the effect of the laser-heating interference on NR-PM signal. We tested a variety of laser baffles to minimize laser-heating interferences and to constrain the alignment of the laser vaporizer and we identified a baffle that meets these criteria and can be incorporated into SP-AMS systems. For well aligned standard and laser vaporizers, laser heating was found to have only a minor effect on the NR-PM ion signals. Most of the observed increases in NR-PM signals during DV-Lon are attributed to vaporizer-specific differences in the CE and RIE values of NR-PM associated with the rBC-containing particles. Copyright © 2020 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

An evaluation of the performance and relative accuracy of a Cavity Attenuated Phase-Shift Single Scattering Albedo Monitor (CAPS PM SSA ; Aerodyne Research, Inc.) was conducted in an optical-closure study with proven technologies: Cavity Attenuated Phase-Shift Particle Extinction Monitor (CAPS PM ex ; Aerodyne Research, Inc.), three-wavelength integrating nephelometer (TSI Model 3563) and three-wavelength filter-based Particle Soot Absorption Photometer (PSAP; Radiance Research Inc.). The evaluation was conducted by connecting the instruments to a controlled aerosol generation system and comparing the measured scattering, extinction and absorption coefficients measured by the CAPS PM SSA with the independent measurements. Three different particle types were used to generate aerosol samples with single-scattering albedos (SSAs) ranging from 0.4 to 1.0 at 630 nm wavelength. The CAPS PM SSA measurements compared well with the proven technologies. Extinction measurement comparisons exhibited a slope of the linear regression line for the full dataset between 1.05 and 1.01, an intercept below ±1.5×10-6 m -1 (±1.5 Mm -1), and a regression coefficient R2>0.99 , whereas scattering measurements had a slope between 0.90 and 1.04, an intercept of less than ±2.0×10-6 m -1 (2.0 Mm -1), and a coefficient R2>0.96. The derived CAPS PM SSA absorption compared well to the PSAP measurements for the small particle sizes and modest (0.4 to 0.6) SSA values tested, with a linear regression slope between 0.90 and 1.07, an intercept of ±3.0×10-6 m -1 (3.0 Mm -1), and a coefficient R2>0.99. For the SSA measurements, agreement was highest (regression slopes within 1 %) for SSA =1.0 particles at extinction levels of per tens of inverse megameters and above; however, as extinctions approach 0, small uncertainties in the baseline can introduce larger errors. SSA measurements for absorbing particles exhibited absolute differences up to 18 %, though it is not clear which measurement had the best relative accuracy. For a given particle type, the CAPS PM SSA instrument exhibited the lowest scatter around the average. This study demonstrates that the CAPS PM SSA is a robust and reliable instrument for the direct measurement of the scattering and extinction coefficients and thus SSA. This conclusion also holds for the indirect measurement of the absorption coefficient with the constraint that the relative accuracy of this particular determination degrades as the SSA and particle size increases. [ABSTRACT FROM AUTHOR]

The U. S. Environmental Protection Agency in collaboration with the U. S. Air Force Arnold Engineering Development Complex conducted the VAriable Response In Aircraft nvPM Testing (VARIAnT) 3 and 4 test campaigns to compare nonvolatile particulate matter (nvPM) emissions measurements from a variety of diffusion flame combustion aerosol sources (DFCASs), including a Cummins diesel engine, a diesel powered generator, two gas turbine start carts, a J85-GE-5 turbojet engine burning multiple fuels, and a Mini-CAST soot generator. The VARIAnT research program was devised to understand reported variability in the ARP6320A sampling system nvPM measurements. The VARIAnT research program has conducted four test campaigns to date with the VARIAnT 3 and 4 campaigns devoted to: (1) assessing the response of three different black carbon mass analyzers to particles of different size, morphology, and chemical composition; (2) characterizing the particles generated by 6 different combustion sources according to morphology, effective density, and chemical composition; and (3) assessing any significant difference between black carbon as determined by the 3 mass analyzers and the total PM determined via other techniques. Results from VARIAnT 3 and 4 campaigns revealed agreement of about 20% between the Micro-Soot Sensor, the Cavity Attenuated Phase Shift (CAPS PM SSA) monitor and the thermal-optical reference method for elemental carbon (EC) mass, independent of the calibration source used. For the LII-300, the measured mass concentrations in VARIAnT 3 fall within 18% and in VARIAnT 4 fall within 27% of the reference EC mass concentration when calibrated on a combustor rig in VARIAnT 3 and on an LGT-60 start cart in VARIAnT 4, respectively. It was also found that the three mass instrument types (MSS, CAPS PM SSA , and LII-300) can exhibit different BC to reference EC ratios depending on the emission source that appear to correlate to particle geometric mean mobility diameter, morphology, or some other parameter associated with particle geometric mean diameter (GMD) with the LII-300 showing a slightly stronger apparent trend with GMD. Systematic differences in LII-300 measured mass concentrations have been reduced by calibrating with a turbine combustion as a particle source (combustor or turbine engine). With respect to the particle size measurements, the sizing instruments (TSI SMPS, TSI EEPS, and Cambustion DMS 500) were found to be in general agreement in terms of size distributions and concentrations with some exceptions. Gravimetric measurements of the total aerosol mass produced by the various DFCAs differed from the reference EC, BC and integrated particle size distribution measured aerosol masses. The measurements of particle size distributions and single particle analysis performed using the miniSPLAT indicated the presence of larger particles (≳150 nm) having more compact morphologies, higher effective density, and a composition dominated by OC and containing ash. This increased large particle fraction is also associated with higher values of single scattering albedo measured by the CAPS PM SSA instrument and higher OC measurements. These measurements indicate gas turbine engine emissions can be a more heterogeneous mix of particle types beyond the original E−31 assumption that engine exit exhaust particles are mainly composed of black carbon. • PA and CAPS BC mass measurement methods have less variability than the LII BC method. • Gravimetric mass 30–40% greater than reference EC and 50–60% greater than BC masses. • Secondary particle mode >150 nm was observed dominated by non-volatile OC and containing ash. • Calibration of LII with a turbine combustion source more effective than other methods. [ABSTRACT FROM AUTHOR]

Biomass burning (BB) emits enormous amounts of aerosol particles and gases into the atmosphere and thereby significantly influences regional air quality and global climate. A dominant particle type from BB is spherical organic aerosol particles commonly referred to as tarballs. Currently, tarballs can only be identified, using microscopy, from their uniquely spherical shapes following impaction onto a grid. Despite their abundance and potential significance for climate, many unanswered questions related to their formation, emission inventory, removal processes, and optical properties still remain. Here, we report analysis that supports tarball formation in which primary organic particles undergo chemical and physical processing within ~3 h of emission. Transmission electron microscopy analysis reveals that the number fractions of tarballs and the ratios of N and O relative to K, the latter a conserved tracer, increase with particle age and that the more-spherical particles on the substrates had higher ratios of N and O relative to K. Scanning transmission X-ray spectrometry and electron energy loss spectrometry analyses show that these chemical changes are accompanied by the formation of organic compounds that contain nitrogen and carboxylic acid. The results imply that the chemical changes increase the particle sphericity on the substrates, which correlates with particle surface tension and viscosity, and contribute to tarball formation during aging in BB smoke. These findings will enable models to better partition tarball contributions to BB radiative forcing and, in so doing, better help constrain radiative forcing models of BB events. [ABSTRACT FROM AUTHOR]

An evaluation of the performance and accuracy of a Cavity Attenuated Phase-Shift Single Scattering Albedo Monitor (CAPS PMssa, Aerodyne Res. Inc.) was conducted in an optical closure study with proven technologies: Cavity Attenuated Phase-Shift Particle Extinction Monitor (CAPS PMex, Aerodyne Res. Inc.); 3-wavelengh Integrating Nephelometer (TSI Model 3563); and 3-wavelength filter-based Particle Soot Absorption Photometer (PSAP, Radiance Research). The evaluation was conducted by connecting the instruments to a controlled aerosol generation system and comparing the measured scattering, extinction, and absorption coefficients measured by the CAPS PMssa with the independent measurements. Three different particle types were used to generate aerosol samples with single-scattering albedos (SSA) ranging from 0.4 to 1.0 at 630 nm wavelength. The CAPS PMssa measurements compared well with the proven technologies. Extinction measurement comparisons exhibited a slope of the linear regression line for the full data set of 0.96 (-0.02/+0.06), an intercept near zero, and a regression coefficient R² > 0.99; whereas, scattering measurements had a slope of 1.01 (-0.07/+0.06), an intercept of less than +/-2 x 10-6 m-1 (Mm-1), and a coefficient R² ∼ 1.0. The derived CAPS PMssa absorption compared well to the PSAP measurements at low levels (< 70 Mm-1) for the small particle sizes and modest (0.4 to 0.6) SSA values tested, with a linear regression slope of 1.0, an intercept of -4 Mm-1, and a coefficient R² = 0.97. Comparisons at higher particle loadings were compromised by loading effects on the PSAP filters. For the SSA measurements, agreement was highest (regression slopes within 1% ) for SSA = 1.0 particles, though the difference between the measured values increased to 9 % for extinction coefficients lower than 55 Mm-1. SSA measurements for absorbing particles exhibited absolute differences up to 18 %, though it is not clear which measurement had the lowest accuracy. For a given particle type, the CAPS PMssa instrument exhibited the lowest scatter around the average. This study demonstrates that the CAPS PMssa is a robust and reliable instrument for the direct measurement of the scattering and extinction coefficients and thus SSA. This conclusion also holds as well for the indirect measurement of the absorption coefficient with the constraint that the accuracy of this particular measurement degrades as the SSA and particle size increases. [ABSTRACT FROM AUTHOR]

Abstract The composition and carbon nanostructure of soot are important parameters influencing health and climate effects, and the efficacy of soot mitigation technologies. We used laser-vaporization, electron-ionization aerosol mass spectrometry (or SP-AMS) to systematically investigate relationships between aerosol mass spectra, carbon nanostructure (HRTEM), and composition (thermal-optical carbon analysis) for soot with varying physicochemical properties. SP-AMS refractory black carbon concentrations (based on C ≤ 5 + clusters) were correlated to elemental carbon (r = 0.98, p < 10−8) and equivalent black carbon (aethalometer) concentrations. The SP-AMS large carbon ( C ≥ 6 + , midcarbons and fullerene carbons) fraction was inversely correlated to fringe length (r = −0.97, p = 0.028) and linearly correlated to the fraction of refractory organic carbon that partially pyrolize during heating (r = 0.89, p < 10−4). This refractory organic carbon material was incompletely detected with conventional aerosol mass spectrometry (flash vaporization at 600 °C). This suggests that (SP-AMS) refractory carbon cluster analysis provides insight to chemical bonding and nanostructures in refractory carbon materials, lowcarbons ( C ≤ 5 + ) indicate mature soot and large carbons indicate refractory organic carbon and amorphous nanostructures related to C 5 -components. These results have implications for assessments of soot particle mixing state and brown carbon absorption in the atmosphere and enable novel, on-line analysis of engineered carbon nanomaterials and soot characteristics relevant for climate and health. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

The Handix Scientific open-path cavity ringdown spectrometer (OPCRDS) was deployed during summer 2016 in Great Smoky Mountains National Park (GRSM). Extinction coefficients from the relatively new OPCRDS and from a more well-established extinction instrument agreed to within 7%. Aerosol hygroscopic growth (f(RH)) was calculated from the ratio of ambient extinction measured by the OPCRDS to dry extinction measured by a closed-path extinction monitor (Aerodyne’s cavity-attenuated phase shift particulate matter extinction monitor [CAPS PMex]). Derived hygroscopicity (relative humidity [RH] < 95%) from this campaign agreed with data from 1995 at the same site and time of year, which is noteworthy given the decreasing trend for organics and sulfate in the eastern United States. However, maximum f(RH) values in 1995 were less than half as large as those recorded in 2016—possibly due to nephelometer truncation losses in 1995. Two hygroscopicity parameterizations were investigated using high-time-resolution OPCRDS+CAPS PMex data, and the κext model was more accurate than the gamma model. Data from the two ambient optical instruments, the OPCRDS and the open-path nephelometer, generally agreed; however, significant discrepancies between ambient scattering and extinction were observed, apparently driven by a combination of hygroscopic growth effects, which tend to increase nephelometer truncation losses and decrease sensitivity to the wavelength difference between the two instruments as a function of particle size. There was not a statistically significant difference in the mean reconstructed extinction values obtained from the original and the revised IMPROVE (Interagency Monitoring of Protected Visual Environments) equations. On average, IMPROVE reconstructed extinction was ~25% lower than extinction measured by the OPCRDS, which suggests that the IMPROVE equations and 24-hr aerosol data are moderately successful in estimating current haze levels at GRSM. However, this conclusion is limited by the coarse temporal resolution and the low dynamic range of the IMPROVE reconstructed extinction. Implications: Although light extinction, which is directly related to visibility, is not directly measured in U.S. National Parks, existing IMPROVE protocols can be used to accurately infer visibility for average humidity conditions, but during the large fraction of the year when humidity is above or below average, accuracy is reduced substantially. Furthermore, nephelometers, which are used to assess the accuracy of IMPROVE visibility estimates, may themselves be biased low when humidity is very high. Despite reductions in organic and sulfate particles since the 1990s, hygroscopicity, particles’ affinity for water, appears unchanged, although this conclusion is weakened by the previously mentioned nephelometer limitations. [ABSTRACT FROM AUTHOR]

Glass transitions from liquid to semi-solid and solid phase states have important implications for reactivity, growth, and cloud-forming (cloud condensation nuclei and ice nucleation) capabilities of secondary organic aerosols (SOAs). The small size and relatively low mass concentration of SOAs in the atmosphere make it difficult to measure atmospheric SOA glass transitions using conventional methods. To circumvent these difficulties, we have adapted a new technique for measuring glass-forming properties of atmospherically relevant organic aerosols. Aerosol particles to be studied are deposited in the form of a thin film onto an interdigitated electrode (IDE) using electrostatic precipitation. Dielectric spectroscopy provides dipole relaxation rates for organic aerosols as a function of temperature (373 to 233 K) that are used to calculate the glass transition temperatures for several cooling or heating rates. IDE-enabled broadband dielectric spectroscopy (BDS) was successfully used to measure the kinetically controlled glass transition temperatures of aerosols consisting of glycerol and four other compounds with selected cooling and heating rates. The glass transition results agree well with available literature data for these five compounds. The results indicate that the IDE-BDS method can provide accurate glass transition data for organic aerosols under atmospheric conditions. The BDS data obtained with the IDE-BDS technique can be used to characterize glass transitions for both simulated and ambient organic aerosols and to model their climate effects. [ABSTRACT FROM AUTHOR]

Glass transitions from liquid to semi-solid and solid phase states have important implications for reactivity, growth, and cloud forming (cloud condensation nuclei and ice nucleation) capabilities of secondary organic aerosols (SOA). The small size and relatively low mass concentration of SOA in the atmosphere make it difficult to measure atmospheric SOA glass transitions using conventional methods. To circumvent these difficulties, we have adopted a new technique for measuring glass forming properties of atmospherically relevant organic aerosols. Aerosol particles to be studied are deposited in the form of a thin film onto an interdigitated electrode (IDE) using electrostatic precipitation. Dielectric spectroscopy provides dipole relaxation rates for organic aerosols as a function of temperature (373 to 233 K) that are used to calculate the glass transition temperatures for several cooling rates. IDE-enabled broadband dielectric spectroscopy (BDS) was successfully used to measure the kinetically controlled glass transition temperatures of glycerol and citric acid aerosols with selected cooling rates. The glass transition results agree well with available literature data for these two compounds. The results indicate that the IDE-BDS method can provide accurate glass transition data for organic aerosols under atmospheric conditions. The BDS data obtained with the IDE-BDS technique can be used to characterize glass transitions for both simulated and ambient organic aerosols and to model their climate effects. [ABSTRACT FROM AUTHOR]

An evaluation of the operation and performance of a Cavity Attenuated Phase-Shift Particle Extinction Monitor (CAPS PMex) was performed for use on board commercial aircraft as part of the research infrastructure IAGOS (In-service Aircraft for a Global Observing System,www.iagos.org). After extensive laboratory testing, a new flow system, using mass flow controllers, was installed to maintain constant purge and sample flows under low and varying pressure conditions. The instrument was then tested for pressures as low as 200 hPa and evaluated against particle-free compressed air and CO2. Extinction coefficients for the studied gases were in close agreement with literature values with differences between 2.2% and 8%, proving that the CAPS technology works at low pressures. The instrument's limit of detection, with respect to 3 times the variability of the background signal for the full pressure range, was 0.2 Mm−1for 60s integration time. During its first research aircraft operations, the IAGOS instrument prototype, composed of one CAPS PMex and one OPC, showed excellent results regarding the stability of the instruments and the potential for characterizing different aerosol types and for estimating the contribution of sub- and super-μm sized particles to aerosol light extinction. Copyright © 2017 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

Blackcarbon is an important constituent of atmospheric aerosolparticle matter (PM) with significant effects on the global radiationbudget and on human health. The soot particle aerosol mass spectrometer(SP-AMS) has been developed and deployed for real-time ambient measurementsof refractory carbon particles. In the SP-AMS, black carbon or metallicparticles are vaporized through absorption of 1064 nm light from aCW Nd:YAG laser. This scheme allows for continuous “soft”vaporization of both core and coating materials. The main focus ofthis work is to characterize the extent to which this vaporizationscheme provides enhanced chemical composition information about aerosolparticles. This information is difficult to extract from standardSP-AMS mass spectra because they are complicated by extensive fragmentationfrom the harsh 70 eV EI ionization scheme that is typically used inthese instruments. Thus, in this work synchotron-generated vacuumultraviolet (VUV) light in the 8–14 eV range is used to measureVUV-SP-AMS spectra with minimal fragmentation. VUV-SP-AMS spectraof commercially available carbon black, fullerene black, and laboratorygenerated flame soots were obtained. Small carbon cluster cations(C+–C5+) were found to dominatethe VUV-SP-AMS spectra of all the samples, indicating that the correspondingneutral clusters are key products of the SP vaporization process.Intercomparisons of carbon cluster ratios observed in VUV-SP-AMS andSP-AMS spectra are used to confirm spectral features that could beused to distinguish between different types of refractory carbon particles.VUV-SP-AMS spectra of oxidized organic species adsorbed on absorbingcores are also examined and found to display less thermally induceddecomposition and fragmentation than spectra obtained with thermalvaporization at 200 °C (the minimum temperature needed to quantitativelyvaporize ambient oxidized organic aerosol with a continuously heatedsurface). The particle cores tested in these studies include blackcarbon, silver, gold, and platinum nanoparticles. These results demonstratethat SP vaporization is capable of providing enhanced organic chemicalcomposition information for a wide range of organic coating materialsand IR absorbing particle cores. The potential of using this techniqueto study organic species of interest in seeded laboratory chamberor flow reactor studies is discussed. [ABSTRACT FROM AUTHOR]

Ethylene glycol (HOCH2CH2OH), used as engine coolant for most on-road vehicles, is an intermediate volatility organic compound (IVOC) with a high Henry's law coefficient. We present measurements of ethylene glycol (EG) vapor in the Caldecott Tunnel near San Francisco, using a proton transfer reaction mass spectrometer (PTR-MS). Ethylene glycol was detected at mass-to-charge ratio 45, usually interpreted as solely coming from acetaldehyde. EG concentrations in bore 1 of the Caldecott Tunnel, which has a 4% uphill grade, were characterized by infrequent (approximately once per day) events with concentrations exceeding 10 times the average concentration, likely from vehicles with malfunctioning engine coolant systems. Limited measurements in tunnels near Houston and Boston are not conclusive regarding the presence of EG in sampled air. Previous PTR-MS measurements in urban areas may have overestimated acetaldehyde concentrations at times due to this interference by ethylene glycol. Estimates of EG emission rates from the Caldecott Tunnel data are unrealistically high, suggesting that the Caldecott data are not representative of emissions on a national or global scale. EG emissions are potentially important because they can lead to the formation of secondary organic aerosol following oxidation in the atmospheric aqueous phase. [ABSTRACT FROM AUTHOR]

Brown carbon (BrC), which may include secondary organic aerosol (SOA), can be a significant climate-forcing agent via its optical absorption properties. However, the overall contribution of SOA to BrC remains poorly understood. Here, correlations between oxidation level and optical properties of SOA are examined. SOA was generated in a flow reactor in the absence of NOx by OH oxidation of gas-phase precursors used as surrogates for anthropogenic (naphthalene, tricyclo[5.2.1.02,6]decane), biomass burning (guaiacol), and biogenic (α-pinene) emissions. SOA chemical composition was characterized with a time-of-flight aerosol mass spectrometer. SOA mass-specific absorption cross sections (MAC) and refractive indices were calculated from real-time cavity ring-down photoacoustic spectrometry measurements at 405 and 532 nm and from UV-vis spectrometry measurements of methanol extracts of filter-collected particles (300 to 600 nm). At 405 nm, SOA MAC values and imaginary refractive indices increased with increasing oxidation level and decreased with increasing wavelength, leading to negligible absorption at 532 nm. Real refractive indices of SOA decreased with increasing oxidation level. Comparison with literature studies suggests that under typical polluted conditions the effect of NOx on SOA absorption is small. SOA may contribute significantly to atmospheric BrC, with the magnitude dependent on both precursor type and oxidation level. [ABSTRACT FROM AUTHOR]

We present measurements of traffic-related pollutants made near the Long Island Expressway (LIE, I-495), in Queens, New York. The Aerodyne Research Inc. (ARI) mobile laboratory (AML) was deployed to map spatial and temporal gradients of gas-phase species and particulate matter (PM) associated with vehicular exhaust in the residential areas near the LIE. We observe that pollutant levels build up during the early morning hours under stable boundary layer conditions yet fall off quickly within 150 m downwind of the highway. An ARI soot particle aerosol mass spectrometer (SP-AMS) provided measurements of the size-resolved chemical composition of refractory black carbon (rBC) and the associated coating species. The average size distribution of the traffic related PM is characterized by a rBC mode centered at ∼100 nm in vacuum aerodynamic diameter, D va (rBC mass fraction ∼50%). A second rBC mode (rBC mass fraction ∼5%) more heavily coated with organic material is also observed at D va ∼500 nm. Positive matrix factorization (PMF) analyses of the traffic-related PM indicates that rBC is mostly associated with hydrocarbon-like organic (HOA) PM. These results are discussed in the context of chemically resolved size distributions and PMF analysis results performed on the SP-AMS stationary data collected at the Queens College site. Finally, we report emission indices (EI) for both fleet-average conditions and single vehicles, including several New York City Metropolitan Transit Authority (MTA) buses, sampled by the AML in “chase” mode during the study. Copyright 2012 American Association for Aerosol Research [ABSTRACT FROM PUBLISHER]

The petrochemical industry is a major source of 1,3-butadiene and styrene emissions within the Houston-Galveston area. Both compounds are listed as hazardous air pollutants by the Environmental Protection Agency (EPA), and the Texas Commission on Environmental Quality (TCEQ) lists 1,3-butadiene as a highly reactive volatile organic compound. The Aerodyne Mobile Laboratory (AML) was deployed in 2009 as part of the Study of Houston Atmospheric Radical Precursor (SHARP) project to survey the petrochemical complexes in the Houston ship channel area for air toxics releases. This paper describes how the AML, equipped with a modified proton transfer reaction mass spectrometer configured to operate with NO+ as the reagent ion, was used to characterize and quantify fugitive emissions. On April 26, 2009, the AML surveyed the Goodyear Tire and Rubber and Texas Petrochemical (GY-TPC) complex by circumnavigating the facility on public roads while making continuous measurements. The extensive suite of trace gas instrumentation onboard the AML was used to identify fugitive emissions of 1,3-butadiene and styrene from the industrial complex and to distinguish them from any interfering mobile sources. The mobile lab detected significantly enhanced concentrations of 1,3-butadiene (30 ppbv max) and styrene (15 ppbv max). These results are examined with respect to the prevailing winds and routine ambient air monitoring data from TCEQ's Milby Park AutoGC, which is located adjacent to the GY-TPC complex. Simple Gaussian point source plume model calculations predict source emission rates that are consistent with reported emission inventories. [ABSTRACT FROM AUTHOR]

Alkene emissions from the petrochemical industry contribute significantly to ozone production in the greater Houston area but are underestimated in emission inventories. It is not well-known which processes (e.g., fugitive emissions, chemical flare emissions, etc.) are responsible for these underreported emissions. We use fast time response and ground-based mobile measurements of numerous trace gas species to characterize alkene plumes from three identified chemical flares in the greater Houston area. We calculate the combustion efficiency and destruction and removal efficiency (DRE) values of these flares using the carbon balance method. All three flares were operating at DRE values lower than required by regulation. An examination of photochemistry in flare exhaust plumes indicates that the impact of direct formaldehyde emissions from flares on ozone formation is small as compared to the impact of alkene emissions. [ABSTRACT FROM AUTHOR]

Pollutant concentrations in the exhaust plumes of individual diesel trucks were measured at high time resolution in a highway tunnel in Oakland, CA, during July 2010. Emission factors for individual trucks were calculated using a carbon balance method, in which pollutants measured in each exhaust plume were normalized to measured concentrations of carbon dioxide. Pollutants considered here include nitric oxide, nitrogen dioxide (NO2), carbon monoxide, formaldehyde, ethene, and black carbon (BC), as well as optical properties of emitted particles. Fleet-average emission factors for oxides of nitrogen (NOx) and BC respectively decreased 30 ± 6 and 37 ± 10% relative to levels measured at the same location in 2006, whereas a 34 ± 18% increase in the average NO2 emission factor was observed. Emissions distributions for all species were skewed with a small fraction of trucks contributing disproportionately to total emissions. For example, the dirtiest 10% of trucks emitted half of total NO2 and BC emissions. Emission rates for NO2 were found to be anticorrelated with all other species considered here, likely due to the use of catalyzed diesel particle filters to help control exhaust emissions. Absorption and scattering cross-section emission factors were used to calculate the aerosol single scattering albedo (SSA, at 532 nm) for individual truck exhaust plumes, which averaged 0.14 ± 0.03. [ABSTRACT FROM AUTHOR]

Atmospheric emissions of gas and particulate matter from a large ocean-going container vessel were sampled as it slowed and switched from high-sulfur to low-sulfur fuel as it transited into regulated coastal waters of California. Reduction in emission factors (EFs) of sulfur dioxide (SO2), particulate matter, particulate sulfate and cloud condensation nuclei were substantial (≥90%). EFs for particulate organic matter decreased by 70%. Black carbon (BC) EFs were reduced by 41%. When the measured emission reductions, brought about by compliance with the California fuel quality regulation and participation in the vessel speed reduction (VSR) program, are placed in a broader context, warming from reductions in the indirect effect of SO4 would dominate any radiative changes due to the emissions changes. Within regulated waters absolute emission reductions exceed 88% for almost all measured gas and particle phase species. The analysis presented provides direct estimations of the emissions reductions that can be realized by California fuel quality regulation and VSR program, in addition to providing new information relevant to potential health and climate impact of reduced fuel sulfur content, fuel quality and vessel speed reductions. [ABSTRACT FROM AUTHOR]

The potential human health and environmental impacts of aircraft gas turbine engine emissions during normal airport operation are issues of growing concern. During the JETS/Aircraft Particle Emissions eXperiment(APEX)-2 and APEX-3 field campaigns, we performed an extensive series of gas phase and particulate emissions measurements of on-wing gas turbine engines, hi all, nine different CFM56 style engines (including both CFM56-3B1 and -7B22 models) and seven additional engines (two RB211-535E4-B engines, three AE3007 engines, one PW4158, and one cJ6108A) were studied to evaluate engine-to-engine variability Specific gas-phase measurements include NO2, NO, and total NOx, HCHO, C2H4, CO, and a range of volatile organic compounds (e.g., benzene, styrene, toluene, naphthalene). A number of broad conclusions can be made based on the gas-phase data set: (1) field measurements of gas-phase emission indices (Els) are generally consistent with ICAO certification values; (2) speciation of gas phase NOx between NO and NO2 is reproducible for different engine types and favors NO2 at low power (and low fuel flow rate) and NO at high power (high fuel flow rate); (3) emission indices of gas-phase organic compounds and CO decrease rapidly with increasing fuel flow rate; (4) plotting El-CO or volatile organic compound Els against fuel flow rate collapses much of the variability between the different engines, with one exception (AE3007); (5) HCHO, ethylene, acetaldehyde, and propene are the most abundant volatile organic compounds present in the exhaust gases that we can detect, independent of engine technology differences. Empirical correlations accurate to within 30% and based on the publicly available engine parameters are presented for estimating EI-NOx and El-NO2. Engine-to-engine variability, unavailability of combustor input conditions, changing ambient temperatures, and complex reaction dynamics limit the accuracy of global correlations for CO or volatile organic compound Els. [ABSTRACT FROM AUTHOR]

A photo-acoustic absorption spectrometer (PAS) and a cavity ring down aerosol extinction spectrometer (CRD-AES) were used, in conjunction with Mie Theory, to measure the refractive index (RI) of absorbing polystyrene spheres (APSS). The PAS and CRD-AES were also used to measure the absorption and extinction enhancement after these APSS were coated in oleic acid. The experimental enhancements were then compared to predictions from coated-sphere Mie Theory. The measured absorption and extinction enhancements both agreed with modeled enhancements to within an average of 5%. A filter-based absorption technique (particle soot absorption photometer, PSAP) was also used to measure the absorption by the APSS and showed a significant size-dependent bias, as evidenced by the filter-based method measuring significantly lower absorption for both uncoated and coated APSS compared to the PAS. These results suggest the validity of applying photo-acoustics to measure the absorption enhancement created by semi-volatile atmospheric species coating absorbing particles. [ABSTRACT FROM AUTHOR]

We report evidence that carbon impregnated conductive silicone tubing used in aerosol sampling systems can introduce two types of experimental artifacts: (1) silicon tubing dynamically absorbs carbon dioxide gas, requiring greater than 5 minutes to reach equilibrium and (2) silicone tubing emits organic contaminants containing siloxane that are adsorbed onto particles traveling through it and onto downstream quartz fiber filters. The consequence can be substantial for engine exhaust measurements as both artifacts directly impact calculations of particulate mass-based emission indices. The emission of contaminants from the silicone tubing can result in overestimation of organic particle mass concentrations based on real-time aerosol mass spectrometry and the off-line thermal analysis of quartz filters. The adsorption of siloxane contaminants can affect the surface properties of aerosol particles; we observed a marked reduction in the water-affinity of soot particles passed through conductive silicone tubing. These combined observations suggest that the silicone tubing artifacts may have wide consequence for the aerosol community and the tubing should, therefore, be used with caution. Contamination associated with the use of silicone tubing was observed at ambient temperature and, in some cases, was enhanced by mild heating (<70°C) or pre-exposure to a solvent (methanol). Further evaluation is warranted to quantify systematically how the contamination responds to variations in system temperature, physicochemical particle properties, exposure to solvent, sample contact time, tubing age, and sample flow rates. [ABSTRACT FROM AUTHOR]

Abstract: A novel charge-based technique for classifying fractal-like aerosol agglomerates based on their morphology is demonstrated. The study discusses the application of this technique to flame soot aerosols where singly and doubly net-charged agglomerates of similar sizes were segregated using electrostatic classifiers and shown to have different morphologies. The flexibility and simplicity of this technique does not limit its application to aerosols, making it an attractive candidate for performing particle shape selection of different types of nano and micromaterials. [Copyright &y& Elsevier]

A recently developed method to rapidly quantify the elemental composition of bulk organic aerosols (OA) using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) is improved and applied to ambient measurements. Atomic oxygen-to-carbon (O/C) ratios characterize the oxidation state of OA, and O/C from ambient urban OA ranges from 0.2 to 0.8 with a diurnal cycle that decreases with primary emissions and increases because of photochemical processing and secondary OA (SOA) production. Regional O/C approaches 0.9. The hydrogen-to-carbon (H/C, 1.4-1.9) urban diurnal profile increases with primary OA (POA) as does the nitrogen-to-carbon (N/C, ∼0.02). Ambient organic-mass-to-organic-carbon ratios (OM/OC) are directly quantified and correlate well with O/C (R² = 0.997) for ambient OA because of low N/C. Ambient O/C and OM/OC have values consistent with those recently reported from other techniques. Positive matrix factorization applied to ambient OA identifies factors with distinct O/C and OM/OC trends. The highest O/C and OM/OC (1.0 and 2.5, respectively) are observed for aged ambient oxygenated OA, significantly exceeding values for traditional chamber SOA, while laboratory-produced primary biomass burning OA (BBOA) is similar to ambient BBOA, O/C of 0.3-0.4. Hydrocarbon-like OA (HOA), a surrogate for urban combustion POA, has the lowest O/C (0.06-0.10), similar to vehicle exhaust An approximation for predicting O/C from unit mass resolution data is also presented. [ABSTRACT FROM AUTHOR]

The emissions from in-use commercial aircraft engines have been analyzed for selected gas-phase species and particulate characteristics using continuous extractive sampling 1-2 mm downwind from operational taxi- and runways at Hartsfield- Jackson Atlanta international Airport. Using the aircraft tail numbers, 376 plumes were associated with specific engine models. In general, for takeoff plumes, the measured NO~ emission index is lower (`--~18%) than that predicted by engine certification data corrected for ambient conditions. These results are an in-service observation of the practice of "reduced thrust takeoff". The CO emission index observed in ground idle plumes was greater (up to 100%) than predicted by engine certification data for the 7% thrust condition. Significant differences are observed in the emissions of black carbon and particle number among different engine models/technologies. The presence of a mode at ~-~65 nm (mobility diameter) associated with takeoff plumes and a smaller mode at `~25 nm associated with idle plumes has been observed. An anticorrelation between particle mass loading and particle number concentration is observed. [ABSTRACT FROM AUTHOR]

The size-dependent particle transmission efficiency of the aerodynamic lens system used in the Aerodyne Aerosol Mass Spectrometer (AMS) was investigated with computational fluid dynamics (CFD) calculations and experimental measurements. The CFD calculations revealed that the entire lens system, including the aerodynamic lens itself, the critical orifice which defines the operating lens pressure, and a valve assembly, needs to be considered. Previous calculations considered only the aerodynamic lens. The calculations also investigated the effect of operating the lens system at two different sampling pressures, 7.8 × 104 Pa (585 torr) and 1.0 × 105 Pa (760 torr). Experimental measurements of transmission efficiency were performed with size-selected diethyl hexyl sebacate (DEHS), NH4NO3, and NaNO3 particles on three different AMS instruments at two different ambient sampling pressures (7.8 × 104 Pa, 585 torr and 1.0 × 105 Pa, 760 torr). Comparisons of the measurements and the calculations show qualitative agreement, but there are significant deviations which are as yet unexplained. On the small size end (30 nm to 150 nm vacuum aerodynamic diameter), the measured transmission efficiency is lower than predicted. On the large size end (> 350 nm vacuum aerodynamic diameter) the measured transmission efficiency is greater than predicted at 7.8 × 104 Pa (585 torr) and in good agreement with the prediction at 1.0 × 105 Pa (760 torr). [ABSTRACT FROM AUTHOR]

Mobility-selected fractal and non-fractal soot particles (mobility diameters dm = 135 to 310 nm) were produced at three controlled fuel equivalence ratios (φ = 2.1, 3.5, and 4.5) by an ethylene/oxygen flame. Oleic acid (liquid) and anthracene (solid) coatings were alternately applied to the particles and removed. Simultaneous measurements with an Aerodyne aerosol mass spectrometer and a scanning mobility particle sizer yielded the particle mass, volume, density, composition, dynamic shape factor, fractal dimension, surface area, and the size and number of the primary spherules forming the fractal aggregate. For a given φ, the diameters of the primary spherules are approximately the same, independent of dm (15 nm, 35 nm, and 55 nm for φ = 2.1, 3.5, and 4.5, respectively). As the coating thickness on a particle increases, the dynamic shape factor decreases but dm remains constant until the particle reaches a spherical (for oleic acid) or non-fractal but irregular (for anthracene) shape. Under some conditions, liquid oleic acid coating causes the internal BC framework to rearrange into a more compact configuration. The surface area of fractal particles is up to 2.4 times greater than that of a sphere with the same dm. Using the surface area determinations, the time for a fractal particle to obtain a monolayer of coating material is compared to that of spheres. If it is assumed that the fractal particle is a sphere with the same dm as the fractal particle, the monolayer coating time is underestimated by a factor of up to 1.7. [ABSTRACT FROM AUTHOR]