Special Issue "Morphology and Internal Mixing of Atmospheric Particles"

A special issue of Atmosphere (ISSN 2073-4433). This special issue belongs to the section "Aerosols".

Deadline for manuscript submissions: closed (15 November 2017).

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editors

Guest Editor
Dr. Swarup China Website E-Mail
William R. Wiley Environmental Molecular Sciences Laboratory , Pacific Northwest National Laboratory, 902 Battelle Blvd, Richland, WA 99354, USA
Interests: aerosol morphology and optical properties; ice nucleation; multiphase atmospheric chemistry
Guest Editor
Dr. Claudio Mazzoleni Website E-Mail
Physics Department and Atmospheric Sciences Program, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA
Interests: aerosol physical and optical properties; aerosol-cloud interactions; atmospheric instrumentation

Special Issue Information

Dear Colleagues,

The lack of mechanistic knowledge on several aerosol properties and their complex interactions with clouds and radiation hinders the advance in predictive understanding of climatic and environmental impacts of atmospheric aerosol. Single particle morphology and internal mixing states are among those aerosol aspects that are the least known and characterized, due to their complexity and inherent measurement challenges. However, these single-particle aspects influence the aerosol optical properties, as well as various microphysical processes like hygroscopicity and heterogeneous ice nucleation. During the aerosol life cycle, particles experience several atmospheric aging processes, such as restructuring, coagulation and condensation with organic and inorganic materials, and heterogeneous chemical reactions. These processes result in changes in morphology and internal mixing state of individual particles. The significance of these effects and, hence, the impact on atmospheric radiation budget, is largely unconstrained and not well understood.

New experimental, as well as modeling, efforts are needed to better understand the role of aerosol morphology and internal mixing at the single-particle level. This Special Issue focuses on this timely topic, and we welcome both laboratory and field measurements, as well as modeling efforts that investigate the morphology and internal mixing of atmospheric particle, their chemical and physical interactions with the environment and their effects, for example, on optical properties and microphysical processes.

Dr. Swarup China
Dr. Claudio Mazzoleni
Guest Editors

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Keywords

  • atmospheric particles

  • morphology

  • internal mixing

  • single particle analysis and modeling

  • aerosol optical properties

  • radiative forcing

  • aerosol-cloud interactions

  • heterogeneous aerosol chemistry

  • aerosol imaging

  • microscopy

Published Papers (13 papers)

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Editorial

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Open AccessEditorial
Preface: Morphology and Internal Mixing of Atmospheric Particles
Atmosphere 2018, 9(7), 249; https://doi.org/10.3390/atmos9070249 - 04 Jul 2018
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Research

Jump to: Editorial

Open AccessArticle
Immersion Freezing of Total Ambient Aerosols and Ice Residuals
Atmosphere 2018, 9(2), 55; https://doi.org/10.3390/atmos9020055 - 09 Feb 2018
Cited by 2
Abstract
This laboratory study evaluates an experimental set-up to study the immersion freezing properties of ice residuals (IRs) at a temperature ranging from −26 to −34 °C using two continuous-flow diffusion chamber-style ice nucleation chambers coupled with a virtual impactor and heat exchanger. Ice [...] Read more.
This laboratory study evaluates an experimental set-up to study the immersion freezing properties of ice residuals (IRs) at a temperature ranging from −26 to −34 °C using two continuous-flow diffusion chamber-style ice nucleation chambers coupled with a virtual impactor and heat exchanger. Ice was nucleated on the total ambient aerosol through an immersion freezing mechanism in an ice nucleation chamber (chamber 1). The larger ice crystals formed in chamber 1 were separated and sublimated to obtain IRs, and the frozen fraction of these IRs was investigated in a second ice nucleation chamber (chamber 2). The ambient aerosol was sampled from a sampling site located in the Columbia Plateau region, WA, USA, which is subjected to frequent windblown dust events, and only particles less than 1.5 μm in diameter were investigated. Single-particle elemental composition analyses of the total ambient aerosols showed that the majority of the particles are dust particles coated with organic matter. This study demonstrated a capability to investigate the ice nucleation properties of IRs to better understand the nature of Ice Nucleating Particles (INPs) in the ambient atmosphere. Full article
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Open AccessArticle
Influence of Common Assumptions Regarding Aerosol Composition and Mixing State on Predicted CCN Concentration
Atmosphere 2018, 9(2), 54; https://doi.org/10.3390/atmos9020054 - 08 Feb 2018
Cited by 4
Abstract
A 4-year record of aerosol size and hygroscopic growth factor distributions measured at the Department of Energy’s Southern Great Plains (SGP) site in Oklahoma, U.S. were used to estimate supersaturation (S)-dependent cloud condensation nuclei concentrations (NCCN). Baseline or reference NCCN [...] Read more.
A 4-year record of aerosol size and hygroscopic growth factor distributions measured at the Department of Energy’s Southern Great Plains (SGP) site in Oklahoma, U.S. were used to estimate supersaturation (S)-dependent cloud condensation nuclei concentrations (NCCN). Baseline or reference NCCN(S) spectra were estimated using κ-Köhler Theory without any averaging of the measured distributions by creating matrices of size- and hygroscopicity-dependent number concentration (N) and then integrating for S > critical supersaturation (Sc) calculated for the same size and hygroscopicity pairs. Those estimates were first compared with directly measured NCCN at the same site. Subsequently, NCCN was calculated using the same dataset but with an array of simplified treatments in which the aerosol was assumed to be either an internal or an external mixture and the hygroscopicity either assumed or based on averages derived from the growth factor distributions. The CCN spectra calculated using the simplified treatments were compared with those calculated using the baseline approach to evaluate the error introduced with commonly used approximations. Full article
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Open AccessArticle
Physicochemical Characteristics of Individual Aerosol Particles during the 2015 China Victory Day Parade in Beijing
Atmosphere 2018, 9(2), 40; https://doi.org/10.3390/atmos9020040 - 25 Jan 2018
Cited by 4
Abstract
During the 2015 China Victory Day parade control periods, the air quality in Beijing hit the best record, leading to 15 continuous good days with an average PM2.5 mass concentration 18 μg/m3, which provided a unique opportunity to study the [...] Read more.
During the 2015 China Victory Day parade control periods, the air quality in Beijing hit the best record, leading to 15 continuous good days with an average PM2.5 mass concentration 18 μg/m3, which provided a unique opportunity to study the ambient aerosols in megacity Beijing. The morphology and elemental composition of aerosol particles were investigated by transmission electron microscopy coupled with energy dispersive X-ray spectrometry (TEM-EDX). Five types of individual particles were identified, including homogeneous mixed S-rich particles (HS; 44.9%), organic coated S-rich particles (CS; 34.3%), mineral particles (10.5%), soot aggregates (7.21%) and organic particles (3.2%). The number percentage of secondary particles (including HS and CS) accounted for a large proportion with 79.2% during the control periods. The average diameter of secondary particles increased with relative humidity (RH), being 323 nm, 358 nm and 397 nm at the RH 34%, 43% and 53%, respectively, suggesting that the high RH might favor the growth of secondary particles. The higher proportion of CS particles may show great atmospheric implications and the CS particles may be formed by the condensation of secondary organic aerosols on pre-existing S-rich particles. Full article
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Open AccessArticle
Quantifying Impacts of Aerosol Mixing State on Nucleation-Scavenging of Black Carbon Aerosol Particles
Atmosphere 2018, 9(1), 17; https://doi.org/10.3390/atmos9010017 - 11 Jan 2018
Cited by 7
Abstract
Recent observational studies suggest that nucleation-scavenging is the principal path to removing black carbon-containing aerosol from the atmosphere, thus affecting black carbon’s lifetime and radiative forcing. Modeling the process of nucleation-scavenging is challenging, since black carbon (BC) forms complex internal mixtures with other [...] Read more.
Recent observational studies suggest that nucleation-scavenging is the principal path to removing black carbon-containing aerosol from the atmosphere, thus affecting black carbon’s lifetime and radiative forcing. Modeling the process of nucleation-scavenging is challenging, since black carbon (BC) forms complex internal mixtures with other aerosol species. Here, we examined the impacts of black carbon mixing state on nucleation scavenging using the particle-resolved aerosol model PartMC-MOSAIC. This modeling approach has the unique advantage that complex aerosol mixing states can be represented on a per-particle level. For a scenario library that comprised hundreds of diverse aerosol populations, we quantified nucleation-scavenged BC mass fractions. Consistent with measurements, these vary widely, depending on the amount of BC, the amount of coating and coating material, as well as the environmental supersaturation. We quantified the error in the nucleation-scavenged black carbon mass fraction introduced when assuming an internally mixed distribution, and determined its bounds depending on environmental supersaturation and on the aerosol mixing state index χ . For a given χ value, the error decreased at higher supersaturations. For more externally mixed populations ( χ < 20 %), the nucleation-scavenged BC mass fraction could be overestimated by more than 1000% at supersaturations of 0.1%, while for more internally mixed populations ( χ > 75 %), the error was below 100% for the range of supersaturations (from 0.02% to 1%) investigated here. Accounting for black carbon mixing state and knowledge of the supersaturation of the environment are crucial when determining the amount of black carbon that can be incorporated into clouds. Full article
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Open AccessArticle
Machine Learning to Predict the Global Distribution of Aerosol Mixing State Metrics
Atmosphere 2018, 9(1), 15; https://doi.org/10.3390/atmos9010015 - 09 Jan 2018
Cited by 5
Abstract
Atmospheric aerosols are evolving mixtures of chemical species. In global climate models (GCMs), this “aerosol mixing state” is represented in a highly simplified manner. This can introduce errors in the estimates of climate-relevant aerosol properties, such as the concentration of cloud condensation nuclei. [...] Read more.
Atmospheric aerosols are evolving mixtures of chemical species. In global climate models (GCMs), this “aerosol mixing state” is represented in a highly simplified manner. This can introduce errors in the estimates of climate-relevant aerosol properties, such as the concentration of cloud condensation nuclei. The goal for this study is to determine a global spatial distribution of aerosol mixing state with respect to hygroscopicity, as quantified by the mixing state metric χ . In this way, areas can be identified where the external or internal mixture assumption is more appropriate. We used the output of a large ensemble of particle-resolved box model simulations in conjunction with machine learning techniques to train a model of the mixing state metric χ . This lower-order model for χ uses as inputs only variables known to GCMs, enabling us to create a global map of χ based on GCM data. We found that χ varied between 20% and nearly 100%, and we quantified how this depended on particle diameter, location, and time of the year. This framework demonstrates how machine learning can be applied to bridge the gap between detailed process modeling and a large-scale climate model. Full article
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Open AccessArticle
Elemental Mixing State of Aerosol Particles Collected in Central Amazonia during GoAmazon2014/15
Atmosphere 2017, 8(9), 173; https://doi.org/10.3390/atmos8090173 - 15 Sep 2017
Cited by 8
Abstract
Two complementary techniques, Scanning Transmission X-ray Microscopy/Near Edge Fine Structure spectroscopy (STXM/NEXAFS) and Scanning Electron Microscopy/Energy Dispersive X-ray spectroscopy (SEM/EDX), have been quantitatively combined to characterize individual atmospheric particles. This pair of techniques was applied to particle samples at three sampling sites (ATTO, [...] Read more.
Two complementary techniques, Scanning Transmission X-ray Microscopy/Near Edge Fine Structure spectroscopy (STXM/NEXAFS) and Scanning Electron Microscopy/Energy Dispersive X-ray spectroscopy (SEM/EDX), have been quantitatively combined to characterize individual atmospheric particles. This pair of techniques was applied to particle samples at three sampling sites (ATTO, ZF2, and T3) in the Amazon basin as part of the Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) field campaign during the dry season of 2014. The combined data was subjected to k-means clustering using mass fractions of the following elements: C, N, O, Na, Mg, P, S, Cl, K, Ca, Mn, Fe, Ni, and Zn. Cluster analysis identified 12 particle types across different sampling sites and particle sizes. Samples from the remote Amazon Tall Tower Observatory (ATTO, also T0a) exhibited less cluster variety and fewer anthropogenic clusters than samples collected at the sites nearer to the Manaus metropolitan region, ZF2 (also T0t) or T3. Samples from the ZF2 site contained aged/anthropogenic clusters not readily explained by transport from ATTO or Manaus, possibly suggesting the effects of long range atmospheric transport or other local aerosol sources present during sampling. In addition, this data set allowed for recently established diversity parameters to be calculated. All sample periods had high mixing state indices (χ) that were >0.8. Two individual particle diversity (Di) populations were observed, with particles <0.5 µm having a Di of ~2.4 and >0.5 µm particles having a Di of ~3.6, which likely correspond to fresh and aged aerosols, respectively. The diversity parameters determined by the quantitative method presented here will serve to aid in the accurate representation of aerosol mixing state, source apportionment, and aging in both less polluted and more developed environments in the Amazon Basin. Full article
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Open AccessArticle
Effect of Thermodenuding on the Structure of Nascent Flame Soot Aggregates
Atmosphere 2017, 8(9), 166; https://doi.org/10.3390/atmos8090166 - 06 Sep 2017
Cited by 8
Abstract
The optical properties (absorption and scattering) of soot particles depend on soot size and index of refraction, but also on the soot complex morphology and the internal mixing with materials that can condense on a freshly emitted (nascent) soot particle and coat it. [...] Read more.
The optical properties (absorption and scattering) of soot particles depend on soot size and index of refraction, but also on the soot complex morphology and the internal mixing with materials that can condense on a freshly emitted (nascent) soot particle and coat it. This coating can affect the soot optical properties by refracting light, or by changing the soot aggregate structure. A common approach to studying the effect of coating on soot optical properties is to measure the absorption and scattering coefficients in ambient air, and then measure them again after removing the coating using a thermodenuder. In this approach, it is assumed that: (1) most of the coating material is removed; (2) charred organic coating does not add to the refractory carbon; (3) oxidation of soot is negligible; and, (4) the structure of the pre-existing soot core is left unaltered, despite the potential oxidation of the core at elevated temperatures. In this study, we investigated the validity of the last assumption, by studying the effect of thermodenuding on the morphology of nascent soot. To this end, we analyzed the morphological properties of laboratory generated nascent soot, before and after thermodenuding. Our investigation shows that there is only minor restructuring of nascent soot by thermodenuding. Full article
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Open AccessArticle
The Impact of Sampling Medium and Environment on Particle Morphology
Atmosphere 2017, 8(9), 162; https://doi.org/10.3390/atmos8090162 - 29 Aug 2017
Cited by 2
Abstract
Sampling on different substrates is commonly used in laboratory and field studies to investigate the morphology and mixing state of aerosol particles. Our focus was on the transformations that can occur to the collected particles during storage, handling, and analysis. Particle samples were [...] Read more.
Sampling on different substrates is commonly used in laboratory and field studies to investigate the morphology and mixing state of aerosol particles. Our focus was on the transformations that can occur to the collected particles during storage, handling, and analysis. Particle samples were prepared by electrostatic deposition of size-classified sodium chloride, sulfuric acid, and coated soot aerosols on different substrates. The samples were inspected by electron microscopy before and after exposure to various environments. For coated soot, the imaging results were compared against mass-mobility measurements of airborne particles that underwent similar treatments. The extent of sample alteration ranged from negligible to major, depending on the environment, substrate, and particle composition. We discussed the implications of our findings for cases where morphology and the mixing state of particles must be preserved, and cases where particle transformations are desirable. Full article
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Open AccessArticle
Temperature-Dependent Diffusion of H2SO4 in Air at Atmospherically Relevant Conditions: Laboratory Measurements Using Laminar Flow Technique
Atmosphere 2017, 8(7), 132; https://doi.org/10.3390/atmos8070132 - 22 Jul 2017
Cited by 6
Abstract
We report flow tube measurements of the effective sulfuric acid diffusion coefficient at ranges of different relative humidities (from ∼4 to 70%), temperatures (278, 288 and 298 K) and initial H2SO4 concentrations (from 1 × 106 to 1 × [...] Read more.
We report flow tube measurements of the effective sulfuric acid diffusion coefficient at ranges of different relative humidities (from ∼4 to 70%), temperatures (278, 288 and 298 K) and initial H2SO4 concentrations (from 1 × 106 to 1 × 108 molecules·cm−3). The measurements were carried out under laminar flow of humidified air containing trace amounts of impurities such as amines (few ppt), thus representing typical conditions met in Earth’s continental boundary layer. The diffusion coefficients were calculated from the sulfuric acid wall loss rate coefficients that were obtained by measuring H2SO4 concentration continuously at seven different positions along the flow tube with a chemical ionization mass spectrometer (CIMS). The wall loss rate coefficients and laminar flow conditions were verified with additional computational fluid dynamics (CFD) model FLUENT simulations. The determined effective sulfuric acid diffusion coefficients decreased with increasing relative humidity, as also seen in previous experiments, and had a rather strong power dependence with respect to temperature, around ∝ T5.6, which is in disagreement with the expected temperature dependence of ∼T1.75 for pure vapours. Further clustering kinetics simulations using quantum chemical data showed that the effective diffusion coefficient is lowered by the increased diffusion volume of H2SO4 molecules via a temperature-dependent attachment of base impurities like amines. Thus, the measurements and simulations suggest that in the atmosphere the attachment of sulfuric acid molecules with base molecules can lead to a lower than expected effective sulfuric acid diffusion coefficient with a higher than expected temperature dependence. Full article
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Open AccessArticle
Monthly and Diurnal Variation of the Concentrations of Aerosol Surface Area in Fukuoka, Japan, Measured by Diffusion Charging Method
Atmosphere 2017, 8(7), 114; https://doi.org/10.3390/atmos8070114 - 28 Jun 2017
Cited by 3
Abstract
Observation of the ambient aerosol surface area concentrations is important to understand the aerosol toxicity because an increased surface area may be able to act as an enhanced reaction interface for certain reactions between aerosol particles and biological cells, as well as an [...] Read more.
Observation of the ambient aerosol surface area concentrations is important to understand the aerosol toxicity because an increased surface area may be able to act as an enhanced reaction interface for certain reactions between aerosol particles and biological cells, as well as an extended surface for adsorbing and carrying co-pollutants that are originally in gas phase. In this study, the concentration of aerosol surface area was measured from April 2015 to March 2016 in Fukuoka, Japan. We investigated the monthly and diurnal variations in the correlations between the aerosol surface area and black carbon (BC) and sulfate concentrations. Throughout the year, aerosol surface area concentration was strongly correlated with the concentrations of BC, which has a relatively large surface area since BC particles are usually submicron agglomerates consisting of much smaller (tens of nanometers) sized primary soot particles. The slopes of the regression between the aerosol surface area and BC concentrations was highest in August and September 2015. We presented evidence that this was caused by an increase in the proportion of airmasses that originated on the main islands of Japan. This may enhance the introduction of the BC to Fukuoka from the main islands of Japan which we hypothesize to be relatively fresh or “uncoated”, thereby maintaining its larger surface area. Full article
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Open AccessArticle
Q-Space Analysis of the Light Scattering Phase Function of Particles with Any Shape
Atmosphere 2017, 8(4), 68; https://doi.org/10.3390/atmos8040068 - 29 Mar 2017
Cited by 9
Abstract
Q-space analysis is applied to the light scattering phase function of a wide variety of non-spherical and irregularly shaped particles including a great many types of dusts, fractal aggregates, spheroids, irregular spheres, Gaussian random spheres, thickened clusters and nine types of ice crystals. [...] Read more.
Q-space analysis is applied to the light scattering phase function of a wide variety of non-spherical and irregularly shaped particles including a great many types of dusts, fractal aggregates, spheroids, irregular spheres, Gaussian random spheres, thickened clusters and nine types of ice crystals. The phase functions were either experimental data or calculations. This analysis method uncovers many specific and quantitative similarities and differences between the scattering by various shapes and also when compared to spheres. From this analysis a general description for scattering by a particle of any shape emerges with specific details assigned to various shapes. Full article
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Open AccessArticle
Morphology, Composition, and Mixing State of Individual Aerosol Particles in Northeast China during Wintertime
Atmosphere 2017, 8(3), 47; https://doi.org/10.3390/atmos8030047 - 24 Feb 2017
Cited by 6
Abstract
Northeast China is located in a high latitude area of the world and undergoes a cold season that lasts six months each year. Recently, regional haze episodes with high concentrations of fine particles (PM2.5) have frequently been occurring in Northeast China [...] Read more.
Northeast China is located in a high latitude area of the world and undergoes a cold season that lasts six months each year. Recently, regional haze episodes with high concentrations of fine particles (PM2.5) have frequently been occurring in Northeast China during the heating period, but little information has been available. Aerosol particles were collected in winter at a site in a suburban county town (T1) and a site in a background rural area (T2). Morphology, size, elemental composition, and mixing state of individual aerosol particles were characterized by transmission electron microscopy (TEM). Aerosol particles were mainly composed of organic matter (OM) and S-rich and certain amounts of soot and K-rich. OM represented the most abundant particles, accounting for 60.7% and 53.5% at the T1 and T2 sites, respectively. Abundant spherical OM particles were likely emitted directly from coal-burning stoves. Soot decreased from 16.9% at the T1 site to 4.6% at the T2 site and sulfate particles decrease from 35.9% at the T2 site to 15.7% at the T1 site, suggesting that long-range transport air masses experienced more aging processes and produced more secondary particles. Based on our investigations, we proposed that emissions from coal-burning stoves in most rural areas of the west part of Northeast China can induce regional haze episodes. Full article
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Atmosphere, EISSN 2073-4433, Published by MDPI AG
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