Fresh Soot Particles Research Articles

On the correlation between hygroscopic properties and chemical composition of cloud condensation nuclei obtained from the chemical aging of soot particles with O3 and SO2

Soot particles released in the atmosphere have long been investigated for their ability to affect the radiative forcing. Although freshly emitted soot particles are generally considered to yield only positive contributions to the radiative forcing, atmospheric aging can activate them into efficient cloud condensation or ice nuclei, which can trigger the formation of persistent clouds and ultimately provide a negative contribution to the radiative forcing. Depending on their residence time in the atmosphere, soot particles can undergo several physical and chemical aging processes that affect their chemical composition, particle size distribution and morphology, and ultimately their optical and hygroscopic properties. The impact of the physical-chemical aging on the properties of soot particles is still difficult to quantify, as well as their effect on the radiative forcing of the atmosphere.This work investigates the hygroscopic properties of chemically aged soot particles obtained from the combustion of aviation fuel, and in particular the interplay between aging mechanisms initiated by two widespread atmospheric oxidizers (O3 and SO2). Activation is measured in water supersaturation conditions using a cloud condensation nuclei counter. Once particle morphology and size distribution are taken into account, the hygroscopicity parameter κ is derived using κ-Köhler theory and correlated to the change of the chemical composition of the particles aged in a simulation chamber. While fresh soot particles are poor cloud condensation nuclei (κ < 10−4) and are not significantly affected by either O3 or SO2 at the timescale of the experiments, rapid activation is observed when they are simultaneously exposed to both oxidizers. Activated particles become efficient cloud condensation nuclei, comparable to the highly hygroscopic particulate matter typically found in the atmosphere (κ = 0.2–0.6 at RH = 20 %). Statistical analysis reveals a correlation between the activation and sulfur-containing ions detected on the chemically aged particles that are absent from the fresh particles.

Characterisation of a self-sustained, water-based condensation particle counter for aircraft cruising pressure level operation

Abstract. Aerosol particle number concentration measurements are a crucial part of aerosol research. Vertical profile measurements and high-altitude/low-pressure performance of the respective instruments become more important for remote sensing validation and a vital tool for the observation of climate variables. This study tests the new, commercially available water condensation particle counter (MAGIC 210-LP) for the deployment at aircraft cruising pressure levels that the European research infrastructure IAGOS (In-service Aircraft for a Global Observing System; http://www.iagos.org, last access: 2 May 2023) is aiming for by operating measurement instrumentation onboard passenger aircraft. We conducted laboratory experiments for conditions to simulate passenger aircraft flight altitude at operation pressure. We demonstrate that this type of water condensation particle counter shows excellent agreement with a butanol-based instrument used in parallel. A Faraday cup aerosol electrometer serves as the reference instrument. Experiments are performed with test aerosol ammonium sulfate and fresh combustion soot at pressure levels ranging from 700 to 200 hPa. For soluble particles like ammonium sulfate, the 50 % detection efficiency cut-off diameter (D50) is around 5 nm and does not differ significantly for all performed experiments. For non-soluble fresh soot particles, the D50 cut-off diameter of approximately 10 nm does not vary substantially as a function of pressure, whereas the 90 % detection efficiency cut-off diameter D90 increases from 19 nm at 700 hPa to 37 nm at 200 hPa. The overall counting efficiency for particles larger than 40 nm reaches 100 % for working pressures of 200 hPa and higher.

75 Effect of Atmospheric Aging on Soot Particle Toxicity in Airway Epithelial-Endothelial Co-Culture Models at the Air–Liquid Interface

Abstract Secondary organic aerosols (SOAs) formed from anthropogenic or biogenic volatile precursors in the atmosphere substantially contribute to the ambient fine particulate matter (PM2.5) burden, which has been associated with adverse human health effects. However, there is only limited evidence of their differential toxicological impact. To study those effects, we generated different aerosols by atmospheric aging of volatile biogenic (β-pinene) or anthropogenic (naphthalene) precursors of SOA that condensed on soot particles (SPs). In-depth, physicochemical aerosol characterization revealed very similar physical properties for SOAβPIN-SP and SOANAP-SP, but distinct differences in chemical composition. For example, SOANAP-SP was associated with the formation of more oxidized and more aromatic SOAs with a higher oxidative potential compared to β-pinene. By exposing a co-culture model system consisting of lung epithelial cells (A549) and endothelial cells (EA.hy926) at the air-liquid interface to different aerosol concentrations, we aimed to discriminate toxicological effects. Integrated transcriptomic and metabolomics analysis revealed induction of stress-related airways remodeling and an early type I immune response, for the A549 cells, especially after the exposure to SOANAP-SP. The underlying EA.hy926 cells showed similar transcriptomic changes in early response genes and genes related to cardiovascular pathologies after exposure to both SOA types, however to a greater extent after SOANAP-SP. While fresh SP without coating by SOA evinced only minor changes in both cell lines. Altogether, this supports the assumption of a pivotal role of atmospheric chemistry and the chemical PM composition on the toxicological outcomes and highlights the importance of organic compounds on cellular effects.

Enhanced soot particle ice nucleation ability induced by aggregate compaction and densification

Abstract. Soot particles, acting as ice nucleating particles (INPs), can contribute to cirrus cloud formation, which has an important influence on climate. Aviation activities emitting soot particles into the upper troposphere can potentially impact ice nucleation (IN) in cirrus clouds. Pore condensation and freezing (PCF) is an important ice formation pathway for soot particles in the cirrus regime, which requires the soot INP to have specific morphological properties, i.e., mesopore structures. In this study, the morphology and pore size distribution of two kinds of soot samples were modified by a physical agitation method without any chemical modification by which more compacted soot sample aggregates could be produced compared to the unmodified sample. The IN activities of both fresh and compacted soot particles with different sizes, 60, 100, 200 and 400 nm, were systematically tested by the Horizontal Ice Nucleation Chamber (HINC) under mixed-phase and cirrus-cloud-relevant temperatures (T). Our results show that soot particles are unable to form ice crystals at T&gt;235 K (homogeneous nucleation temperature, HNT), but IN is observed for compacted and larger-sized soot aggregates (&gt;200 nm) well below the homogeneous freezing relative humidity (RHhom) for T&lt; HNT, demonstrating PCF as the dominating mechanism for soot IN. We also observed that mechanically compacted soot particles can reach a higher particle activation fraction (AF) value for the same T and RH condition compared to the same aggregate size fresh soot particles. The results also reveal a clear size dependence for the IN activity of soot particles with the same degree of compaction, showing that compacted soot particles with large sizes (200 and 400 nm) are more active INPs and can convey the single importance of soot aggregate morphology for the IN ability. In order to understand the role of soot aggregate morphology for its IN activity, both fresh and compacted soot samples were characterized systematically using particle mass and size measurements, comparisons from TEM (transmission electron microscopy) images, soot porosity characteristics from argon (Ar) and nitrogen (N2) physisorption measurements, as well as soot–water interaction results from DVS (dynamic vapor sorption) measurements. Considering the soot particle physical properties along with its IN activities, the enhanced IN abilities of compacted soot particles are attributed to decreasing mesopore width and increasing mesopore occurrence probability due to the compaction process.

Light scattering matrix for soot aerosol: Comparisons between experimental measurements and numerical simulations

Fractal aggregate model has shown significant superiority in simulating integral optical properties (like optical cross sections etc.) of soot aerosol. In this study, angular distributions of scattering matrices for soot samples were measured at 532 nm wavelength. Experiments were conducted over scattering angles from 5° to 175° using an improved and validated apparatus. Soot particles emitted from burning of toluene and n-heptane were collected and re-aerosolized for matrix measurements. Electrical mobility diameter distributions of soot aggregates were measured and converted to volume equivalent diameter distributions according to various conversion factors. Size distributions of soot monomers and fractal parameters were obtained through statistical analyses of transmission electron microscope (TEM) images. Fractal aggregate models were generated by a tunable particle-cluster algorithm, using measured size distributions of aggregates and statistically obtained morphological parameters. Multiple sphere T-matrix (MSTM) method was employed for the calculation of individual particles, and bulk scattering matrices were integrated from particles with same morphology parameters. Results indicated that measured scattering matrices for these two soot samples show similar angular behaviors. Compared with fresh soot particles, the collection and re-aerosolization treatments lead to larger mobility diameters and more compact particle structures. Fractal parameter, conversion factor, refractive index and polydisperse monomer all have various effects on different matrix elements. Inter-comparisons between simulations and measurements focus more on the performance of ideal fractal model consisting of point-contact monomers in simulating measured scattering matrices, and there is no doubt that ideal fractal aggregates cannot simultaneously reproduce measured angular distributions of all matrix elements.

Modelling the Optical Properties of Soot Particles under Various Aging Conditions

As atmospheric fresh soot particles age, they become coated with other chemical species. This transforms their physicochemical properties and affects their optical characteristics, which is of great importance to air quality, the environment and climate change. One of the predominantly occurring states of soot particles in the ambient environment is the core-shell mixing state. In this study, we used the core-shell model to calculate the optical absorption, scattering and extinction efficiency, absorption proportion and absorption exponent of coated soot particles. We then investigated the effects of different core sizes (D0), incident wavelengths (λ), coating materials and coating thicknesses on these optical characteristics. Absorption efficiency and absorption proportion of soot particles decreased as the coating became thicker, at core sizes of D0 = 20, 50 and 100 nm and λ = 405, 532 and 781 nm, regardless of the type of coating material. As the coating thickness increased, the absorption exponent (β) of inorganic-coated soot particles tended to rise and then fall, while the β value of organic-coated soot particles kept increasing. Our results advance our scientific understanding of the interaction of optical properties with chemical composition, mixing state, and aging processes of soot particles in the atmosphere.

Collection of soot particles into aqueous suspension using a particle-into-liquid sampler.

Steam collection devices collecting aerosol particles into liquid samples are frequently used to analyze water-soluble particulate material. The fate of water-insoluble components is often neglected. In this work, we show that fresh soot particles can be suspended into pure water using a steam collection device, the particle-into-liquid sampler (PILS, Weber et al. 2001). The overall collection efficiency of freshly generated soot particles was found to be on the order of 20%. This shows that, depending on the analytic technique employed, the presence of insoluble, and/or hydrophobic particles in liquid samples from steam collection cannot be neglected.Copyright © 2018 The Author(s). Published with license by Taylor & Francis Group, LLC

Morphological transformation of soot: investigation of microphysical processes during the condensation of sulfuric acid and limonene ozonolysis product vapors

Abstract. The morphological transformation of soot particles via condensation of low-volatility materials constitutes a dominant atmospheric process with serious implications for the optical and hygroscopic properties, as well as atmospheric lifetime of the soot. We consider the morphological transformation of soot aggregates under the influence of condensation of vapors of sulfuric acid, and/or limonene ozonolysis products. This influence was systematically investigated using a Differential Mobility Analyzer coupled with an Aerosol Particle Mass Analyzer (DMA–APM) and the Tandem DMA techniques integrated with a laminar flow-tube system. We hypothesize that the morphology transformation of soot results (in general) from a two-step process, i.e., (i) filling of void space within the aggregate and (ii) growth of the particle diameter. Initially, the transformation was dominated by the filling process followed by growth, which led to the accumulation of sufficient material that exerted surface forces, which eventually facilitated further filling. The filling of void space was constrained by the initial morphology of the fresh soot as well as the nature and the amount of condensed material. This process continued in several sequential steps until all void space within the soot aggregate was filled. And then “growth” of a spherical particle continued as long as vapors condensed on it. We developed a framework for quantifying the microphysical transformation of soot upon the condensation of various materials. This framework used experimental data and the hypothesis of “ideal sphere growth” and void filling to quantify the distribution of condensed materials in the complementary filling and growth processes. Using this framework, we quantified the percentage of material consumed by these processes at each step of the transformation. For the largest coating experiments, 6, 10, 24, and 58 % of condensed material went to filling process, while 94, 90, 76, and 42 % of condensed material went to growth process for 75, 100, 150, and 200 nm soot particles, respectively. We also used the framework to estimate the fraction of internal voids and open voids. This information was then used to estimate the volume-equivalent diameter of the soot aggregate containing internal voids and to calculate the dynamic shape factor, accounting for internal voids. The dynamic shape factor estimated based on the traditional assumption (of no internal voids) differed significantly from the value obtained in this study. Internal voids are accounted for in the experimentally derived dynamic shape factor determined in the present study. In fact, the dynamic shape factor adjusted for internal voids was close to 1 for the fresh soot particles considered in this study, indicating the particles were largely spherical. The effective density was strongly correlated with the morphological transformation responses to the condensed material on the soot particle, and the resultant effective density was determined by the (i) nature of the condensed material and (ii) morphology and size of the fresh soot. In this work we quantitatively tracked in situ microphysical changes in soot morphology, providing details of both fresh and coated soot particles at each step of the transformation. This framework can be applied to model development with significant implications for quantifying the morphological transformation (from the viewpoint of hygroscopic and optical properties) of soot in the atmosphere.

Internally Mixed Sea Salt, Soot, and Sulfates at Macao, a Coastal City in South China

ABSTRACT Direct observation of the mixing state of aerosol particles in a coastal urban city is critical to understand atmospheric processing and hygroscopic growth in humid air. Morphology, composition, and mixing state of individual aerosol particles from Macao, located south of the Pearl River Delta (PRD) and 100 km west of Hong Kong, were investigated using scanning electron microscopy (SEM) and transmission electron microscopy coupled with energy-dispersive X-ray spectrometry (TEM/EDX). SEM images show that soot and roughly spherical particles are prevalent in the samples. Based on the compositions of individual aerosol particles, aerosol particles with roughly spherical shape are classified into coarse Na-rich and fine S-rich particles. TEM/EDX indicates that each Na-rich particle consists of a Na-S core and NaNO3 shell. Even in the absence of heavy pollution, the marine sea salt particles were completely depleted in chloride, and Na-related sulfates and nitrates were enriched in Macao air. The reason could be that SO2 from the polluted PRD and ships in the South China Sea and NO2 from vehicles in the city sped up the chlorine depletion in sea salt through heterogeneous reactions. Fresh soot particles from vehicular emissions mainly occur near curbside. However, there are many aged soot particles in the sampling site surrounded by main roads 200 to 400 m away, suggesting that the fresh soot likely underwent a quick aging. Overall, secondary nitrates and sulfates internally mixed with soot and sea salt particles can totally change their surface hygroscopicity in coastal cities. IMPLICATIONS This study of compositional changes in mixed marine aerosols and anthropogenic pollutants underscores the importance of aerosol mixing states with regard to their role in visibility, climate, as well as health inhalation. Almost all sea salt particles in Macao air were depleted in chloride but enriched in Na-related sulfates and nitrates through heterogeneous atmospheric reactions. Most soot particles are aggregated with or encapsulated by S-rich particles, suggesting that the fresh soot particles likely underwent a quick aging. Future climate model should consider the mixing states of sea salt and soot particles in the atmosphere of the China coast.

Aged status of soot particles during the passage of a weak cyclone in Beijing

Atmospheric particles at an urban site in Beijing from Apr. 18 to 21, 2009, when a weak synoptic cyclone passed and the air quality was relatively fine, were investigated by using electron microscopes. Particles collected from different stages of the cyclone were characterized by their shape, size and elemental composition. Soot particles were predominant and concentrated in the size range of 0.2–1.0 μm, and out of this range were rarely detected. Most of the soot particles exhibited aged shape, i.e. shrunk clusters with liquid coating (the so-called core-shell structure), compared to the open spherule’s chain or agglomerate shape of fresh soot particles. Morphologies of the particles in the prefrontal and postfrontal air were compared. The mean equivalent diameter of the particles in the prefrontal air was 0.36–0.38 μm and in the postfrontal air was 0.35–0.41 μm. More than 50% of the particles had aspect ratios between 1.0 and 1.4, and the remains frequently smaller than 2.0. In terms of circularity factor, 57–64% particles in the prefrontal air and 41–51% in the postfrontal air appeared in the range of 0.6–1.0. These results indicate that the aged status of soot particles in the prefrontal and postfrontal air were not very different, although the quality of the postfrontal air was much better than that of the prefrontal air, suggesting that fresh soot particles in chain or aggregate shape could be modified into core-shell structure rapidly even in less polluted air. In addition, a primary estimate showed that aging had caused the decrease of the cross-section areas of soot parts in the particles. ► Soot particles during a cyclone passage in Beijing were studied. ► Aged status of soot in prefrontal and postfrontal air was not very different. ► Fresh soot particles could be modified rapidly in less polluted postfrontal air. ► Aging caused the decrease of cross-section areas of soot parts in the particles.

Characterization of the Single Particle Mixing State of Individual Ship Plume Events Measured at the Port of Los Angeles

Ship emissions contribute significantly to gaseous and particulate pollution worldwide. To better understand the impact of ship emissions on air quality, measurements of the size-resolved chemistry of individual particles in ship emissions were made at the Port of Los Angeles using real-time, single-particle mass spectrometry. Ship plumes were identified through a combination of ship position information and measurements of gases and aerosol particles at a site 500 m from the center of the main shipping channel at the Port of Los Angeles. Single particles containing mixtures of organic carbon, vanadium, and sulfate (OC-V-sulfate) resulted from residual fuel combustion (i.e., bunker fuel), whereas high quantities of fresh soot particles (when OC-V-sulfate particles were not present) represented distinct markers for plumes from distillate fuel combustion (i.e., diesel fuel) from ships as well as trucks in the port area. DC-V-sulfate particles from residual fuel combustion contained significantly higher levels of sulfate and sulfuric acid than plume particles containing no vanadium. These associations may be due to vanadium (or other metals such as iron) in the fuel catalyzing the oxidation of S0(2) to produce sulfate and sulfuric acid on these particles. Enhanced sulfate production on OC-V-sulfate ship emission particles would help explain some of the higher than expected sulfate levels measured in California compared to models based on emissions inventories and typical sulfate production pathways. Understanding the overall impact of ships emissions is critical for controlling regional air quality in the many populated coastal regions of the world.

Morphological and Elemental Classification of Freshly Emitted Soot Particles and Atmospheric Ultrafine Particles using the TEM/EDS

The Transmission Electron Microscopy (TEM) and Energy Dispersive Spectroscopy (EDS) were used to determine morphology and elemental composition of a variety of freshly emitted soot particles (acetylene flame, candle flame, kerosene flame, diesel exhaust, electric arc, plastic burning, styrofoam burning, wood burning [white oak and pine bark], and rice straw burning), which can be possible candidate soot in the ambient atmosphere, and ultrafine particles sampled in urban, industrial, and coastal sites during ultrafine particle formation events (combustion and photochemical events). By using mobility-classified non-refractory ((NH 4 ) 2 SO 4 ) and refractory (Polystyrene latex (PSL) and salt (NaCl)) particles, limitation of the TEM was tested. Data showed that the TEM method can be used to examine shapes of both volatile particles such as (NH 4 ) 2 SO 4 (100 nm) at low, but not high magnification (refer to low and high beam intensity, respectively), and non-volatile particles like NaCl (100 nm) and PSL (84 nm) at either low or high magnification. Distinct differences in morphological properties such as primary particle diameter, fractal dimension, and microstructure were observed among the different types of fresh soot particles. The atmospheric ultrafine particles were classified as agglomerates, sulfate mixtures (spherical), metallic oxides (spherical and polygonal), C-rich refractory (not agglomerated), C-rich non-refractory (not agglomerated), Si-rich (spherical), Na-rich (porous), or P-containing (non-spherical) particles. At the urban Gwangju site, a higher fraction of fresh and aged agglomerates was observed than at other sites. The C-rich non-refractory and sulfate mixtures were often observed in the photochemical event. The C-rich refractory particles were abundant at the Gwangju and Yeosu sites. The coastal Taean site had few agglomerates due to limited anthropogenic combustion source.