LABORATORY AND FIELD INVESTIGATION OF MIXING, MORPHOLOGY AND OPTICAL PROPERTIES OF SOOT AND SECONDARY ORGANIC AEROSOLS PDF Download
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Languages : en
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Author:
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Languages : en
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Author:
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Languages : en
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Abstract : Soot particles form during incomplete combustion of carbonaceous materials. These particles strongly absorb light and directly affect Earth's climate by warming our atmosphere. When freshly emitted, soot particles have a fractal-like morphology consisting of aggregates of carbon spherules. During atmospheric processing, soot aggregates interact with other materials present in our atmosphere (i.e., other aerosol or condensable vapors) and these interactions can result in the formation of coated, mixed or compacted soot particles with different morphologies. Any process that alters the morphology (shape, size and internal structure) and mixing state of soot also affects its optical properties, which in turn affect the soot radiative forcing in the atmosphere. The complex morphology and internal mixing state of soot makes it difficult to estimate the soot's radiative properties. A detailed investigation of soot at the single particle level using electron microscopy, thus, becomes essential to provide accurate information for climate models, which generally assumes simple spherical morphologies. Tar balls are another type of carbonaceous aerosol, in the brown carbon family, commonly formed during smoldering combustion of biomass materials. Like soot, tar balls can also form aggregates. Tar balls aggregates have different optical properties from those of individual tar balls. During my doctorate studies, I made extensive use of electron microscopy and image analysis tools to investigate the morphology and mixing state of soot and tar balls collected during different laboratory and field studies. In one of my research projects, I explored the morphology of cloud processed soot. For this, I investigated the morphology of soot particles collected from the Po Valley in Italy where fog often forms, especially in winter. Our investigation showed that soot particles became compacted after fog processing. The compaction of soot was further corroborated by a laboratory study, in which cloud processing was carried out within the Michigan Technological University cloud chamber. In another research project, I studied the effects of thermodenuding on the morphology of soot. I investigated the morphology of five sets of soot samples of different sizes before xiii and after themodenuding. Our investigation showed no significant change in the morphology of soot by thermodenuding, a result that is important for those who attempt to measure the optical properties of internally mixed coated particles. In a third study, I used T-Matrix and Lorenz-Mie models to calculate the optical properties and then estimate the radiative forcing of tar ball aggregates and individual tar balls. In fact, in a recent publication, we reported a significant fraction of tar ball aggregates from different locations on Earth. My numerical calculations showed that the optical properties of tar ball aggregates are different from those of individual tar balls and are not always well approximated by Lorentz-Mie calculations. These findings highlight the necessity to account for the aggregation of tar balls in global models. My doctorate research provides detailed information on the morphology and mixing state of soot and tar ball aggregates. This information can be used to improve global climate models and reduce uncertainties in the radiative forcing of these aerosol particles.
Author: Swarup China
Publisher: MDPI
ISBN: 3038971332
Category : Science
Languages : en
Pages : 215
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This book is a printed edition of the Special Issue "Morphology and Internal Mixing of Atmospheric Particles" that was published in Atmosphere
Author: Dan Zhang
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Languages : en
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Soot particles released from fossil fuel combustion and biomass burning have a large impact on the regional/global climate by altering the atmospheric radiativeproperties and by serving as cloud condensation nuclei (CCN). However, the exact forcing is affected by the mixing of soot with other aerosol constituents, such as sulfuric acid. In this work, experimental studies have been carried out focusing on three integral parts: (1) heterogeneous uptake of sulfuric acid on soot; (2) hygroscopic growth of H2SO4-coated soot aerosols; (3) effect of H2SO4 coating on scattering and extinction properties of soot particles. A low-pressure laminar-flow reactor, coupled to ion drift chemical ionization mass spectrometry (ID-CIMS) detection, is used to study uptake coefficients of H2SO4 on combustion soot. The results suggest that uptake of H2SO4 takes place efficiently on soot particles, representing an important route to convert hydrophobic soot to hydrophilic aerosols. A tandem differential mobility analyzing (TDMA) system is employed to determine the hygroscopicity of freshly generated soot in the presence of H2SO4 coating. It is found that fresh soot particles are highly hydrophobic, while coating of H2SO4 significantly facilitates water uptake on soot even at sub-saturation relative humidities. The results indicate that aged soot particles in the atmosphere can potentially be an efficient source of CCN. Scattering and extinction coefficient measurements of the soot-H2SO4 mixed particles are conducted using a three wave length Nephelometer and a multi-path extinction cell. Coating of H2SO4 is found to increase the single scattering albedo (SSA) of soot particles which has impact on the aerosol direct radiative effect. Other laboratory techniques such as transmission electron microscopy (TEM) and Fourier transform infrared spectrometry (FTIR) are utilized to examine the morphology and chemical composition of the soot-H2SO4 particles. This work provides critical information concerning the heterogeneous interaction of soot and sulfuric acid, and how their mixing affects the hygroscopic and optical properties of soot. The results will improve our ability to model and assess the soot direct and indirect forcing and hence enhance our understanding of the impact of anthropogenic activities on the climate.
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Languages : en
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Soot particles are generated by incomplete combustion of fossil and biomass fuels. Through direct effects clear air aerosols containing black carbon (BC) such as soot aerosols, absorb incoming light heating the atmosphere, while most other aerosols scatter light and produce cooling. Even though BC represents only 1-2% of the total annual emissions of particulate mass to the atmosphere, it has been estimated that the direct radiative effect of BC is the second-most important contributor to global warming after absorption by CO2. Ongoing studies continue to underscore the climate forcing importance of black carbon. However, estimates of the radiative effects of black carbon on climate remain highly uncertain due to the complexity of particles containing black carbon. Quantitative measurement of BC is challenging because BC often occurs in highly non-spherical soot particles of complex morphology. Freshly emitted soot particles are typically fractal hydrophobic aggregates. The aggregates consist of black carbon spherules with diameters typically in the range of about 15-40 nm, and they are usually coated by adsorbed polyaromatic hydrocarbons (PAHs) produced during combustion. Diesel-generated soot particles are often emitted with an organic coating composed primarily of lubricating oil and unburned fuel, as well as well as PAH compounds. Sulfuric acid has also been detected in diesel and aircraft-emitted soot particles. In the course of aging, these particle coatings may be substantially altered by chemical reactions and/or the deposition of other materials. Such processes transform the optical and CCN properties of the soot aerosols in ways that are not yet well understood. Our work over the past seven years consisted of laboratory research, instrument development and characterization, and field studies with the central focus of improving our understanding of the black carbon aerosol climate impacts. During the sixth year as well as during this seventh year (no-cost extension period) of our grant, we extended our studies to perform experiments on the controlled production and characterization of secondary organic aerosol.
Author: Swarup China
Publisher:
ISBN:
Category : Atmospheric physics
Languages : en
Pages : 270
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We found that the morphology of fresh soot emitted by vehicles depends on the driving conditions (i.e.; the vehicle specific power). Soot emitted by biomass burning is often heavily coated by other materials while processing of soot in urban environment exhibits complex mixing. We also found that long-range transported soot over the ocean after atmospheric processing is very compacted. In addition, our results suggest that freezing process can facilitate restructuring of soot and results into collapsed soot. Furthermore, numerical simulations showed strong influence on optical properties when fresh open fractal-like soot evolved to collapsed soot. Further investigation of long-range transported aged particles exhibits that they are efficient in water uptake and can induce ice nucleation in colder temperature.
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Category :
Languages : en
Pages : 56
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Author: Sara Danielle Forestieri
Publisher:
ISBN: 9780355972436
Category :
Languages : en
Pages : 0
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Author: Huaxin Xue
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Category :
Languages : en
Pages :
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Soot aerosols are well known to be atmospheric constituents, but the hydrophobic nature of fresh soot likely prohibits them from encouraging cloud development. Soot aged through contact with oxygenated organic compounds may become hydrophilic enough to promote water uptake. In this study, the tandem differential mobility analyzer (TDMA) and differential mobility analyzer-aerosol particle mass analyzer (DMA-APM) were employed to measure the changes in morphology and hygroscopicity of soot aerosol particles upon coating with succinic and glutaric acids. The effective densities, fractal dimensions and dynamic shape factors of fresh and coated soot aerosol particles have been determined. Significant size-dependent increases of soot particle mobility diameter, mass, and effective density ([rho]eff) were observed upon coating of aggregates with succinic acid. These properties were restored back to their initial states once the acid was removed by heating, suggesting no restructuring of the soot core had occurred. Coating of soot with glutaric acid, on the other hand, leads to a strong size shrinking with a diameter growth factor ~0.60, even after the acid has been removed by heating suggesting the strong restructuring of the soot agglomerate. The additional 90% RH cycle can evidently enhance the restructuring process. The extinction and scattering properties at 532 nm of soot particles internally mixed with dicarboxylic acids were investigated experimentally using a cavity ring-down spectrometer and an integrating nephelometer, respectively, and the absorption is derived as the difference between extinction and scattering. It was found that the organic coatings significantly affect the optical and microphysical properties of the soot aggregates. The size-dependent amplification factors of light scattering were as much as 3.8 and 1.7 with glutaric and succinic acids coatings, respectively. Additional measurements with soot particles that are first coated with glutaric acid and then heated to remove the coating show that both scattering and absorption are enhanced by irreversible restructuring of soot aggregates to more compact globules. These results reveal the microphysical state of soot aerosol with incomplete restructuring in the atmosphere, and advance the treatment of atmospheric aged soot aerosol in the Mie theory shell-and-core model.
Author: Kristin Di Monte
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Languages : en
Pages : 0
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Light extinction by atmospheric aerosol particles and their interactions with water are heavily dependent on their chemical composition, morphology, and mixing state. Both properties are crucial for determining the impact aerosol particles have on our climate. Since light extinction directly impacts visibility as well as climate, measurements of the extinction at varying relative humidities (RH) are needed in order to improve climate models. In this work we have measured the relative humidity dependence of aerosol light extinction and water uptake at 643 nm for particles of varying ammonium sulfate/organic compositions. Internal as well as external mixtures of levoglucosan, sucrose, and adipic acid with ammonium sulfate are investigated using cavity ring-down spectroscopy (CRDS). Optical growth factor (fRH) and hygroscopicity parameters ([kappa]) are reported for each aerosol system.
