Investigation of the absorption Ångström exponent and its relation to physicochemical properties for mini-CAST soot

Török, Sandra; Malmborg, Vilhelm; Simonsson, Johan; Eriksson, Axel; Martinsson, Johan; Mannazhi, Manu; Pagels, Joakim; Bengtsson, Per Erik

doi:10.1080/02786826.2018.1457767

Cited by 46 publications

(30 citation statements)

References 38 publications

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“…Therefore, in contrast to the present study, small particles were always associated with a low EC content even at fuellean conditions. Török et al (2018) tuned the particle size (miniCAST 5201C) mostly by diluting propane with nitrogen at slightly fuel-rich conditions. The higher the dilution factor the smaller was the GMD (100-300 nm) and the higher the AAE (∼1-3.5) and OC/TC ratio (>10 to ∼50%) of the particles.…”

Section: Resultsmentioning

confidence: 99%

Characterization of a new miniCAST with diffusion flame and premixed flame options: Generation of particles with high EC content in the size range 30 nm to 200 nm

Ess

Vasilatou

2018

Aerosol Science and Technology

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Flame-generated soot from miniCAST burners is increasingly being used in academia and industry as engine exhaust soot surrogate for atmospheric studies and instrument calibration. Previous studies have found that elemental carbon (EC) content of miniCAST soot is proportional to the mean particle size. Here, the characterization of a prototype miniCAST generator (5201 Type BC), which was designed to decouple the soot composition from the particle size and produce soot particles with high EC and BC content in a large size range, is reported. This prototype may operate either in a diffusion-flame or a partially premixedflame mode, an option that was not available in former models. It was confirmed that soot properties, such as EC content and Ångström absorption exponent (AAE), were linked to the overall flame composition. In particular, combustion under fuel-rich conditions provided particles with size coupled to the EC fraction and AAE, i.e. smaller particles exhibited a lower EC fraction and higher AAE. In contrast, with fuel-lean diffusion flames and especially with premixed flames under near overall stoichiometric conditions small particles (down to 30 nm) with high EC/TC ratios (>60%) and low AAE (≈1.4) could be generated even without any thermal after-treatment. This new source might thus serve in the future as a useful surrogate for engine exhaust emissions and help to improve calibration procedures of common aerosol instruments.

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Section: Resultsmentioning

confidence: 99%

Characterization of a new miniCAST with diffusion flame and premixed flame options: Generation of particles with high EC content in the size range 30 nm to 200 nm

Ess

Vasilatou

2018

Aerosol Science and Technology

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“…It is known from basic combustion studies and model flames that soot properties change with decreasing combustion temperature. Non-regulated emissions with health impact such as aromatic compounds [39], including PAHs, may increase as combustion temperature decreases [40].…”

Section: Introductionmentioning

confidence: 99%

Effect of Renewable Fuels and Intake O2 Concentration on Diesel Engine Emission Characteristics and Reactive Oxygen Species (ROS) Formation

et al. 2020

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Renewable diesel fuels have the potential to reduce net CO2 emissions, and simultaneously decrease particulate matter (PM) emissions. This study characterized engine-out PM emissions and PM-induced reactive oxygen species (ROS) formation potential. Emissions from a modern heavy-duty diesel engine without external aftertreatment devices, and fueled with petroleum diesel, hydrotreated vegetable oil (HVO) or rapeseed methyl ester (RME) biodiesel were studied. Exhaust gas recirculation (EGR) allowed us to probe the effect of air intake O2 concentration, and thereby combustion temperature, on emissions and ROS formation potential. An increasing level of EGR (decreasing O2 concentration) resulted in a general increase of equivalent black carbon (eBC) emissions and decrease of NOx emissions. At a medium level of EGR (13% intake O2), eBC emissions were reduced for HVO and RME by 30 and 54% respectively compared to petroleum diesel. In general, substantially lower emissions of polycyclic aromatic hydrocarbons (PAHs), including nitro and oxy-PAHs, were observed for RME compared to both HVO and diesel. At low-temperature combustion (LTC, O2 < 10%), CO and hydrocarbon gas emissions increased and an increased fraction of refractory organic carbon and PAHs were found in the particle phase. These altered soot properties have implications for the design of aftertreatment systems and diesel PM measurements with optical techniques. The ROS formation potential per mass of particles increased with increasing engine O2 concentration intake. We hypothesize that this is because soot surface properties evolve with the combustion temperature and become more active as the soot matures into refractory BC, and secondly as the soot surface becomes altered by surface oxidation. At 13% intake O2, the ROS-producing ability was high and of similar magnitude per mass for all fuels. When normalizing by energy output, the lowered emissions for the renewable fuels led to a reduced ROS formation potential.

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“…In addition, Kahnert et al found that the homogeneous sphere model provided more accurate results than the layered sphere model. Similarly, Torok et al (2018) suggested that soot core and coating is not a good model for laboratory-produced soot. China et al (2015) investigated soot particles transported over long distances.…”

Section: Introductionmentioning

confidence: 99%

Mie Scattering Captures Observed Optical Properties of Ambient Biomass Burning Plumes Assuming Uniform Black, Brown, and Organic Carbon Mixtures

et al. 2019

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We use a simple model of a spherical biomass burning aerosol particle containing an internal mixture of black carbon (BC) and organic carbon (OC) with an effective refractive index calculated as a volume fraction‐weighted mean of refractive indices. Brown carbon (BrC) is considered to be an OC with an imaginary part of refractive index at the blue end of the solar spectrum higher (in absolute value) than at the red end. Mie‐scattering formalism is employed to calculate absorption Ångström exponent (AAE) as a function of single‐scattering albedo (SSA) for a set of BC refractive indices, BC volume fraction, and a set of effective refractive indices of BC and BrC mixtures. Ambient plumes are characterized by their mean SSA at 405 nm wavelength and two‐wavelength (405 and 781 nm) AAE values. Comparing observed and model‐calculated AAE and SSA values identifies the BC refractive index and its volume fraction and an effective refractive index of the BC and BrC mixture. From these values, the imaginary part of BrC refractive index is calculated. For observed southwestern ambient fires, the imaginary part of BrC refractive index is ≤0.016. In contrast, fires in the Amazon and from Africa are dominated by BC. We also use the Mie scattering model to establish the upper limit on AAE of BC (AAE ≤ 1.4) and the upper limit of the BC and OC mixture (AAE ≤ 1.7). Any AAE(405/781) > 1.7 requires the presence of BrC. We derive several relationships between AAE, SSA, BC fractions, and an imaginary part of BrC refractive index of ambient fires.

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Investigation of the absorption Ångström exponent and its relation to physicochemical properties for mini-CAST soot

Cited by 46 publications

References 38 publications

Characterization of a new miniCAST with diffusion flame and premixed flame options: Generation of particles with high EC content in the size range 30 nm to 200 nm

Characterization of a new miniCAST with diffusion flame and premixed flame options: Generation of particles with high EC content in the size range 30 nm to 200 nm

Effect of Renewable Fuels and Intake O2 Concentration on Diesel Engine Emission Characteristics and Reactive Oxygen Species (ROS) Formation

Mie Scattering Captures Observed Optical Properties of Ambient Biomass Burning Plumes Assuming Uniform Black, Brown, and Organic Carbon Mixtures

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