Una Trivanovic

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Trivanovic

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Una

ORCID

0000-0002-0748-017X

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Publications 1 - 10 of 11

Development and characterization of reference environmentally relevant micro-nano-plastics for risk assessment studies
Das, Milton; Calderon, Leonardo; Singh, Dilpreet; et al. (2025)
NanoImpact
Micro- and nano-plastics (MNPs) have become ubiquitous environmental pollutants. Extensive toxicological studies of MNPs have been conducted in recent years. However, because of the difficulties involved in extraction and collection of MNPs from environmental media, most of these studies have employed simplistic, pristine, spherical, micro- or nano-sized commercial MNPs, whose properties, including morphology, surface chemistry, and size, do not adequately approximate those of environmentally relevant MNPs. Here, we describe the development and use of methods for the synthesis of well characterized, environmentally relevant MNPs across the life cycle of a plastic material, in a property-controlled manner. Multiple degradation scenarios, including mechanical fragmentation (cryogenic milling), UV weathering, and thermal disintegration (incineration) were applied to virgin plastic materials (polyvinyl chloride, PVC; polyethylene terephthalate, PET; High density polyethylene, HDPE; Acrylonitrile butadiene styrene, ABS; polycarbonate, PC; and polypropylene, PP) to simulate the life cycle pathways that likely occur in the environment over time. The MNPs generated from these degradation processes were size fractionated using both “dry” and “wet” separation methods. Detailed physicochemical characterization of the size fractionated reference MNPs was performed to determine size, morphology, chemical and elemental compositions, and hydrophobicity. Microbiological sterility and endotoxin content of reference MNPs were also assessed. Protocols for storage of reference MNPs in controlled oxygen and moisture conditions for future use in toxicological studies are also described. The methodology developed in this study can be used to synthesize environmentally relevant reference MNPs across the life cycle of plastic materials for use in risk assessment studies.
Toward Elimination of Soot Emissions from Jet Fuel Combustion
Kelesidis, Georgios A.; Nagarkar, Amogh; Trivanovic, Una; et al. (2023)
Environmental Science & Technology
Soot from jet fuel combustion in aircraft engines contributes to global warming through the formation of contrail cirrus clouds that make up to 56% of the total radiative forcing from aviation. Here, the elimination of such emissions is explored through N2 injection (containing 0−25 vol % O2) at the exhaust of enclosed spray combustion of jet fuel that nicely emulates aircraft soot emissions. It is shown that injecting N2 containing 5 vol % of O2 enhances the formation of polyaromatic hydrocarbons (PAHs) that adsorb on the surface of soot. This increases soot number density and volume fraction by 25 and 80%, respectively. However, further increasing the O2 concentration to 20 or 25 vol % enhances oxidation and nearly eliminates soot emissions from jet fuel spray combustion, reducing the soot number density and volume fraction by 87.3 or 95.4 and 98.3 or 99.6%, respectively. So, a judicious injection of air just after the aircraft engine exhaust can drastically reduce soot emissions and halve the radiative forcing due to aviation, as shown by soot mobility, X-ray diffraction, Raman spectroscopy, nitrogen adsorption, microscopy, and thermogravimetric analysis (for the organic to total carbon ratio) measurements.
Dynamics of soot surface growth and agglomeration by enclosed spray combustion of jet fuel
Trivanovic, Una; Pereira Martins, Michael; Benz, Simon; et al. (2023)
Fuel
Morphology and size of soot from gas flares as a function of fuel and water addition
Trivanovic, Una; Sipkens, Timothy A.; Kazemimanesh, Mohsen; et al. (2020)
Fuel
A large-scale, laboratory turbulent diffusion flame was used to study the effects of fuel composition on soot size and morphology. The burner and fuels are typical of those used in the upstream oil and gas industry for gas flaring, a practice commonly used to dispose of excess gaseous hydrocarbons. Fuels were characterized by their carbon-to-hydrogen ratio (from 0.264 to 0.369) and their volumetric higher heating value (HHVv) (from 35.8 to 75.2 MJ/m3). Transmission electron microscopy (TEM) was used to assess primary particle and aggregate size, showing that the scaling of primary particle size to aggregate size was roughly the same for all of the considered fuels (dp = 16.3(da,100 [nm]/100)0.35). However, fuels with higher HHVv produced substantially larger soot aggregates. A scanning mobility particle sizer (SMPS) was also used (i) to measure mobility diameter distributions and (ii) in tandem with a centrifugal particle mass analyzer (CPMA) to determine the two-dimensional mass-mobility and effective density-mobility distributions using a new inversion approach. The new approach was shown to improve internal consistency of inferred morphological parameters, though with a shift relative to median-based analysis of the tandem data. Raman spectroscopy was used to quantify the degree of graphitization in the soot nanostructure. The addition of water to the fuel consistently reduced the soot yields but did not affect other morphological parameters. Larger aggregates also tended to have larger primary particles and higher Raman D/G ratios suggesting larger graphitic domains.
High-throughput generation of aircraft-like soot
Trivanovic, Una; Kelesidis, Georgios A.; Pratsinis, Sotiris E. (2022)
Aerosol Science and Technology
High-throughput, laboratory units for generation of aircraft-like soot are needed to quantify and understand the impact of such emissions on public health and climate change due to the high costs and limited access to aircraft engines. Enclosed spray combustion of jet fuel is used here to generate high soot concentrations, up to 255 mg/m3, three orders of magnitude higher than those typically obtained by widely used soot generators that use vapor-fed flames. This is attributed mostly to the use of real jet fuels. The large mass concentrations enable routine characterization of the soot specific surface area (SSA) and pore size distribution (PSD) by N2 adsorption. The geometric mean mobility diameter, overline(d)m, of soot agglomerates was systematically varied from 15 to 180 nm by varying the equivalence ratio (EQR) at constant fuel feed rates, while the organic to total carbon (OC/TC) ratio is low (<20%) at all conditions. The geometric mean primary particle (PP) diameter, overline(d)p, standard deviation, σ(g,p), and mass-mobility exponent, Dfm, were hardly altered in that EQR range. These measured D(fm) and σ(g,p) indicate that soot PPs were sinter-bonded by surface growth, in agreement with aircraft emissions literature. Most importantly, soot made at EQR ≤ 1.34 has mainly small pores (<2 nm) and similar morphology (D(fm) = 2.52 ± 0.17), SSA (160 − 239 m2/g), OC/TC (< 20%), overline(d)m (15 − 61 nm) and overline(d)p (14 nm) with those from high-thrust aircraft emissions.
Synthesis and dynamics of carbonaceous nanoparticles during enclosed spray combustion
Trivanovic, Una (2024)
Carbonaceous nanoparticles are both pollutants (soot) with negative effects on human health and the environment and valuable nanomaterials (carbon black). Understanding the processes which form such particles is therefore essential for designing combustion engines and reactors that minimize harmful emissions and enhance commercial profit. Aviation is a growing industry and an important source of soot. Soot from aviation tends to have a small size relative to other soot sources (e.g. diesel engines) which may result in greater health risks due to the higher toxicity of small particles. However, questions remain regarding the biological mechanisms tied to the negative health effects of soot. Similarly, aviation is unique in that it emits soot at high altitudes, where the particles may act as ice condensation nuclei forming contrails. These effects, however, are still poorly understood as experiments with real jet engines are costly and difficult to access. Low-cost and high-throughput methods for soot research are needed to better quantify the impact of soot on the climate, human health and to design improved engines. This way, trade-offs that minimize the impact of aviation on human health and the environment can be made. In this thesis, these challenges will be addressed through an overview of existing technologies, development of a laboratory soot generator and the application of this soot generator to better understand soot and NO emissions from jet fuel combustion. Chapter 1 gives an overview of existing strategies to reduce soot emission while considering industry requirements to limit pollutants such as CO2, carbon monoxide (CO), unburned hydrocarbons (UHC), oxides of nitrogen (NOx), and meeting strict safety and performance standards. Computational models are used to aid in aircraft engine design. However, models struggle to accurately capture the soot mobility diameter, dm, and volume fraction, fv, observed experimentally. Part of this discrepancy could be due to models’ oversimplification of the irregular morphology of soot and the current poor understanding of soot formation processes. Even so, aircraft combustors have been reducing soot emissions through extensive oxidation with the Rich-Quench-Lean (RQL) concept or by preventing soot formation with near-premixed, lean combustion such as in Lean Premixed Prevaporized (LPP) combustors. Near-premixed combustion prevents soot from forming in fuel-rich pockets while very lean combustion keeps temperatures low, thus preventing NOx formation. The use of alternative fuels could also reduce soot emissions. Sustainable Aviation Fuels (SAF) tend to have lower aromatic content compared to conventional jet fuels, which reduces the formation of soot particularly at low engine thrusts. The use of SAF is attractive logistically, as it can be a drop-in fuel requiring no new infrastructure or engines; however, the short-term supply is limited. In this regard, it is important that policies promote high blends of SAF which can reduce soot rather than adding a small amount of SAF to all flights, which has little to no impact on soot emissions. Chapter 2 describes the development of a low-cost, laboratory burner to produce aircraft-like soot from real jet fuels with high throughput. Laboratory burners are essential for facilitating research on soot emissions in a lower-cost and more controlled environment compared to a real aircraft engine. However, existing commercial soot generators fail to produce soot similar to that produced by aircrafts at high thrust. High-thrust aircraft soot tends to have Organic Carbon to Total Carbon (OC/TC) ratios < 25 % and small median mobility diameters, dm, in the range of 11 – 61 nm. Here, enclosed spray combustion (ESC) of jet A1 fuel is used to produce soot with similar OC/TC, dm and primary particle diameter, dp, to that observed in soot from real aircraft. Specifically, OC/TC ratios were consistently < 20% while the median dm ranged from 15 – 150 nm depending on the Effective eQuivalence Ratio (EQR) employed. Soot particles produced at the low end of this range (dm < 50 nm) can be considered ‘aircraft-like’. The specific surface area (SSA) was quantified for the first time for aircraft-like particles (160 – 239 m2/g) with mainly small pores (< 2 nm). ESC therefore provides a new, lab-based method to replicate soot produced by aircrafts at high thrust. Chapter 3 explores the formation and growth dynamics of soot produced by the ESC burner developed in Chapter 2 at various EQR. This characterization and modeling of the formation and growth of soot during spray combustion of jet fuel can be used to improve the understanding and modeling of soot from aircraft engines. The centerline flame temperature peaked at Heights Above the Burner (HAB) = 5 – 10 cm then dropped continuously through to the end of the enclosure at HAB = 63 cm. The maximum temperature depended on the EQR with lower EQR (closer to stoichiometric) resulting in higher temperatures than the richer flames. Within a flame, the dm of soot grew continuously from HAB = 5 to 63 cm while the dp was approximately constant at all points along the enclosure. Discrete Element Modeling (DEM) revealed that this behavior is attributable to the leveling off of soot surface growth after short residence times, before HAB = 5 cm and agglomeration then took over as the primary mechanism for particle growth. At low EQR = 1.46, the dp leveled off at approximately 14 nm. At higher EQR (e.g. 1.88) soot surface growth was enhanced leading to larger dp, up to 23 nm. Across the same range, the Raman D/G ratio dropped from 0.9 to 0.8 at EQR = 1.46 and 1.88, respectively, while the crystallite length increased from 1.24 to 1.47 nm. These correlations suggests that high EQR produced larger dp with more graphitic, crystalline particles compared to the smaller more disordered primary particles produced at low EQR. Chapter 4 investigates the trade-off between soot and nitric oxide (NO) during ESC of jet fuel as combustion conditions that reduce soot emissions tend to increase NOx, making it difficult to reduce both pollutants at the same time. Judicious swirl-injection of air downstream of ESC can drastically reduce soot emissions through oxidation. However, this swirl-injection strategy leads to higher temperatures that promote NO. Early injection of air results in the lowest soot emissions, but the highest NO, nearly triple that produced when air is injected far downstream of the burner. Conversely, late injection of air does not reduce soot emissions although NO remained low. Here, a quantitative correlation is found between injection location, temperature, soot and NO. Therefore, the combustion conditions which allowed for a balanced trade-off between NO and soot emissions was found and on par with or lower than the lowest NOx emissions per unit mass of fuel from in-service aircraft engines. Enclosed spray combustion of jet fuel provides a high-throughput method for producing soot with comparable morphology and composition to that from aircraft at high thrust for the first time. The understanding of soot formation and growth during ESC of jet fuel can help to improve modeling and design of aircraft engines through an improved fundamental understanding of the processes involved. Furthermore, quantifying the trade-off between soot and NO emissions is essential for developing engines which minimize both pollutants. In the future, ESC could be used for calibrating regulatory instrumentation, testing novel jet fuels or production of sufficiently large quantities for further research on the biological effects of soot.
Highlights of Analytical Sciences in Switzerland Division of Analytical Sciences A Division of the Swiss Chemical Society
Kelesidis, Georgios A.; Nagarkar, Amogh; Trivanovic, Una; et al. (2024)
Chimia
Dispersion and Dosimetric Challenges of Hydrophobic Carbon-Based Nanoparticles in In Vitro Cellular Studies
Lizonova, Denisa; Trivanovic, Una; Demokritou, Philip; et al. (2024)
Nanomaterials
Methodologies across the dispersion preparation, characterization, and cellular dosimetry of hydrophilic nanoparticles (NPs) have been developed and used extensively in the field of nanotoxicology. However, hydrophobic NPs pose a challenge for dispersion in aqueous culture media using conventional methods that include sonication followed by mixing in the culture medium of interest and cellular dosimetry. In this study, a robust methodology for the preparation of stable dispersions of hydrophobic NPs for cellular studies is developed by introducing continuous energy over time via stirring in the culture medium followed by dispersion characterization and cellular dosimetry. The stirring energy and the presence of proteins in the culture medium result in the formation of a protein corona around the NPs, stabilizing their dispersion, which can be used for in vitro cellular studies. The identification of the optimal stirring time is crucial for achieving dispersion and stability. This is assessed through a comprehensive stability testing protocol employing dynamic light scattering to evaluate the particle size distribution stability and polydispersity. Additionally, the effective density of the NPs is obtained for the stable NP dispersions using the volumetric centrifugation method, while cellular dosimetry calculations are done using available cellular computational modeling, mirroring approaches used for hydrophilic NPs. The robustness of the proposed dispersion approach is showcased using a highly hydrophobic NP model (black carbon NPs) and two culture media, RPMI medium and SABM, that are widely used in cellular studies. The proposed approach for the dispersion of hydrophobic NPs results in stable dispersions in both culture media used here. The NP effective density of 1.03–1.07 g/cm³ measured here for black carbon NPs is close to the culture media density, resulting in slow deposition on the cells over time. So, the present methodology for dispersion and dosimetry of hydrophobic NPs is essential for the design of dose–response studies and overcoming the challenges imposed by slow particle deposition.
Opinion: Eliminating aircraft soot emissions
Trivanovic, Una; Pratsinis, Sotiris E. (2023)
Aerosol Research Discussion
Soot from aircraft engines deteriorates air quality around airports and can contribute to climate change primarily by influencing cloud processes and contrail formation. Simultaneously, aircraft engines emit CO2, nitrogen oxides (NOx) and other pollutants which also negatively affect human health and the environment. While urgent action is needed to reduce all pollutants, strategies to reduce one pollutant may increase another, calling for a need to decrease, for example, the uncertainty associated with soot’s contribution to net Radiative Forcing (RF) in order to design targeted policies that minimize the formation and release of all pollutants. Aircraft soot is characterized by rather small median mobility diameters, dm = 8 – 60 nm, and at high thrust, low (< 25 %) organic carbon to total carbon (OC/TC) ratios while at low thrust the OC/TC can be quite high. Computational models could aid in the design of new aircraft combustors to reduce emissions, but current models struggle to capture the soot dm, and volume fraction, fv measured experimentally. This may be in part due to oversimplification of soot’s irregular morphology in models and a still poor understanding of soot inception. Nonetheless, combustor design can significantly reduce soot emissions through extensive oxidation or near-premixed, lean combustion. For example, lean premixed prevaporized combustors significantly reduce emissions at high thrust by allowing injected fuel to fully vaporize before ignition while low temperatures from very lean jet fuel combustion limit the formation of NOx. Alternative fuels can be used alongside improved combustor technologies to reduce soot emissions. However, current policies and low supply promote the blending of alternative fuels at low ratios (~1 %) for all flights, rather than using high ratios (> 30 %) in a few flights which could meaningfully reduce soot emissions. Here, existing technologies for reducing such emissions through combustor and fuel design will be reviewed to identify strategies that eliminate them.
Trade-off between soot and NO emissions during enclosed spray combustion of jet fuel
Trivanovic, Una; Pratsinis, Sotiris E. (2024)
Scientific Reports
Aviation emissions of soot and nitrogen oxides are strictly regulated as they adversely impact human health and the environment. Jet fuel combustion conditions that decrease one pollutant concentration increase the other. Although it is not impossible to achieve both low soot and NOx through clever design, it is hard to simultaneously reduce both. Although it is difficult to study such conditions due to high temperatures and gas flowrates of aircraft engines, recently it was shown that Enclosed Spray Combustion (ESC) of jet fuel results in soot with similar characteristics to that from aircrafts making ESC an attractive unit for studying aviation-like emissions. Furthermore, judicious swirl-injection of air downstream of the ESC burner drastically reduces soot emissions. Here the trade-off between NO and soot emissions during combustion of jet fuel is studied for the first time, to the best of our knowledge, accounting for the detailed structure of soot. Injecting air shortly after the ESC burner decreases soot but increases NO emissions, while such injection further downstream has the inverse outcome. This interplay between soot and NO emissions was correlated quantitatively with the gas temperature shortly after air injection. Consequently, combustion conditions for an optimal trade-off between soot and NO emissions for the ESC conditions studied here are identified that are at or below the lowest NOx emissions per unit mass of fuel from existing aircraft engines.

Publications 1 - 10 of 11

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