Lagrangian Simulations Research Articles

Euclid preparation

The Euclid mission, designed to map the geometry of the dark Universe, presents an unprecedented opportunity for advancing our understanding of the cosmos through its photometric galaxy cluster survey. Central to this endeavor is the accurate calibration of the mass- and redshift-dependent halo bias (HB), which is the focus of this paper. Our aim is to enhance the precision of HB predictions, which is crucial for deriving cosmological constraints from the clustering of galaxy clusters. Our study is based on the peak-background split (PBS) model linked to the halo mass function (HMF), and it extends it with a parametric correction to precisely align with results from an extended set of N-body simulations carried out with the OpenGADGET3 code. Employing simulations with fixed and paired initial conditions, we meticulously analyzed the matter-halo cross-spectrum and modeled its covariance using a large number of mock catalogs generated with Lagrangian perturbation theory simulations with the PINOCCHIO code. This ensures a comprehensive understanding of the uncertainties in our HB calibration. Our findings indicate that the calibrated HB model is remarkably resilient against changes in cosmological parameters, including those involving massive neutrinos. The robustness and adaptability of our calibrated HB model provide an important contribution to the cosmological exploitation of the cluster surveys to be provided by the Euclid mission. This study highlights the necessity of continuously refining the calibration of cosmological tools such as the HB to match the advancing quality of observational data. As we project the impact of our calibrated model on cosmological constraints, we find that given the sensitivity of the Euclid survey, a miscalibration of the HB could introduce biases in cluster cosmology analysis. Our work fills this critical gap, ensuring the HB calibration matches the expected precision of the Euclid survey.

Larval Transport Pathways for Lutjanus peru and Lutjanus argentiventris in the Northwestern Mexico and Tropical Eastern Pacific

Understanding how ocean currents influence larval dispersal and measuring its magnitude is critical for conservation and sustainable exploitation, especially in the Tropical Eastern Pacific (TEP), where the larval transport of rocky reef fish remains untested. For this reason, a lagrangian simulation model was implemented to estimate larval transport pathways in Northwestern Mexico and TEP. Particle trajectories were simulated with data from the Hybrid Ocean Coordinate Model, focusing on three simulation scenarios: (1) using the occurrence records of Lutjanus peru and L. argentiventris as release sites; (2) considering a continuous distribution along the study area, and (3) taking the reproduction seasonality into account in both species. It was found that the continuous distribution scenario largely explained the genetic structure previously found in both species (genetic brakes between central and southern Mexico and Central America), confirming that the ocean currents play a significant role as predictors of genetic differentiation and gene flow in Northwestern Mexico and the TEP. Due to the oceanography of the area, the southern localities supply larvae from the northern localities; therefore, disturbances in any southern localities could affect the surrounding areas and have impacts that spread beyond their political boundaries.

Radiocarbon as a tracer of the fossil fraction of regional carbon monoxide emissions

Abstract Carbon monoxide (CO) is an atmospheric pollutant with a positive net warming effect on the climate. The magnitude of CO sources and the fraction of fossil vs biogenic sources are still uncertain and vary across emissions inventories. Measurements of radiocarbon (14C) in CO could potentially be used to investigate the sources of CO on a regional scale because fossil sources lack 14C and reduce the 14C/C ratio (Δ14C) of atmospheric CO more than biogenic sources. We use regional Lagrangian model simulations to investigate the utility of Δ14CO measurements for estimating the fossil fraction of CO emissions and evaluating bottom-up emissions estimates (United Kingdom Greenhouse Gas, UKGHG, and TNO Copernicus Atmosphere Monitoring Service, TNO) in London, UK. Due to the high Δ14CO in atmospheric CO from cosmogenic production, both fossil and biogenic CO emissions cause large reductions in Δ14CO regionally, with larger reductions for fossil than biogenic CO per ppb added. There is a strong seasonal variation in Δ14CO in background air and in the sensitivity of Δ14CO to fossil and biogenic emissions of CO. In the UK, the CO emissions estimate from TNO has a higher fraction from fossil fuels than UKGHG (72\% vs 67\%). This results in larger simulated decreases in Δ14C per ppb CO for TNO emissions. The simulated differences between UKGHG and TNO are likely to be easily detectable by current measurement precision, suggesting that Δ14CO measurements could be an effective tool to understand regional CO sources and assess bottom-up emissions estimates.

Attribution of Excess Methane Emissions Over Marine Environments of the Mediterranean and Arabian Peninsula

AbstractTo accurately assess the current atmospheric methane budget and its future trends, it is essential to apportion and quantify the anthropogenic methane emissions to specific sources. This poses a significant challenge in the under‐sampled Middle East, where estimates predominantly depend on remote sensing observations and bottom‐up reporting of national emissions. Here, we present in situ shipborne observations of greenhouse gases (GHGs) and non‐methane hydrocarbons (NMHCs) collected along a >10,000‐km route from Vigo, Spain, to Abu Dhabi, UAE. By comparing our observations with Lagrangian dispersion model simulations, coupled with two methane emission inventories, we identify periods of considerable mismatch and apportion the responsible sources. Employing interspecies relationships with NMHCs has enabled the characterization of methane emissions from oil and gas (O&G) operations, urban centers, Red Sea deep water, enteric fermentation, and agriculture across diverse atmospheric environments. Our analysis reveals that the Suez area is a regional emission hotspot, where simulations consistently underestimate the methane emission sources. Importantly, the Middle Eastern O&G sector has been identified as an additional source of considerable uncertainty. Here, methane emissions were alternately underestimated and overestimated by the two inventories, exposing significant gaps in our understanding of fuel exploitation‐related emissions in the Middle East. This underscores the need for further targeted field campaigns and long‐term observations to improve the accuracy of emission data in the inventories.

A modern concept of Lagrangian hydrodynamics

AbstractWe offer a modern interpretation of Lagrangian hydrodynamics as employed in Lagrangian simulations of compressible fluid flow. Our main result is to show that artificial viscosity, traditionally viewed as a numerical artifice to control unphysical oscillations in flows with shocks, actually represents a physical process and is necessary to derive accurate simulations in any compressible flow. We begin by reviewing the origins of two numerical devices, artificial viscosity and finite‐volume methods. We proceed to construct a mathematical (PDE) model that incorporates those numerics and in which a new length scale, the observer, arises representing the discretization. Associated with that length scale, there are new inviscid fluxes that are the artificial viscosity as first formulated by Richtmyer and an artificial heat flux postulated by Noh but typically not included in Lagrangian codes. We discuss the connection of our results to bivelocity hydrodynamics. We conclude with some speculation as to the direction of future developments in multidimensional Lagrangian codes as computers get faster and have larger memories.

From source to sink: part 1-characterization and Lagrangian tracking of riverine microplastics in the Mediterranean Basin.

The Mediterranean Sea is one of the most critically polluted areas due to its semi-enclosed structure and its highly anthropized shoreline. Rivers are significant vectors for pollutant transfers from the continental to the marine environment. In this context, a 3D Lagrangian simulation of the dispersion of riverine microplastics (MPs) was performed, which included the application of a recently developed model that reassessed the MP fluxes discharged by rivers. MP physical properties from river samples were further investigated to approximate vertical displacement in modeled ocean currents. The use of a high-resolution circulation model, integrating Stokes drift, turbulent diffusion, and MP sinking and rising velocities, enabled us to establish stock balances. Our simulation suggested that 65% of river inputs may be made of floating MPs drifting in the surface layer and 35% of dense MPs sinking to deeper layers. The Eastern Mediterranean tends to accumulate floating MPs, primarily originating from the Western Mediterranean Basin, where major river sources are concentrated. After 2 years of simulation, modeled stranding sequestered 90% of the MP inputs, indicating relatively short average residence times from a few days to months at most for particles at sea. Although spatial distribution patterns stabilized after this period and a steady state may have been approached, the surface concentrations we modeled generally remained below field observations. This suggested either an underestimation of sources (rivers and unaccounted sources), by a factor of 6 at most, or an overestimation of MP withdrawal through stranding, to be reduced from 90 to around 60% or less if unaccounted sinks were considered.

An Improved Comprehensive Atomization Model for Pressure Swirl Atomizers

This study presents an improved comprehensive atomization model for a pressure swirl atomizer. The model integrates internal flow predictions, linear instability analysis of a swirling annular liquid sheet, primary atomization sub-model, and droplet velocity sub-model. Measurement data combined with the inviscid theory model predict the internal flow, providing liquid sheet velocity and thickness at the atomizer outlet. The dispersion relation of surface disturbances is obtained through linear instability analysis. A primary breakup predictive model for particle size distribution is constructed based on the wavelength and growth rate within the full unstable wavenumber range of the dispersion relation. Assuming uniform circumferential distribution and a normal distribution of spray angles, the droplet velocity is assigned according to the liquid sheet velocity. The model is implemented into Eulerian–Lagrangian simulations as initial conditions for discrete phase droplets to simulate the spray field. Results show the model can accurately predict the Sauter mean diameter with an error of less than 6% and effectively predicts the spray structure and spray cone angle. The dependency of the model on its parameters is also studied, determining that the values of the ligament constant and dispersion angle have an obvious impact on the prediction of Sauter mean diameter and spray structure.

Lagrangian Versus Eulerian Spectral Estimates of Surface Kinetic Energy Over the Global Ocean

AbstractIn this study, we conducted a novel massive Lagrangian simulation experiment based on a global 1/48° tide‐resolving numerical simulation of the ocean circulation. This first‐time twin experiment enables a comparison between Eulerian (fixed‐point) and Lagrangian (along‐flow) estimates of kinetic energy (KE) across the global ocean, and the quantification of systematic differences between both types of estimations. This comparison represents an important step forward for the mapping of upper ocean high‐frequency variability from Lagrangian observations of the Global Drifter Program. Eulerian KE rotary frequency spectra and band‐integrated energy levels (e.g., tidal and near‐inertial) serve as references and are compared to Lagrangian estimates. Our analysis reveals that, except for the near‐inertial band, Lagrangian velocity spectra are systematically smoother, for example, with wider and lower spectral peaks compared to Eulerian counterparts. On average, Lagrangian KE levels derived from spectral band integrations tend to underestimate Eulerian KE levels at low‐frequency and tidal bands, especially in regions with strong low‐frequency KE. Better agreement between Lagrangian and Eulerian low‐frequency and tidal KE levels is generally found in regions with weak low‐frequency KE and/or convergent surface circulation, where Lagrangian particles tend to accumulate. Conversely, Lagrangian and Eulerian near‐inertial spectra and energy levels are comparable. Our results demonstrate that Lagrangian estimates may provide a distorted view of low‐frequency and tidal variance. To accurately map near‐surface velocity climatology at these frequencies from drifter database, conversion methods accounting for the Lagrangian bias need to be developed.

Anomalous ocean currents and European anchovy dispersal in the Iberian ecosystem

Unlike other upwelling areas where sardine and anchovy species dominate the pelagic ecosystems, the Western Iberian ecosystem has been consistently dominated by European sardine Engraulis encrasicolus, while anchovy had a residual presence from the start of acoustic surveys, in 1989, to 2014. Since 2015, the abundance of anchovy in the Western Iberian margins has sharply increased and continues to show an increasing trend as of 2023. It is unclear if this increase is a result of dispersal from nearby recruitment areas, higher survival rates of early life stages due to favorable environmental conditions, or both. We used a set of different models to simulate the dispersion and survival of anchovy early life stages in the Iberian region for the years preceding the increase in anchovy abundance. An ocean model simulation with the model CROCO provided the fields used as background for Lagrangian simulations coupled to an individual-based model of anchovy eggs and larvae. We simulated the years 2013-2015, and the results show that in 2014 and 2015, anomalous upper-ocean circulation patterns with strong and persistent westward currents transported a large number of eggs and larvae from the Bay of Biscay (BoB) westward along the Northern Iberian margin. The maximum transport occurred in June and July 2015, when 8 and 4%, respectively, of the eggs spawned in the BoB potentially reached the Iberian west coast as larvae. This process might explain the increase in anchovy abundance in the Western Iberian ecosystem. The results of the study show that episodes of anomalous intense ocean currents, when coincident with high presence of eggs, can lead to the colonization of new areas, and connectivity between areas varies dramatically with time.

Dispersal and connectivity modelling simulations for invertebrate larvae passing through the Strait of Gibraltar

Abstract The link between the northeastern Atlantic and Mediterranean Sea created by the Strait of Gibraltar and the adjacent Iberian and Moroccan coasts marks remarkable transition areas between distinct environments that harbour a diverse mixture of species. The area is interesting regarding marine connectivity and the transport of pelagic invertebrate larvae, crucial knowledge to manage over-exploited populations, and minimize the impacts of climate change and anthropogenic activities. Biophysical models were developed, combining oceanic and particle-tracking Lagrangian simulations with in situ zooplankton distribution data. The conditions driving the larval exchange between the sub-basins and the connectivity throughout the region were explored, using crustacean decapod larvae as biological references. The potential exchange between both sub-basins was confirmed, although specific larval traits revealed contrasting scenarios. The simulations showed that slope-dwelling and mesopelagic larvae have advantage when crossing from the Alboran into the Atlantic, in comparison with shelf-dwelling and epipelagic larvae. Transport pathways and retention areas were identified, and passive drifts were shown to increase the dispersal range of the simulations. The spatial origin of the larval release, larval duration, vertical distribution, and the interaction of larvae with the oceanic features are presented as the main factors impacting the effective larval input into the Atlantic or Mediterranean basins.

Zweifach-Fung Microfluidic Device for Efficient Microparticle Separation: Cost-Effective Fabrication Using CO2 Laser-Ablated PMMA.

Microfluidic separators play a pivotal role in the biomedical and chemical industries by enabling precise fluid manipulations. Traditional fabrication of these devices typically requires costly cleanroom facilities, which limits their broader application. This study introduces a novel microfluidic device that leverages the passive Zweifach-Fung principle to overcome these financial barriers. Through Lagrangian computational simulations, we optimized an eleven-channel Zweifach-Fung configuration that achieved a perfect 100% recall rate for particles following a specified normal distribution. Experimental evaluations determined 2 mL/h as the optimal total flow rate (TFR), under which the device showcased exceptional performance enhancements in precision and recall for micrometer-sized particles, achieving an overall accuracy of 94% ± 3%. Fabricated using a cost-effective, non-cleanroom method, this approach represents a significant shift from conventional practices, dramatically reducing production costs while maintaining high operational efficacy. The cost of each chip is less than USD 0.90 cents and the manufacturing process takes only 15 min. The development of this device not only makes microfluidic technology more accessible but also sets a new standard for future advancements in the field.

Human-induced warming accelerates local evapotranspiration and precipitation recycling over the Tibetan Plateau

The Tibetan Plateau faces changing precipitation and environmental conditions affecting alpine ecosystems and downstream freshwater sustainability. While aerosol influence has been highlighted, how human-induced greenhouse warming impacts the plateau’s moisture recycling remains unclear. Here we show that the Tibetan Plateau’s recent precipitation changes result from enhanced precipitation recycling and moisture convergence that offset the decline in monsoon- and westerly-associated moisture transport based on 40-year Lagrangian simulations and water budget analyses. Local evapotranspiration is observed to increase faster in percentage than precipitation, a trend expected to continue in future warming scenarios according to climate projections. Greenhouse gas emission causes widespread wetting while weakening the southerly monsoons across the Himalayas, heightening the sensitivity of precipitation to evapotranspiration and thereby local land surface changes. This trend exacerbates vulnerability in the water cycle of high mountain Asia, calling for proactive management to address potential risks and ensure future water and food security in Asia.

Pragmatic Prediction Model of Droplet Trajectory in a Turbine Cascade

Abstract Droplet deposition on a turbine cascade is important for the turbine system performance but its experimental analysis is difficult. Thus, the simulation of a droplet liquid phase in a gas flow field was studied to optimize turbine cascade design. However, the computational fluid dynamics (CFD)-based approach for such droplet problems requires enormous costs. Thus, the application of CFD simulation in the turbine blade's early-stage design is challenging, requiring iterative optimization for adjusting design with performance prediction. Therefore, this study proposed an analytical prediction method, having a reasonable cost and moderate accuracy, as an alternative to the whole multi-phase numerical simulation approach. The proposed method predicts droplet motion using the outline of the turbine blade and gas–liquid physical properties. Furthermore, the approach was validated by performing a three-dimensional Eulerian–Lagrangian simulation with low-pressure turbine blade T106. It was found that the droplet trajectories in the turbine cascade are governed by Stokes number. Furthermore, the streamlines of the gas flow were characterized by the shape of the turbine blade. The proposed model reproduced droplet trajectories obtained using CFD within an error margin of 10%. Consequently, it was concluded that the proposed analytical model is a promising approach to predict the droplet trajectory in a turbine cascade, obtained by the three-dimensional numerical simulation at a low cost.

Does the Asian summer monsoon play a role in the stratospheric aerosol budget of the Arctic?

Abstract. The Asian summer monsoon has a strong convectional component with which aerosols are able to be lifted up into the lower stratosphere. Due to usually long lifetimes and long-range transport aerosols remain there much longer than in the troposphere and are also able to be advected around the globe. Our aim of this study is a synergy between simulations by Chemical Lagrangian Model of the Stratosphere (CLaMS) and KARL (Koldewey Aerosol Raman Lidar) at AWIPEV, Ny-Ålesund in the Arctic, by comparing CLaMS results with exemplary days of lidar measurements as well as analyzing the stratospheric aerosol background. We use global three-dimensional Lagrangian transport simulations including surface origin tracers as well as back trajectories to identify source regions of the aerosol particles measured over Ny-Ålesund. We analyzed lidar data for the year 2021 and found the stratosphere generally clear, without obvious aerosol layers from volcanic eruptions or biomass burnings. Still an obvious annual cycle of the backscatter coefficient with higher values in late summer to autumn and lower values in late winter has been found. Results from CLaMS model simulations indicate that from late summer to early autumn filaments with high fractions of air which originate in South Asia – one of the most polluted regions in the world – reach the Arctic at altitudes between 360 and 380 K potential temperature. We found a coinciding measurement between the overpass of such a filament and lidar observations, and we estimated that backscatter and depolarization increased by roughly 15 % during this event compared to the background aerosol concentration. Hence we demonstrate that the Asian summer monsoon is a weak but measurable source for Arctic stratospheric aerosol in late summer to early autumn.

Deep inflow transport and dispersion in the Gulf of St. Lawrence revealed by a tracer release experiment

The Gulf of St. Lawrence is increasingly affected by bottom water hypoxia; however, the timescales and pathways of deep water transport remain unclear. Here, we present results from the Deep Tracer Release eXperiment (TReX Deep), during which an inert SF5CF3 tracer was released inshore of Cabot Strait at 279 m depth to investigate deep inflow transport and mixing rates. Dispersion was also assessed via neutrally-buoyant Swish floats. Our findings indicate that the tracer moves inland at 0.5 cm s−1, with an effective lateral diffusivity of 2 × 102 m2 s−1 over 1 year. Simplified 1D simulations suggest inflow water should reach the estuary head in 1.7 years, with the bulk arriving after 4.7 years. Basin-wide effective vertical diffusivity is around 10−5 m2 s−1 over 1 year; however, vertical diffusivity increases near the basin slopes, suggesting that turbulent boundary processes influence mixing. These results are compared to Lagrangian simulations in a regional 3D model to evaluate the capacity to model dispersion in the Gulf.

UAV path planning algorithm based on Deep Q-Learning to search for a floating lost target in the ocean

In the context of real world application, Search and Rescue Missions on the ocean surface remain a complex task due to the large-scale area and the forces of the ocean currents, spreading lost targets and debris in an unpredictable way. In this work, we present a Path Planning Approach to search for a lost target on ocean surface using a swarm of UAVs. The combination of GlobCurrent dataset and a Lagrangian simulator is used to determine where the particles are moved by the ocean currents forces while Deep Q-learning algorithm is applied to learn from their dynamics. The evaluation results of the trained models show that our search strategy is effective and efficient. Over a total search area (red Sea zone), surface of 453422 Km2, we have shown that our strategy Search Success Rate is 98.61%, the maximum Search Time to detection is 15 days and the average Search Time to detection is almost 15 h.

Spatial distribution of small microplastics in the Norwegian Coastal Current

High concentrations of microplastic (MP) particles have been reported in the Arctic Ocean. However, studies on the high-resolution lateral and vertical transport of MPs from the European waters to the Arctic are still scarce. Here, we provide information about the concentrations and compositions of MPs in surface, subsurface, and deeper waters (< 1 m, ∼ 4 m, and 17–1679 m) collected at 18 stations on six transects along the Norwegian Coastal Current (NCC) using an improved Neuston Catamaran, the COntinuos MicroPlastic Automatic Sampling System (COMPASS), and in situ pumps, respectively. FTIR microscopy and spectroscopy were applied to measure MP concentration, polymer composition, and size distribution. Results indicate that the concentrations of small microplastics (SMPs, <300 μm) varied considerably (0–1240 MP m−3) within the water column, with significantly higher concentrations in the surface (189 MP m−3) and subsurface (38 MP m−3) waters compared to deeper waters (16 MP m−3). Furthermore, the average concentration of SMPs in surface water samples was four orders of magnitude higher than the abundance of large microplastics (LMPs, >300 μm), and overall, SMPs <50 μm account for >80 % of all detected MPs. However, no statistically significant geographical patterns were observed in SMP concentrations in surface/subsurface seawaters between the six sampling transects, suggesting a relatively homogeneous horizontal distribution of SMPs in the upper ocean within the NCC/Norwegian Atlantic Current (NwAC) interface. The Lagrangian particle dispersal simulation model further enabled us to assess the large-scale transport of MPs from the Northern European waters to the Arctic.

Optimization of Dropwise Condensation of Steam over Hybrid Hydrophobic–Hydrophilic Surfaces via Enhanced Statistically Based Heat Transfer Modelization

Steam condensation over a hybrid hydrophobic–hydrophilic surface is modeled via simplified heat transfer modelization. Filmwise condensation is assumed over the hydrophilic region. The standard film model is improved, accounting for the liquid flow rate crossing the hydrophobic–hydrophilic boundaries. A threshold for flooding occurrence is also presented. Dropwise condensation is assumed over the hydrophobic region. Compared to the heat transfer models in the literature, based on the statistical drop size distribution, a novel correlation is used for the size distribution of small droplets. The correlations of both the liquid flow rate crossing the hydrophobic–hydrophilic boundary and the size distribution of small drops are derived via Lagrangian simulations, using an in-house code previously developed and validated by the authors. The heat transfer model is validated with experimental data in the literature involving a hybrid surface, composed by alternate vertical hydrophobic–hydrophilic stripes. Then, the optimization of the hybrid surface geometry is performed in terms of hydrophobic width and hydrophilic width, with the aim of enhancing the heat flux.

Accelerating Lagrangian transport simulations on graphics processing units: performance optimizations of Massive-Parallel Trajectory Calculations (MPTRAC) v2.6

Abstract. Lagrangian particle dispersion models are indispensable tools for the study of atmospheric transport processes. However, Lagrangian transport simulations can become numerically expensive when large numbers of air parcels are involved. To accelerate these simulations, we made considerable efforts to port the Massive-Parallel Trajectory Calculations (MPTRAC) model to graphics processing units (GPUs). Here we discuss performance optimizations of the major bottleneck of the GPU code of MPTRAC, the advection kernel. Timeline, roofline, and memory analyses of the baseline GPU code revealed that the application is memory-bound, and performance suffers from near-random memory access patterns. By changing the data structure of the horizontal wind and vertical velocity fields of the global meteorological data driving the simulations from structure of arrays (SoAs) to array of structures (AoSs) and by introducing a sorting method for better memory alignment of the particle data, performance was greatly improved. We evaluated the performance on NVIDIA A100 GPUs of the Jülich Wizard for European Leadership Science (JUWELS) Booster module at the Jülich Supercomputing Center, Germany. For our largest test case, transport simulations with 108 particles driven by the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 reanalysis, we found that the runtime for the full set of physics computations was reduced by 75 %, including a reduction of 85 % for the advection kernel. In addition to demonstrating the benefits of code optimization for GPUs, we show that the runtime of central processing unit (CPU-)only simulations is also improved. For our largest test case, we found a runtime reduction of 34 % for the physics computations, including a reduction of 65 % for the advection kernel. The code optimizations discussed here bring the MPTRAC model closer to applications on upcoming exascale high-performance computing systems and will also be of interest for optimizing the performance of other models using particle methods.

On the efficacy of facial masks to suppress the spreading of pathogen-carrying saliva particles during human respiratory events: Insights gained via high-fidelity numerical modeling.

Respiratory fluid dynamics is integral to comprehending the transmission of infectious diseases and the effectiveness of interventions such as face masks and social distancing. In this research, we present our recent studies that investigate respiratory particle transport via high-fidelity large eddy simulation coupled with the Lagrangian particle tracking method. Based on our numerical simulation results for human respiratory events with and without face masks, we demonstrate that facial masks could significantly suppress particle spreading. The studied respiratory events include coughing and normal breathing through mouth and nose. Using the Lagrangian particle tracking simulation results, we elucidated the transport pathways of saliva particles during inhalation and exhalation of breathing cycles, contributing to our understanding of respiratory physiology and potential disease transmission routes. Our findings underscore the importance of respiratory fluid dynamics research in informing public health strategies to reduce the spread of respiratory infections. Combining advanced mathematical modeling techniques with experimental data will help future research on airborne disease transmission dynamics and the effectiveness of preventive measures such as face masks.