Number Concentration Of Nanoparticles Research Articles

Numerical study of fluid flow and heat transfer for flow of Cu-Al2O3-water hybrid nanofluid in a microchannel heat sink

The use of micro-electronic devices in many applications such as aerospace, telecommunications, micro-electronics, robotics is drastically increasing and they need efficient cooling system. Micro-channel heat sinks (MCHS) are getting significant importance due to their very high surface to volume ratio and high heat dissipation rate. The hybrid nanofluids playing a vital role as cooling fluids in various thermal transportation applications due to their extraordinary heat transport characteristics. A numerical study is taken up for laminar flow of hybrid nanofluid as a heat transport medium in a rectangular MCHS to realize thermal and hydrodynamic behaviour in forced convection. The influence of Reynolds number (Re) and volume concentration of nanoparticles in Cu-Al2O3/water hybrid nanofluid on MCHS performance is investigated in the present paper. The correlations presented in the literature are used to calculate the properties of hybrid nanofluids. For various mixture ratios of 25–75%, 50–50% and 75–25% hybrid nanofluids the heat transport rate and pressure drop are calculated at different Reynolds numbers and compared with mono nanofluids of Cu-water (H2O) and Al2O3-water. An enhancement in heat transfer rate is observed with raise in volume fraction and marginal increase in pressure drop is observed for hybrid nanofluids over mono nanofluids of Cu-water and Al2O3-water. The results indicate an increase of 13.2% and 23.07% in Nusselt number for Cu-Al2O3/water hybrid nanofluid compared with Cu/water and Al2O3/water mono nanofluids respectively at 2.5% volume fraction. It is found from the numerical results that the pumping power requirement is less for hybrid Cu-Al2O3/water nanofluid compared to Cu/water nanofluids and an increase of 430 Pa compared to pure water. The data existing for Al2O3-water nanofluid in the literature is used to validate the present model.

Characterization of the Silver Species Released From Clothing by Single Particle–Inductively Coupled Plasma–Mass Spectrometry Using a Microsecond Dwell Time

In this study the silver species were identified that leached into artificial sweat from commercially available clothing products that were in direct contact with skin. Single particle-inductively coupled plasma mass-spectrometry (SP-ICP-MS) is capable of simultaneously determining silver nanoparticles (AgNPs) and dissolved silver (Ag+), especially when dwell time is used in microsecond range. The effect of Ag+ concentration for the determination of 40 and 70 nm AgNPs was investigated and AgNPs were characterized accurately up to 2 ng mL−1 and 15 ng mL−1 Ag+, respectively. Under the optimized conditions, the limit of detection for nanoparticle number concentration (LODconc) and the limit of detection for nanoparticle size (LODsize) of the proposed SP-ICP-MS method were 5.5 × 102 particle mL−1 and 17 nm, respectively. According to the results, silver was present in artificial sweat solution in the dissolved form, which was confirmed by a spectrofluorometric assay and ultracentrifugation. In addition, the released quantity of silver from underwear was higher than from socks, which may be related to the differences in the textiles and their manufacturing processes.

Application of Single-Particle ICP-MS to Determine the Mass Distribution and Number Concentrations of Environmental Nanoparticles and Colloids

Analyzing the elemental compositions and size distributions of nanoparticles, colloids, and their aggregates in environmental samples represents a key task in understanding contaminant, substrate, and nutrient cycling. Single-particle ICP-MS (spICP-MS) is a high-throughput method that is capable of providing the elemental mass of thousands of particles within minutes. The challenge, however, lies in data analysis and interpretation, especially for complex environmental samples. Here we present successful applications of spICP-MS for environmental samples. We first analyzed the homoaggregation behavior of synthetic microplastic and magnetite (abiogenic and biogenic) nanoparticles. The measured distribution of aggregate mass was described as a function of the number of primary particles/aggregate (Npp). In tandem with dynamic light scattering data, differences in aggregates’ compactness (primary particles per nanometer) between samples can be determined. Second, we showed how sequential elemental analysis allows evaluation of the mobility of a toxic arsenic metalloid and its inferred association with colloidal Fe(III) (oxyhydr)oxides. Finally, we investigated the composition of heterogeneous iron–carbon-rich colloidal flocs, highlighting distinct colloidal Fe and C distributions and C/Fe ratios between samples from different permafrost thawing stages. On the basis of our results, we provide guidelines for successful sample preparation and promising future spICP-MS opportunities and applications with environmental samples.

Quantification of Nanoparticles in Dispersions Using Transmission Electron Microscopy.

The quantification of the particle size and the number concentration (PNC) of nanoparticles (NPs) is key for the characterization of nanomaterials. Transmission electron microscopy (TEM) is often considered as the gold standard for assessing the size of NPs; however, the TEM sample preparation suitable for estimating the PNC based on deposited NPs is challenging. Here, we use an ultrasonic nebulizer (USN) to transfer NPs from aqueous suspensions into dried aerosols which are deposited on TEM grids in an electrostatic precipitator of an aerosol monitor. The deposition efficiency of the electrostatic precipitator was ≈2%, and the transport efficiency of the USN was ≈7%. Experiments using SiO2 NPs (50–200 nm) confirmed an even deposition of the nebulized particles in the center of the TEM grids. PNCs of the SiO2 NPs derived from TEM images underestimated the expected PNCs of the suspensions by a factor of up to three, most likely resulting from droplet coagulation and NP aggregation in the USN. Nevertheless, single particles still dominated the PNC. Our approach results in reproducible and even deposition of particles on TEM grids suitable for morphological analysis and allows an estimation of the PNC in the suspensions based on the number of particles detected by TEM.

Enhancement of nanoparticle formation and growth during the COVID-19 lockdown period in urban Beijing

Abstract. Influenced by the spread of the global 2019 novel coronavirus (COVID-19) pandemic, primary emissions of particles and precursors associated with anthropogenic activities decreased significantly in China during the Chinese New Year of 2020 and the lockdown period (24 January–16 February 2020). The 2-month measurements of the number size distribution of neutral particles and charged ions showed that during the lockdown (LCD) period, the number concentration of particles smaller than 100 nm decreased by approximately 40 % compared to the pre-LCD period in January. However, the accumulation mode particles increased by approximately 20 % as several polluted episodes contributed to secondary aerosol formation. In this study, new particle formation (NPF) events were found to be enhanced in the nucleation and growth processes during the LCD period, as indicated by the higher formation rate of 2 nm particles (J2) and the subsequent growth rate (GR). The relevant precursors, e.g., SO2 and NO2, showed a clear reduction, and O3 increased by 80 % during LCD period, as compared with pre-LCD. The volatile organic vapors showed different trends due to their sources. The proxy sulfuric acid during the LCD period increased by approximately 26 %, as compared with pre-LCD. The major oxidants (O3, OH, and NO3) of VOCs were also found to be elevated during LCD. That indicated higher J2 and GR (especially below 5 nm) during the LCD period were favored by the increased concentration level of condensing vapors and decreased condensation sink. Several heavy haze episodes have been reported by other studies during the LCD period; however, the increase in nanoparticle number concentration should also be considered. Some typical NPF events produced a high number concentration of nanoparticles that intensified in the following days to create severe aerosol pollution under unfavorable meteorological conditions. Our study confirms a significant enhancement of the nucleation and growth process of nanoparticles during the COVID-19 LCD in Beijing and highlights the necessity of controlling nanoparticles in current and future air quality management.

Occupational exposure risk during spraying of biocidal paint containing silver nanoparticles

The study assessed potential to exceed occupational exposure limits while spraying paint with and without a silver nanoparticle biocidal additive. A tradesperson performed the tasks in a sealed chamber with filtered air supply. Integrated air sampling entailed transmission electron microscopy with energy dispersive X-ray analysis, direct-reading of particle number concentrations, and determination of silver mass concentration by NIOSH Method 7300. Silver nanoparticles were primarily embedded in paint spray droplets but also observed as isolated particles. Using an α-level of 0.05, median nanoparticle number concentrations did not differ significantly when spraying conventional vs. biocidal paint, although statistically significant differences were observed at specific particle size ranges <100 nm. The geometric mean concentration of total silver while spraying biocidal paint (n = 6) was 2.1 µg/m3 (95% CI: 1.5–2.8 µg/m3), and no respirable silver was detected (<0.50 µg/m3). The results address a lack of silver nanoparticle exposure data in construction and demonstrate the feasibility of a practical sampling approach. Given similar conditions, the measurements suggest a low probability of exceeding a proposed silver nanoparticle exposure limit of 0.9 µg/m3 as an airborne 8-hr time-weighted average respirable mass concentration. A full workday of exposure to respirable silver at the highest possible level in this study (<0.50 µg/m3) would not exceed the exposure limit, although limitations in comparing short task-based exposures to an 8-hr exposure limit must be noted. There was airflow in the study chamber, whereas exposure levels could increase over time in work environments lacking adequate ventilation. Potential to exceed the exposure limit hinged upon the respirable fraction of the paint mist, which could vary by material and application method. Additional research would improve understanding of silver nanoparticle exposure risks among construction trades, and biological responses to these exposures. Given the potential for exposure variability on construction jobsites, safety and health professionals should be cognizant of methods to assess and control silver nanoparticle exposures.

Occupational exposure to nanoparticles originating from welding - case studies from the Czech Republic.

Nanomaterials are virtually ubiquitous as they are created by both natural processes and human activities. The amount of occupational exposure to unintentionally released nanoparticles can, therefore, be substantial. The aim of the study was to determine the concentrations of incidental nanoparticles that workers can be exposed to during welding operations and to assess related health risks. The specific focus on welding operations was determined based on the fact that other case studies on the manufacturing industry confirm significant exposure to incidental nanoparticles during welding. In the Czech Republic, 92% of all industrial workers are employed in the manufacturing industry, where welding operations are amply represented. The particle number concentrations of particles in the size range of 20-1000 nm and particle mass concentrations of inhalable and PM1 fractions were determined via measurements carried out at 15-minute intervals for each welding operation by static sampling in close proximity to the worker. Measurements were obtained using the following instruments: NanoScan SMPS 3910, Optical Particle Sizer OPS 3330, P-TRAK 8525 and DustTrak DRX 8534. The assessed operations were manual arc welding and automatic welding. The observed average particle number concentrations for electric arc welders ranged 84×103-176×103 #/cm3, for welding machine operators 96×103-147×103 #/cm3, and for a welding locksmith the obtained average concentration was 179×103 #/cm3. The determined average mass concentration of PM1 particles ranged 0.45-1.4 mg/m3. Based on the conducted measurements, it was confirmed that there is a significant number of incidental nanoparticles released during welding operations in the manufacturing industry as a part of production and processing of metal products. The recommended occupational exposure limits for nanoparticle number concentrations were exceeded approximately 4-8 times for all assessed welding operations. The use of local exhaust ventilation in conjunction with personal protective equipment, including FFP2 or FFP3 particle filters, for welding is, therefore, recommended. Med Pr. 2021;72(3):219-30.

Detection, size characterization and quantification of silver nanoparticles in consumer products by particle collision coulometry.

Silver nanoparticles (AgNPs) are widely used in industrial and consumer products owing to its antimicrobial nature and multiple applications. Consequently, their release into the environment is becoming a big concern because of their negative impacts on living organisms. In this work, AgNPs were detected at a potential of + 0.70V vs. Ag/AgCl reference electrode, characterized, and quantified in consumer products by particle collision coulometry (PCC). The electrochemical results were compared with those measured with electron microscopy and single-particle inductively coupled plasma mass spectrometry. The theoretical and practical peculiarities of the application of PCC technique in the characterization of AgNPs were studied. Reproducible size distributions of the AgNPs were measured in a range 10-100nm diameters. A power allometric function model was found between the frequency of the AgNPs collisions onto the electrode surface and the number concentration of nanoparticles up to a silver concentration of 1010L-1 (ca. 25ngL-1 for 10nm AgNPs). A linear relationship between the number of collisions and the number concentration of silver nanoparticles was observed up to 5 × 107L-1. The PCC method was applied to the quantification and size determination of the AgNPs in three-silver containing consumer products (a natural antibiotic and two food supplements). The mean of the size distributions (of the order 10-20nm diameters) agrees with those measured by electron microscopy. The areas of current spikes from the chronoamperogram allow the rapid calculation of size distributions of AgNPs that impact onto the working electrode.

An insight into the determination of size and number concentration of silver nanoparticles in blood using single particle ICP-MS (spICP-MS): feasibility of application to samples relevant to in vivo toxicology studies

Systematic method development for the determination of number concentration and size of silver nanoparticles in blood for the purpose of application to the typical workflow of an in vivo toxicology study.

Characterization of nanoparticles using coupled gel immobilization and label-free optical imaging.

Accurate quantification of number concentration of nanoparticles (NPs) is critical for their biomedical and catalytic applications. We developed a novel NP analysis platform based on coupled gel immobilization and a three-dimensional (3D) scattered light imaging (SLI) platform. This imaging-based technique enables high-throughput analysis of silver nanoparticles (AgNPs) at single-particle level without the need for particle labeling or modification. This is a well-established quantitative characterization technique that can simultaneously measure the number concentration and size distribution of AgNPs. It also demonstrates the visualization and quantification of the size and 3D morphology of AgNP agglomerates in solution.

CFD Study Based on Effect of Employing the Single-Walled Carbon Nanotube (SWCNT) and Graphene Quantum Dots (GQD) Nanoparticles and a Particular Fin Configuration on the Thermal Performance in the Shell and Tube Heat Exchanger

In this research, the thermal attributes of shell and finned tube heat exchanger such as thermal efficiency, pressure drop, heat transfer rate and average temperature in the tube side of heat exchanger with using the different volume concentration of nanoparticles (SWCNT and Graphene quantum dot) at the various Reynolds number by applying either fin blades and without fin blades have been conducted numerically. In this heat exchanger the hot fluid or nanofluid flows in the tube section and cold fluid or pure water moves in the shell side. As regarding to results obtained the majority of thermal characteristics like heat transfer rate, pressure drop and effectiveness enhanced with augmentation of Reynolds number and increasing of volume concentration of nanofluids to 1% volumetric of working fluid whereas at the higher volume concentrations of nanoparticles (upper from 1% volumetric) the thermal properties of heat exchanger decreased generally. Also pressure drop intensifies with increment of Reynolds number and volume concentration of nanoparticles that at higher Reynolds number the effects of nanoparticles on the pressure drop were more noticeable. The average temperature of heat exchanger in the end section of inside tubes increased with augmentation of Reynolds number and nanoparticles. Finally, according to the results obtained in this study, most impression on the thermal attributes enhancement was found by employing of finned tubes compared to other factor which this factor increased heat transfer rate of heat exchanger by almost 188% also the effects of nanoparticles at the high levels of volume concentration especially for 5% of SWCNT nanoparticle on the pressure drop obtained about 80% compared to the base fluid.

Monitoring AuNP Dynamics in the Blood of a Single Mouse Using Single Particle Inductively Coupled Plasma Mass Spectrometry with an Ultralow-Volume High-Efficiency Introduction System.

Gold nanoparticles (AuNPs) are increasingly being used as diagnostic and therapeutic agents owing to their excellent properties; however, there is not much data available on their dynamics in vivo on a single particle basis in a single mouse. Here, we developed a method for the direct analysis of nanoparticles in trace blood samples based on single particle inductively coupled plasma-mass spectrometry (spICP-MS). A flexible, highly configurable, and precisely controlled sample introduction system was designed by assembling an ultralow-volume autosampler (flow rate in the range of 5-5000 μL/min) and a customized cyclonic spray chamber (transfer efficiency up to 99%). Upon systematic optimization, the detection limit of the nanoparticle size (LODsize) of AuNPs in ultrapure water was 19 nm, and the detection limit of the nanoparticle number concentration (LODNP) was 8 × 104 particle/L. Using a retro-orbital blood sampling method and subsequent dilution, the system was successfully applied to track the dynamic changes in size and concentration for AuNPs in the blood of a single mouse, and the recovery for the blood sample was 111.74%. Furthermore, the concentration of AuNPs in mouse blood reached a peak in a short period of time and, then, gradually decreased. This study provides a promising technique for analyzing and monitoring the size and concentration of nanoparticles in ultralow-volume blood samples with low concentrations, making it a powerful tool for analyzing and understanding the fate of nanoparticles in vivo.

Comparative Study of Thermal and Hydraulic Performance of Three-Fluid Tubular Heat Exchanger With CuO–Water Nanofluid: Single-Phase and Multi-Phase Approaches

Abstract Comparative analysis of the thermal and hydraulic performance of three-fluid tubular heat exchanger has been carried out numerically. Single-phase and multi-phase approaches for the turbulent flow of CuO–water nanofluids have been applied. The effect of Reynolds number (2500–10,000) and volume concentration of nanoparticles (0–3%) on the overall performance of the selected heat exchanger has been investigated. The numerical simulation has been performed using a finite volume approach in commercial computational fluid dynamics (CFD) software for two flow arrangements (parallel and counter). Nusselt number was found to increase with the growth in Reynolds number as well as volume concentration of nanoparticles in both the flow arrangements. Particularly, for a maximum volume concentration of nanoparticles (φ = 3%), single-phase approach resulted in an increase of 8.94% for parallel and 11.52% for counterflow arrangements. However, multi-phase approach produced a remarkable increase of 30.37% for parallel and 32.04% for counterflow arrangement. Single-phase approach was applied for treating the nanofluids as homogenous fluids with effective thermophysical properties, meaning that the entire suspension is assumed to act as a single unit with the same velocity. However, the multi-phase model was applied to separately treat the two phases with different velocities.

In Situ Quantitative Observation of Hygroscopic Growth of Single Nanoparticle Aerosol by Surface Plasmon Resonance Microscopy.

Aerosol particle hygroscopicity is an important factor in visibility reduction, cloud formation, radiation forcing, and the global climate. The high number concentration of nanoparticles (defined as particles with diameters below 100 nm) means that their hygroscopic growth abilities and potential contributions to the climate and environment are significant. Therefore, a rapid and accurate in situ analysis method for single nanoparticle hygroscopic growth in an atmospheric environment is important to characterize the effects of the particle's physical and chemical properties in this process. In this work, surface plasmon resonance microscopy with azimuthal rotation illumination (SPRM-ARI) is used to observe the hygroscopic growth and water content of single nanoparticles in situ. The hygroscopic growth results of a single-component nanoparticle are well matched with the extended aerosol inorganic model (E-AIM) results, and the proposed method remains reliable even when the relative humidity (RH) exceeds 90%. For a bicomponent nanoparticle (with NaCl as the primary content), the presence of a component without deliquescence phase transitions under increasing humidity conditions causes the measured data to differ from both the Zdanovskii-Stokes-Robinson (ZSR) model and E-AIM predictions in the low RH range. However, because of their complete liquefaction, the growth factor (GF) variation of the bicomponent nanoparticle is close to the model predictions in the high RH range. Finally, based on the positive correlation between particle volume and the gray intensity of SPRM-ARI, GF values can be obtained from the cube root of the gray intensity and the actual water content of single nanoparticles can then be derived.

Accurate Determination and Characterization of Gold Nanoparticles Based on Single Particle-Inductively Coupled Plasma-Mass Spectrometry

Abstract An accurate determination method for gold nanoparticles (AuNPs) number concentration and size was developed based on single particle-inductively coupled plasma-mass spectrometry (SP-ICP-MS). Influencing parameters such as different calculation methods of transport efficiency, dwell time, dispersing agent and injection mode were investigated and optimized. The transport efficiency has a greater impact on the accuracy of the measurement result, and it should be selected according to the measured target parameters. It was important to keep the stability of the transport efficiency and use the calibration standard calibrating during the measurement process. The dwell time directly affected the precision of result, and the data processing mode should be selected carefully according to the sample type, particle size and other properties. When the dwell time was 0.1 ms, the linear ranges of 30 nm and 60 nm AuNPs were 2–40 pg/g and 10–200 pg/g, respectively, the linear correlation coefficient was greater than 0.9998, the relative standard deviation was less than 3.80%. The detection limits of particle number concentration and particle size were 110 NPs/g and 9 nm, respectively. Four kinds of synthesized AuNPs and international pilot study sample were determined by the established method. The deviation of the number concentration in pilot study from the key comparison reference values was less than 5%. The results were equivalent and the expanded uncertainty was less than 15% (k = 2), which further verified the accuracy and applicability of the method.

A study of the evolution of nanoparticle dynamics in a homogeneous isotropic turbulence flow via a DNS-TEMOM method

In this article, a coupling of the direct numerical simulation (DNS) and the population balance modeling (PBM) is implemented to study the effect of turbulence on nanoparticle dynamics in homogenous isotropic turbulence (HIT). The DNS is implemented based on a pseudo-spectral method and the PBM is implemented using the Taylor-series expansion method of moments. The result verifies that coagulation due to turbulent shear force has a bigger impact on the evolution of number concentration, polydispersity, and average diameter of nanoparticles than Brownian coagulation in the HIT. The Reynolds number plays an important role in determining the number concentration, polydispersity, and average diameter of nanoparticles, and these quantities change more rapidly with an increase of Reynolds number. It is also found that the initial geometric standard deviation slows down the evolution of particle dynamics, but almost has no influence on the polydispersity of nanoparticles.

Nanoparticle Number Concentration in the Air in Relation to the Time of the Year and Time of the Day

The paper analyzes suspended particles number concentrations of 61 size fractions (184 nm to 17,165 nm) in the air at a traffic location. The average course of the individual fractions was analyzed at various intervals – daily, weekly, monthly and annually, in the period between 2017 and 2019. The data was then used to calculate the arithmetic mean for all the fractions (MS Excel, R) and then using a proprietary web application, heatmaps were constructed. The obtained results showed significant differences in both the annual and daily variation of number concentrations between the individual fractions differing in particle size. In the case of the annual variation, one can see a greater variability of smaller particles, which is most likely due to the source of the actual suspended particles. Meteorological and dispersion conditions are found as important factors for suspended particle concentrations. These can lead to significant differences from year to year. However, a comparison between 2018 and 2019 showed that even though the average absolute number concentrations can differ between years, the actual relative number concentrations, i.e., the ratios between the individual fractions remain very similar. In conclusion it can be said that the difference between the number concentration variation of the size fractions depends on both the actual pollution sources (especially in the long-term, i.e., the annual variation) and the actual size of the particles, which plays a role especially in the short-term (daily, weekly variation).

Nanoparticle exposure due to pyrotechnics during a football match

Abstract Use of pyrotechnic articles is a common, though forbidden practice at football matches. While the fans, especially the members of the ultras groups, view pyrotechnic displays as a part of their culture, these devices can be dangerous for the public. In addition to the risks of burning, hand flares and similar items release toxic combustion by-products, including particulate matter – inhaling of which is harmful both for the spectators and players. In order to assess the amounts and composition of the aerosol particles released at a typical event, we performed a study using both a scanning mobility particle sizer and a low-pressure cascade impactor. The number concentration of nanoparticles was clearly correlated with the burning events. Several elements were identified in the collected samples, including heavy metals, while the majority of the sample consisted of amorphous carbon. The nanoparticle number concentration increased up to 12-fold immediately after the beginning of the flares burning, with the largest contribution of particles 155 nm in diameter. The cumulative dose the players inhaled during the match was around 7 × 108 particles/kg, which is 300% higher than the dose one would get in a low-pollution environment. We discuss the results in view of similar pyrotechnical events, especially fireworks.

Nanoparticle number concentration measurements by multi-angle dynamic light scattering

We present the use of Multi-angle Dynamic Light Scattering (MADLS®) for the measurement of nanoparticle concentration. We describe the theory of the method and its application to nanoparticles made of gold, silica and polystyrene, with diameters ranging from 30 to 400 nm, and demonstrate some of the limitations with particles of sizes 500 nm and above. We evaluate the method accuracy, linearity and reproducibility, as well as the operational nanoparticle concentration and size range. We show that the concentration working range depends on the material’s optical properties, size and concentration. Here it is shown that the level of accuracy that can be expected for the concentration of particles is typically within 50% of the nominal value across a range of materials and sizes and, for some samples, within 20%. The repeatability of the measurements, in terms of relative standard deviation, is typically below 30%. A linearity of within 40% across a concentration range of 3·108 to 2·1011 mL−1 for concentration measurements was also demonstrated by using gold nanoparticles and gravimetric dilutions for method validation. Overall, we show that MADLS® is a rapid and straightforward method for the reproducible measurement of particle concentration, as well as size, requiring minimal sample preparation, without the need to calibrate using a pre-determined concentration series, and applicable to a broad range of materials. These features make it an ideal tool to support both development and quality control of particle materials for a broad range of applications.

The effect of water lubricant on reducing the generation of airborne wear particles from wheel–rail contacts under various train velocities

The effects of water lubricant to reduce airborne wear particles (AWPs) generation from wheel–rail contacts were investigated under three different train velocities using a twin-disk rig. Results indicated that the train velocity influenced generation trend, amount, and size distributions of nano- and micro-particles under dry and wet conditions. Water lubricant effectively reduced the number concentration (NC) of nano-particles, and the reduction increased with velocities. The NC of micro-particles generated under wet conditions was almost negligible for all tested velocities. Water vapors generated because of frictional heating significantly influenced the nano-particles NCs. Thus, water lubricants can effectively reduce the NCs of AWPs.