Number Size Distribution Research Articles

Aerosol size distribution properties associated with cold-air outbreaks in the Norwegian Arctic

Abstract. The aerosol particles serving as cloud condensation and ice nuclei contribute to key cloud processes associated with cold-air outbreak (CAO) events but are poorly constrained in climate models due to sparse observations. Here we retrieve aerosol number size distribution modes from measurements at Andenes, Norway, during the Cold-Air Outbreaks in the Marine Boundary Layer Experiment (COMBLE) and at Zeppelin Observatory, approximately 1000 km upwind from Andenes at Svalbard. During CAO events at Andenes, the sea-spray-mode number concentration is correlated with strong over-ocean winds with a mean of 8±4 cm−3 that is 71 % higher than during non-CAO conditions. Additionally, during CAO events at Andenes, the mean Hoppel minimum diameter is 6 nm smaller than during non-CAO conditions, though the estimated supersaturation is lower, and the mean number concentration of particles that likely activated in-cloud is 109±61 cm−3 with no statistically significant difference from the non-CAO mean of 99±66 cm−3. For CAO trajectories between Zeppelin Observatory and Andenes, the upwind-to-downwind change in number concentration is the largest for the accumulation mode with a mean decrease of 93±95 cm−3, likely attributable primarily to precipitation scavenging. These characteristic properties of aerosol number size distributions during CAO events provide guidance for evaluating CAO aerosol–cloud interaction processes in models.

Aerosol particle number concentration, ultrafine particle number fraction, and new particle formation measurements near the international airports in Berlin, Germany – First results from the BEAR study

Studies revealed airports as a prominent source of ultrafine particles (UFP), which can disperse downwind to residential areas, raising health concerns. To expand our understanding of how air traffic-related emissions influence total particle number concentration (PNC) in the airport’s surrounding areas, we conduct long-term assessment of airborne particulate exposure before and after relocation of air traffic from “Otto Lilienthal” Airport (TXL) to Berlin Brandenburg Airport “Willy Brandt” (BER) in Berlin, Germany. Here, we provide insights into the spatial–temporal variability of PNC measured in 16 schools recruited for Berlin-Brandenburg Air Study (BEAR).The results show that the average PNC in Berlin was 7900 ± 7000 cm−3, consistent with other European cities. The highest median PNC was recorded in spring (6700 cm−3) and the lowest in winter (5100 cm−3). PNC showed a bi-modal increase during morning and evening hours at most measurement sites due to road-traffic emissions. A comparison between measurements at the schools and fixed monitoring sites revealed good agreement at distances up to 5 km. A noticeable decline in this agreement occurred as the distance between measurement sites increased. After TXL was closed, PNC in surrounding areas decreased by 30 %. The opposite trend was not seen after BER was re-opened after the COVID-lock-down, as the air traffic has not reached the full capacity yet. The analysis of particle number size distribution data showed that UFP number fraction exhibit seasonal variations, with higher values in spring and autumn. This can be explained by nucleation events, which notably affected PNC.The presented findings will play a pivotal role in forthcoming source attribution and epidemiological investigations, offering a holistic understanding of airports’ impact on airborne pollutant levels and their health implications. The study calls for further investigations of air-traffic-related physical–chemical pollutant properties in areas found further away (> 10 km) from airports.

Modelling particle number size distribution: a continuous approach

Abstract Particulate matter (PM) is well known to be detrimental to health, and it is crucial to apportion PM into the underlying sources to target policies. Particle number size distribution (PNSD) is the most accessible data to identify these sources, which provides information on the PM sizes. Here, we propose a new functional factor model for PNSD, which allows to disentangle PM into sources and contributions while considering the complex dependencies of the data across different sizes and periods. Through a simulation study, we show that this method is able to identify sources correctly, and we use it to analyse hourly PNSD data collected in London for 7 years, finding 6 well-defined sources. Our proposed methodology is fast, accurate, and reproducible.

Exploring the use of ground-based remote sensing to identify new particle formation events: A case study in the Beijing area

New Particle Formation (NPF) is an important process of secondary aerosol production in the atmosphere, which has significant impacts on the Earth's radiation balance, air quality, and climate change. In this study, we develop a method to identify NPF events based on ground-based remote sensing. We propose a proxy to characterize NPF events utilizing ground-based remote sensing of gaseous precursors and aerosol optical depth (AOD). This proxy is applied to identify the NPF events in Beijing in the winter of 2022 and tested by comparison with in-situ observations of aerosol particle number size distributions (PNSD) from SMPS. The comparison shows that the NPF events for regional nucleation can be identified effectively when the threshold for sulfur dioxide and organic gases (i.e. formaldehyde) are determined as 0.44 × 10−4 and 1.07 × 10−4. Based on these thresholds, the NPF events can be identified at a high percentage (84 %) compared with in-situ observations. The relationship between identification of NPF events and meteorological conditions shows that NPF events in Beijing winter occurred more frequently under weather conditions with north-west wind direction, high wind speed and low relative humidity.

Size distribution, sources and chemistry of ultrafine particles at Barcelona-El Prat Airport, Spain

The rapid expansion of the aviation sector raises concerns about air quality impacts within and around airports. Ultrafine particles (UFP, diameter < 100 nm) are of particular concern due to their potential adverse health effects. In this study, particle number concentrations (PNC), particle number size distribution (PNSD), and other ancillary pollutants such as particulate matter (PM), nitrogen oxides (NOX), black carbon (BC), sulfur dioxide (SO2), ozone (O3), carbon monoxide (CO) and benzene, as well as organic markers and trace elements (in quasi-UFP) were measured at Barcelona-El Prat Airport (80 m and 250 m from the main taxiway and runway). Comparisons were made with an urban background (UB) location, and source apportionment of PNSD was performed using Positive Matrix Factorization (PMF). PNC inside the airport was nine-fold higher than the UB, and fifteen-fold higher when considering only nucleation mode particles (< 25 nm). Six sources contributing to PNC were identified inside the airport: Taxiing (48.7 %; mode diameter = 17 nm), Industrial/Shipping (7.4 %; mode diameter = 35 nm), Diesel (3.9 %; mode diameter = 64 nm), Regional recirculation (1.1 %; mode diameter = 100 nm), Photonucleation (16.6 %; mode diameter = 13 nm) and Takeoff (18.5 %; mode diameter = 23 nm). Due to the measurement location and prevailing wind patterns, no significant contributions from landings were detected. Chemical analysis of quasi-UFP collected on Electrical Low-Pressure Impactor (ELPI + ) filters (stages 2 to 6: 17–165 nm) revealed higher concentrations (> 2-fold) of Fe, Al, Cr, Cu, Mo, Mn, Pb, Ti, and Sb at the airport compared to the UB, with Al exhibiting the most pronounced disparity. Generally, PAH levels were low at both sites, although concentrations were higher at the airport relative to the UB. Overall, this study provides a comprehensive understanding of UFP within a major European airport, identifying the different sources contributing to PNC and PNSD.

Comparison of aerosol number size distribution and new particle formation in summer at alpine and urban regions in the Guanzhong Plain, Northwest China

Ultrafine particles play a crucial role in understanding climate change, mitigating adverse health effects, and developing strategies for air pollution control. However, the factors influencing the occurrence and development of new particle formation (NPF) events, as well as the underlying chemical mechanisms, remain inadequately explained. This study compared number concentrations and size distributions of atmospheric ultrafine particles at Xi'an (urban area) and the summit of Mt. Hua (alpine region) in summer to investigate the NPF mechanism and particle growth in both clean and polluted areas of the Guanzhong Plain. The average particle number concentration in Xi'an was significantly higher than that at Mt. Hua. The diurnal variation of total particle number concentration differed between Xi'an and Mt. Hua indicating a divergence in influencing factors. The size distributions in Xi'an varied across different timescales and weather conditions, whereas Mt. Hua exhibited little variation. This stability at Mt. Hua is attributed to its cleaner background atmosphere and the steady influx of aging particles with larger diameters transported from the free atmosphere. In both areas, geometric mean diameters (GMDs) were inversely proportional to particle number concentrations suggesting that increase in particle numbers were primarily due to the generation of smaller particles. The potential governing factors for NPF events differed somewhat between the urban and mountainous stations. In the urban area, intense local stationary and mobile emission sources promoted the growth of newly formed nanoparticles, with ozone-oxidized condensable vapors serving as key precursors. In contrast, at the mountainous station, NPF process were significantly influenced by anthropogenic precursors from long-range transport and locally emitted biogenic organics. The rapid increase in ultrafine particle concentrations primarily poses serious health risks and degrades air quality in urban areas, while also contributing to climate-related effects in alpine regions.

Sectoral Size‐Resolved Particle Number Emissions With Speciation: Emission Profile‐Based Quantification and a Case Study in the Yangtze River Delta Region, China

AbstractSizes and number concentrations are critical parameters for the impact of atmospheric particles on climate and human health. However, comprehensive studies focusing on size‐resolved particle number (PN) emissions from various sectors are scarce. This study aims to fill this research gap by developing sectoral size‐resolved PN emissions for major species including sulfate, organic mass (OM), and black carbon (BC). The size‐resolved emission profiles derived from various measurements in the literature were integrated with a particle mass emission inventory (EI) for 13 major sectors in the Yangtze River Delta region of China as a case study. The particle number size distribution (PNSD) of emitted particles exhibited two distinct peaks: one at approximately 10 nm and the other in the range of 40–60 nm. The primary contributors to PN emissions in the region in 2017 were power plants, gasoline vehicles, diesel vehicles, and cooking sources. In terms of species, OM dominated PN emissions, followed by primary sulfate and then BC. A regional size‐resolved aerosol model employing the size‐resolved PN EI developed here (referred to as the BIN‐SPE experiment) provided reasonably accurate temporal variations of the total PN concentration and captured the PNSD within the size range of 10–300 nm. Uncertainty analysis of sectoral PN emissions across size ranges was carried out and the performance of the BIN‐SPE experiment was compared with those of three commonly used PN emission parameterizations. Our model evaluations highlight future needs for in‐depth investigations into more advanced size‐resolved emissions and secondary OM formation mechanisms.

The behaviour of charged particles (ions) during new particle formation events in urban Leipzig, Germany

Abstract. Air ions are electrically charged particles in air. They are ubiquitous in the natural environment and affect the Earth's radiation budget by accelerating the formation and growth of new aerosol particles. Despite this, few datasets exist exploring these effects in the urban environment. A neutral cluster and air ion spectrometer was deployed in Leipzig, Germany, to measure the number size distribution of charged particles from 0.8 to 42 nm, between 27 July and 25 August 2022. Following previous analyses, charged particles were classified into small (0.8–1.6 nm), intermediate (1.6–7.5 nm), and large (7.5–22 nm) fractions by mass diameter, and their mean concentrations (sum of positive and negative polarities) during the campaign were 405, 71.6, and 415 cm−3, respectively. The largest peaks in intermediate and large ions were explained by new particle formation (NPF), with intermediate ions correlating well with sulfuric acid dimer. Smaller morning and evening peaks were coincident with black carbon concentrations and attributed to primary emissions. NPF events, observed on 30 % of days, coincided with intense solar radiation and elevated sulfuric acid dimer. Small charged particles were primarily associated with radioactive decay and highest during the early hours, and they are unrelated to primary emissions or NPF. The apparent contributions of charged particles to 3 and 7.5 nm particle formation rates were 5.7 % and 12.7 %, respectively, with mean growth rates of 4.0 nm h−1 between 3–7.5 nm and 5.2 nm h−1 between 7.5 and 22 nm. The ratio of charged to total particle formation rates at 3 nm suggests a minor role for charged particles in NPF. We conclude that NPF is a primary source of &gt; 3 nm ions in our data, with primary emissions being the major source in the absence of NPF.

A comprehensive study on the validation and application of multi-lognormal distribution models for atmospheric particles

The particle number size distribution (PNSD) is crucial for evaluating air quality and mitigating environmental pollution, as particles of different sizes have diverse effects on human health and climate. However, obtaining a comprehensive understanding of PNSD is challenging due to its inherent complexities and variability. Multi-lognormal distribution models are employed to fit PNSD, as seen in climate models, but discrepancies between model fits and observed PNSD persist. This study adopts hourly data from 2017 to 2020 across eight monitoring sites in diverse environments—rural, urban, mountainous, and polar, and compares the observed PNDS with those simulated by multi-lognormal distribution models. The results demonstrated that the model generally achieved a high correlation with observed PNSD data (r2 > 0.75), effectively capturing key characteristics of nucleation and Aitken mode particles. However, the model had a tendency to overestimate the total number concentration by approximately 1.09 times, particularly noticeable under conditions of high concentrations of smaller particles. The model successfully represented prevalent bimodal size distribution patterns in urban areas with high ultrafine particle concentrations, though its performance was slightly less accurate in scenarios involving trimodal distributions. Despite these strong correlations and the model's ability to reflect diurnal and seasonal variations, which suggests its broad applicability and utility, there were notable limitations on smaller time scales and in specific particle size ranges. These limitations were particularly evident in capturing detailed phenomena relevant to new particle formation events, indicating areas where model refinement is necessary. The results highlighted the importance of investigating discrepancies between model predictions and actual observations, which is crucial for refining climate models that utilize PNDS. The uniform comparison facilitated a detailed exploration of particle properties from model results, offering deeper insights into aerosol behavior and its environmental impacts.

Comparative Analysis of Primary and Secondary Emission Mitigation Measures for Small-Scale Wood Chip Combustion

The objective of this study is to systematically investigate not only the influence of different additive types—beyond the much-considered case of aluminum-silicate-based additives—but also to carry out an additional comparison between primary and secondary emission mitigation measures during small-scale wood-chip combustion. Hence, combustion trials are realized within a 33-kW combustion plant. Pine wood chips additivated with 1.0 wt%a.r. of four additives have shown promising emission reduction effects in the past; namely kaolin (i.e., aluminum-silicate-based), anorthite (i.e., aluminum-silicate- and calcium-based), aluminum hydroxide (i.e., aluminum-based), and titanium dioxide (i.e., titanium-based). In addition to the primary mitigation measure (i.e., (fuel) additivation), an electrostatic precipitator (ESP) as a common secondary mitigation measure for total particulate matter (TPM) reduction is used for comparison. In addition to standard analyses (e.g., gravimetric determination of TPM emissions), an extended methodology (e.g., characterization of the elemental composition and ultrafine particle fraction of TPM emissions) is applied. The results show that the additivation of wood chips with kaolin and anorthite can lead to an operation of the combustion plant in compliance with the German legal TPM limit values by undercutting the absolute emission level achievable by the ESP. Additionally, kaolin and anorthite achieve significant reductions in carbon monoxide (CO) emissions, while kaolin simultaneously, and similarly to ESP, also leads to a shift in the particle size number distribution of PM emissions towards coarser particles. All additives show a significant reduction of potassium (K) emissions by the formation of high-temperature stable K compounds in the resulting ashes.

Chemically Resolved Respiratory Deposition of Ultrafine Particles Characterized by Number Concentration in the Urban Atmosphere.

Ultrafine particles (UFPs) dominate the atmospheric particles in number concentration, impacting human health and climate change. However, existing studies primarily rely on mass-based approaches, leading to a restricted understanding of the number-based and chemically resolved health effects of atmospheric UFPs. In this study, we utilized a high-mass-resolution single-particle aerosol mass spectrometer to investigate the online chemical composition and number size distribution of ultrafine, fine, and coarse particles during the summertime in urban Shenzhen, China. Human respiratory deposition dose assessments of particles with varying chemical compositions were further conducted by a respiratory deposition model. The results showed that during our observation, particles containing elemental carbon (EC) were the dominant components in UFPs (0.05-0.1 μm). Compared to fine and coarse particles, UFPs can deposit more deeply into the respiratory tract with a daily dose of ∼2.08 ± 0.67 billion particles. Among the deposited UFPs, EC-cluster particles constituted ∼85.7% in number fraction, accounting for a daily number dose of ∼1.78 billion particles, which poses a greater impact on human health. Simultaneously, we found discrepancies in the chemically resolved particle depositions among number-, surface area-, and mass-based approaches, emphasizing the importance of an appropriate metric for particle health-risk evaluation.

In chamber calibration and performance evaluation of air quality low-cost sensors

Assessing individual exposure to PM2.5 (particulate matter of aerodynamic diameter lesser than 2.5 μm) requires precise monitoring of PM2.5 concentrations at specific geographical and temporal scales. This demand is met globally by low-cost particulate matter sensors, although calibrating them is difficult. In this study, four low-cost PM sensors, Sharp GP2Y1010AU0F, Honeywell HPMA115S0-XXX, Plantower PMSA003-A, and Sensirion SPS30, were calibrated and tested using various aerosols. The calibration method has three steps: individual (considering each sensor independently to a single aerosol type; n = 1), combined (all sensors for a specific model together for a specific aerosol type; n = 4), and generic (all sensors for a given model together to all aerosols; n = 16). Sensor responses are processed using linear, quadratic, power-law, and artificial neural network (ANN) algorithms in each calibration stage. Performance metrics, including coefficient of determination (R2), mean absolute percentage error (MAPE), root mean square error (RMSE), and percentage coefficient of variation (% CV), were utilized for assessment. Amongst all the four tested sensors, the Sensirion SPS30 sensors gave the best performance with a minimum R2 value of 0.911 when calibrated with a generic ANN calibration algorithm. Also, the MAPE was less than 10 %, and the RMSE was less than 7 % when exposed to different particles. Sensirion SPS30 showed the lowest inter-sensor variability with % CV less than 6 %. Sensors identified monodisperse polystyrene latex (PSL) particle size in the investigation. Regardless of exposure to 0.3, 0.46, 0.60, or 1.0 μm PSL, the reported number size distribution for the PMSA003 sensor remained consistent and did not align with the results from Grimm. As the PSL size rose, the SPS30 size distribution changed towards larger particle sizes, although it did not always match Grimm data. As the PSL size increased, the sensor's PM1, PM2.5, and PM10 mass proportions altered.

Nanocellulose separation from barley straw via ultrasound-assisted choline chloride – Formic acid deep eutectic solvent pretreatment and high-intensity ultrasonication

The present study aims at investigating the application of ultrasound assisted choline chloride (ChCl) – formic acid (FA) deep eutectic solvent (DES) pretreatment of Barley straw. In addition, the efficiency of a wet grinding followed by high intensity ultrasound (HIUS) treatment for production of cellulose nanofibers (CNF) has been evaluated. The DES (using ChCl: FA at 1:9 M ratio) treatment at 45 kHz ultrasound frequency and 3 h of treatment duration resulted in 84.68 ± 1.02 % and 82.96 ± 0.79 % of lignin and hemicellulose solubilisation, respectively. The purification of DES treated solid residue resulted in cellulose with more than 90 % purity. Further, 10 min of wet grinding followed by 40 min of HIUS treatment resulted in more than 80 % nano-fibrillation efficiency. The produced CNF had diameters less than 100 nm in number size distribution and type I cellulose structure. This study confirmed that the developed process offers a sustainable method for producing nanocellulose from agricultural waste.

Characterization of PM2.5 emissions from on-road vehicles in the tunnel of a major Middle Eastern city

Traffic emissions are an important source of air pollution worldwide, but in the Middle East, this problem is exacerbated by weak or no enforcement of emission regulations. Comprehensive measurements of fine PM emission factors (EFs) from road transport in the region have not yet been conducted, but such data are necessary for quantitative assessments of the health impact of transport emissions in the region. To address this need, PM2.5 samples collected inside the Salim Slam tunnel in Beirut, Lebanon were analyzed for carbonaceous matter (organic carbon (OC) and elemental carbon (EC)), water-soluble ions, elements, and selected organic compounds. The OC/EC ratio was 1.8 for the total fleet and 2.6 for light-duty vehicles (LDV), in agreement with the dominant proportion of gasoline LDV in the Lebanese fleet. A Cu/Sb ratio of 4.2 ± 0.1 was observed, offering a valuable metric for detecting brake wear emissions in subsequent studies conducted in the region. The EFs of carbonaceous matter, elements and ions generally varied by a factor 0.1 and 10 in comparison to literature values, while those for alkanes and polycyclic aromatic hydrocarbons were similar to the upper values previously reported. The average number size distribution was characterized by a single mode around 35 nm. The particles number EF (for diameters between 10 and 480 nm) was within the range of 1014-1015 particles per kg of fuel. The chemical mass balance model showed an average contribution to EF of 62% from non-exhaust sources. This study highlights the need for more enforceable stringent vehicular regulations because of the local practices (i.e., removal of catalyst) and some EF values are very high compared to other studies/countries.

Variations in Cloud Concentration Nuclei Related to Continental Air Pollution Control and Maritime Fuel Regulation over the Northwest Pacific Ocean

Here, we compared the concentrations of cloud condensation nuclei (CCN) and particle number size distributions (PNSDs) measured during the transient period from the winter to the summer East Asian monsoon in 2021 with those in 2014 to explore possible responses to how CCN responds to upwind continental air pollutant mitigation and marine traffic fuel sulfur content (FSC) regulation over the northwest Pacific Ocean (NWPO). We also employed the Positive Matrix Factorization (PMF) analysis to apportion concentrations of CCN (Nccn) to different sources in order to quantify its source-specified responses to mitigation of air pollution during the transient period. Our results showed that (1) upwind continental mitigation likely reduced Nccn by approximately 200 cm−3 and 400 cm−3 at 0.2% and 0.4% supersaturation (SS), respectively, in the marine background atmosphere over the NWPO; (2) FSC regulation resulted in a decrease in Nccn at 0.4% SS by about 50 cm−3 and was nearly negligible at 0.2% SS over the NWPO. Additionally, a PMF-resolved factor, characterized by a dominant nucleation mode, was present only in 2014 and disappeared in 2021, likely due to the reduction. This estimation, however, suffered from uncertainties since seasonal changes were hard to be deducted accurately. PMF-resolved factors accurately represented Nccn in 80–90% of cases, but this accuracy was not observed in the remaining cases. Finally, an integrated analysis of satellite-derived cloud parameters and ship-based measurements indicated that the reduced Nccn over the NWPO might be co-limited with meteorological factors in forming cloud droplets during the transient period.

Investigations of airborne tire and brake wear particles using a novel vehicle design

Non-exhaust emissions have become an increasingly important issue as their levels continue to rise and the health effects of particulate matter (PM) are more widely discussed. To address this issue, a vehicle demonstrator with integrated emission reduction of tires and brakes was developed as part of the Zero Emission Drive Unit Generation-1 (ZEDU-1) project. This novel concept includes the removal of tire road wear particles (TRWP) with a strong ventilation/filtering system and an enclosed multi-disk brake, making it a suitable tool for the investigation of non-exhaust emissions. Particle number (PN) and particle size distribution (PSD) measurements down to 2.5 nm were performed on a chassis dynamometer and on a test track. Due to the low background concentrations on the chassis dynamometer, it is possible to distinguish between tire and brake wear and to characterize even a small number of particle emissions. It could be shown that about 30 % less particles are emitted by the vehicle, when using the novel multi-disk brake instead of the conventional brake. The highest TRWP emissions were collected during acceleration and harsh braking. Characterization of the collected particles using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) revealed diverse particle shapes and differences between particles generated on the dynamometer and on a test track.Graphical

Multi-process atmospheric particle number size distribution over the Bohai Sea: Insights from cruise and onboard unmanned aerial vehicle observations

A better understanding of the particle number size distribution aids to better assess the direct and indirect effects of particles on air quality and climate. In this study, particle number concentrations (PNCs) and size distribution along with chemical components, gaseous pollutants, and meteorological parameters were measured during a cruise campaign over the Bohai Sea. Four distinct periods were identified, showing significant impacts from continental outflows and ocean emissions on the particle number size distributions. Under the strong terrestrial pollution transport period, an obvious increase of PNCs below 1 μm was observed. The significant correlation between black carbon (BC) and PNCs in the size range of 0.35–1.0 μm suggested aging of aerosols during the long-range transport. An invaded dust pollution significantly reduced PNCs below 0.5 μm, while tripled the number concentration of particles larger than 0.5 μm. The ocean moisture facilitated the mixing between dust and secondary aerosols. An intense sea fog event observed during the cruise slightly increased PNCs smaller than 1 μm while decreasing larger ones. The correlations between PNCs below 0.5 μm and BC as well as SO2 demonstrated the impact of shipping activities on the formation of fresh particles. Aerosol vertical profiles in the marine boundary layer were measured by an unmanned aerial vehicle platform. The vertical patterns of particle number size distribution were largely governed by the origins of transported air masses and profiles of wind fields. Observations showed that the particle distribution in the lower marine boundary layer was typically inhomogeneous and rapidly evolving with time, highlighting the importance of strengthening the vertical observations of atmospheric parameters over the ocean.

Tribology and airborne particle emissions from grey cast iron and WC reinforced laser cladded brake discs

Laser cladding (LC) is a promising technique to overlay a protective coating on grey cast iron (GCI) brake discs to enhance the wear and corrosion resistance. This study utilized a pin-on-disc tribometer in an aerosol chamber to investigate the tribology and airborne particle emissions from tungsten carbides (WC) reinforced coating overlayed onto GCI substrate through laser cladding. Uncoated GCI brake discs served as reference material, while low-metallic (LM) and non-asbestos organic (NAO) brake pads were used as counterparts. The results indicate that LC coating exhibited slightly higher coefficient of friction and significantly lower wear than uncoated GCI discs. Abrasive wear is the dominant wear mechanism for both uncoated GCI brake discs and LC coatings. LC coatings substantially decreased the particle mass concentrations. All three friction pairs displayed a mass weighted size distribution with a major peak around 2–3 μm. The number size distribution was dominated by a mode below 1 μm. Emissions by number were generally low. Meanwhile, all three friction pairs emitted sheared off and agglomerated particles, with iron being the dominant element. Tungsten was identified in the particles emitted from LC coatings, indicating that the hard coating has a potential to wear off and become airborne particles.

In-depth characterization of exhaust particles performed on-board a modern cruise ship applying a scrubber

To comply with environmental regulations, ship operators may adopt exhaust after-treatment devices such as scrubbers or selective catalytic reduction (SCR). Beyond gaseous emission control, these technologies impact the exhaust particles emitted from marine engines to the atmosphere. This study characterizes comprehensively the chemical composition and physical properties of exhaust aerosol particles upstream and downstream a hybrid scrubber operating in open loop mode on-board a modern cruise ship. The study considers two engines, one equipped with SCR and both with scrubber, during engine load conditions of 75 % and 40 %, and the influence of marine gas oil (MGO) use in addition to heavy fuel oil (HFO). At least 4 different particle types were observed in the exhaust based on transmission electron microscopy (TEM) studies both upstream and downstream scrubber, and both scrubber and SCR affected the particle number size distribution (PSD). The geometric mean diameter (GMD) of the particles increased over scrubber both due to removal of nucleation mode particles and particle growth in the scrubber. The scrubber effectively decreased particle number (PN) and, also, non-volatile particles, but the effect depended on particle size and no significant decrease was observed in number of particles above 50 nm, typically comprising black carbon (BC) and in the case of HFO combustion, also asymmetrical metal containing particles. In addition to PN, concentrations of PAH compounds were reduced in the scrubber. The results may be further utilized when including the exhaust aerosol characteristics from ships applying scrubbers to emission inventories, as well as climate and air quality models.

Aerosol‐Cloud Interactions Near Cloud Base Deteriorating the Haze Pollution in East China

AbstractAtmospheric aerosols not only cause severe haze pollution, but also affect climate through changes in cloud properties. However, during the haze pollution, aerosol‐cloud interactions are not well understood due to a lack of in situ observations. In this study, we conducted simultaneous observations of cloud droplet and particle number size distribution, together with supporting atmospheric parameters, from ground to cloud base in East China using a high‐payload tethered airship. We found that high concentrations of aerosols and cloud condensation nuclei were constrained below cloud, leading to the pronounced “Twomey effect” near the cloud base. The cloud inhibited the pollutants dispersion by reducing surface heat flux and thus deteriorated the near‐surface haze pollution. Satellite retrievals matched well with the in situ observations for low stratus clouds, while were insufficient to quantify aerosol‐cloud interactions for other cases. Our results highlight the importance to combine in situ vertical and satellite observations to quantify the aerosol‐cloud interactions.