Number Size Distribution Research Articles

Characteristics of ultrafine particles emitted from 3D-pens and effect of partition on children's exposure during 3D-pen operation.

A three-dimensional (3D) printing pen is a popular writing instrument that uses a heated nozzle, and is similar to a 3D-printer. Processing thermoplastic filaments with a 3D-pen can emit ultrafine particles (UFPs). 3D-pen education sessions were held with "∏"-shaped partitions for the prevention of coronavirus disease (COVID-19). This study aimed to characterize UFP emissions from two types of 3D-pens and evaluate the influence of "∏"-shaped partitions on UFP exposure. Measurements of UFP emission rates and the size distribution of particles emitted from 3D-pens were conducted in a chamber (2.5m3 ). The partition's influence on UFP exposure was evaluated with and without a "∏"-shaped partition on a desk. A scanning mobility particle sizer (SMPS) and an optical particle spectrometer (OPS) were used to measure the particle number concentration (PNC) and size distribution. For both 3D-pen A and B, the average emission rates were statistically significantly highest for acrylonitrile butadiene styrene (ABS) filament (8.4×106 [3.4] particles/min and 1.1×106 [1.8] particles/min), followed by polylactic acid (PLA) (2.8×105 [1.5] particles/min and 4.8×104 [1.8] particles/min) and polycaprolactone (PCL) filaments (1.4×104 [2.8] particles/min and 2.0×104 [2.8] particles/min). For all filaments, particles in the Aitken mode (30-100nm) accounted for the highest proportion. In 3D-pen A, PNCs were higher with the partition than without it for ABS (1.2×106 [1.15] particles/cm3 vs. 1.4×105 [1.29] particles/cm3 ) and PLA (6.2×105 [1.38] particles/cm3 vs. 8.9×104 [1.12] particles/cm3 ), whereas for 3D-pen B, they were higher with the partition for ABS (9.6×105 [1.13] particles/cm3 vs. 4.9×105 [1.22] particles/cm3 ) only. With the partition installed, PNCs decreased to the background level after the operation ended, whereas it took 2-6min without the partition. However, the mass concentrations of PLA and PCL with 3D-pen A were not statistically significantly different with respect to the partition status. The use of 3D-pens with a partition can lead to high UFP exposure. Therefore, guidelines are required for the safe use of 3D-pens and partitions.

Hygroscopic growth and CCN activation of aerosols during Indian Summer Monsoon over a rain-shadow region

Hygroscopic growth factor and cloud condensation nuclei (CCN) activation properties of aerosols along with their physical and absorption properties were measured during the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) over a rain-shadow region, Solapur, India. The hygroscopicity of aerosols at both sub- and supersaturated regimes and the responsible factors are investigated during the Indian Summer Monsoon (ISM). During the intermittent rainy, wet, and cloudy days the total aerosol (≈ 966 cm−3), CCN (≈ 587 cm−3 at 0.4% supersaturation, S) number concentrations, and black carbon (≈ 482 ng m−3) mass concentrations were less, which increased to the mean values of ≈ 3754 cm−3, ≈ 974 cm−3, and ≈ 892 ng m−3, respectively during the dry and clear-sky period. Multiple mode aerosol number size distribution prevailed irrespective of the meteorological conditions, while a prominent nucleation mode was observed during the dry conditions. The nucleation mode was consistent from 09:00 hours local time (IST) during the dry conditions, apart from those associated with the local emissions during the sunset. The nucleation mode associated with the sharp enhancement in absorption Angstrom exponent after the BC peak during the early morning hours of dry days indicated the secondary organic aerosol formation. The hygroscopic growth factor measurements at 50 and 150 nm and the hygroscopicity parameter-ΚHTDMA values were spread over a wide range. But the mean and the median values were similar for both wet and dry periods. However, the hygroscopicity derived from CCN measurements-ΚCCN at 0.2 and 1.0% Ss were higher than the ΚHTDMA values. The high ΚCCN (≈ 0.44) during wet conditions reduced to ≈ 0.28 during the dry conditions for 1.0% S (corresponding to ~40 nm). The hygroscopicity and the CCN efficiency of aerosols were high during daytime and from midnight to sunrise for the dry and the wet periods, respectively.

Atmospheric particle number size distribution and size-dependent formation rate and growth rate of neutral and charged new particles at a coastal site of eastern China

Coastal new particle formation (NPF) may be complicated due to the influence of both continental and marine air masses. Here we presented the result of particle number size distribution and NPF event measurements at a coastal industrial park of eastern China from 2018 to 2019. The highest nucleation-mode particle number concentration (daytime maximum: 4.9 × 103 cm−3) and NPF frequency (8% of the observation days) were observed in the continental-marine air masses that originated from North China Plain and traveled along the coastline before arriving at the coastal site. The formation rates of 2 nm particles (J2) at this coastal site are similar to those reported in the urban environments around the world, probably due to the influence of local industrial emission. Ion to total particle number concentration ratios in 2–7 nm and 7–20 nm were 1.5% and 12%, respectively, during the NPF periods. Neutral new particle formation pathway thus dominated over ion-mediated pathway at this coastal site. Our observation also showed that number concentration and formation rate of neutral new particles decreased monotonically with particle size, while those of charged new particles increased with particle size. Such difference points to additional formation and loss mechanisms of charged particles, such as ion-aerosol attachment and ion-ion recombination in the atmosphere. The behavior of appearance time-based growth rates, however, are similar for neutral and charged particles.

Diffuse light around cities: New perspectives in satellite remote sensing of nighttime aerosols

Satellite remote sensing of nighttime aerosols in the lower atmosphere poses additional challenges in comparison with daytime sensing, due to the specific features of the available light sources and the different scattering geometries. In this work we develop a detailed quantitative model for the top-of-atmosphere radiance of the halos of diffuse light observed around cities in satellite nighttime imagery. It is shown that these scattered light distributions contain relevant information about the aerosol properties, and that under some basic assumptions they can be used to estimate them. We formalize the basis of a method for retrieving the aerosol particle size number distribution function based on inverting the angular dependence of the radiance detected in near-nadir remote sensing observations. The results stress the convenience of endowing future night Earth observation missions with enhanced angular detection capabilities.

Atmospheric transformation of urban particle number size distributions during the transport along street canyons as quantified by an aerosol sectional model

Ultrafine particles (UFP) are quickly transformed within a few 100 m distance to the source because of aerosol dynamic processes. In order to predict the transformation of particle number size distributions (PNSD) near major streets, we developed a sectional model that represents aerosol dynamics within an air parcel that is transported from a major street along a minor street into the urban background. Simplifying assumptions on the transport and transformation due to dilution, coagulation, deposition and condensation were introduced to allow fast prediction with a limited number of model parameters. Model predictions were compared to observed PNSDs from semi-mobile measurement campaigns along 200 m long transects in Berlin, Germany. The total number concentration (TNC) along the transects declined on average by 30% for the evaluated measurement runs. The model agreed well with the observed PNSDs (coefficient of determination, R2 = 0.94). The model was sensitive to the selection of a dilution parameter b (+8/-11% TNC change due to variation by factor 2) and friction velocity u∗ (up to 3% TNC change by replacing parameterized u∗ by constant values in a similar range), but almost not sensitive to the other parameters. According to the model, the dilution contributed the most to the TNC decline (approx. 73% after 200 m transport distance), followed by coagulation and deposition (13 and 14% contribution, respectively). Due to the low computational effort of the model, it may contribute to real-time forecasting of PNSDs near major streets and to determining short-term exposure to particles.

Characteristics of Aerosol Size Distributions and New Particle Formation Events at Delhi: An Urban Location in the Indo-Gangetic Plains

Accurate information about aerosol particle size distribution and its variation under different meteorological conditions are essential for reducing uncertainties related to aerosol-cloud-climate interaction processes. New particle formation (NPF) and the coagulation significantly affect the aerosol size distribution. Here we study the monthly and seasonal variability of aerosol particle size distribution at Delhi from December 2011 to January 2013. Analysis of aerosol particle size distribution using WRAS-GRIMM reveals that aerosol particle number concentration is highest during the post monsoon season owing to the effect of transported crop residue and biomass burning aerosols. Diurnal variations in number concentration show a bimodal pattern with two Aitken mode peaks in all the seasons. Monthly volume size distribution also shows bi-modal distribution with distinct coarse and fine modes. NPF events are observed less frequently in Delhi. Out of 222 days of WRAS data, only 17 NPF events have been observed, with higher NPF frequency during summer season. Growth rate of the nucleation mode of NPF events vary in the range 1.88–21.66 nm/h with a mean value of ∼8.45 ± 5.73 nm/h. It is found that during NPF events the Aitken and nucleation mode particles contribute more to the number concentration. Simultaneous measurement of UV flux and particulate matter (PM10and PM2.5) have also been done along with particle number size distribution measurement to understand the possible mechanisms for NPF events over the study location.

Number concentration and size distribution of soot aerosols of heptane fire at low pressures

SummaryThe number concentration and size distribution of soot aerosols are imperative parameters in fire detection which is closely related to safety management, risk assessment, and fire analysis. The experiment of n‐heptane pool fire is conducted in a pressure chamber which simulates the 101, 90.9, 80.8, 70.7, 60.6, and 50.5 kPa environments. The influence of air pressure on the number concentration and size distribution of soot aerosols is investigated. The DMS500 fast particulate analyzer is used to analyze the number concentration and size distribution of gas samples. Both the geometric mean diameter and count median diameter of smoke particles increases with pressure. A second‐order polynomial equation with correlation coefficient of 0.99 is fitted to the geometric mean diameter of particles against pressure. The particle number concentration is significantly decreased when pressure is reduced according to a linear relationship with correlation coefficient of 0.92. The environmental pressure puts influence on the soot optical properties that affect fire smoke detection technologies used in the regions of different altitudes or air pressures.

BIOPOLYMER FOOD COMPOSITIONS BASED ON CARAMELIZED HONEY, WAX AND PROPOLIS FOR PREVENTION OF PERIODONTOSIS

For the first time, the processes occurring during caramelization of honey are studied and the biochemical properties of the obtained substances are studied. Infrared spectra, humidity and viscosity were analyzed, the size and size distribution of nanoparticles, elemental composition, oxymethylfurfural content and diastase number of caramelized honey were studied. As a result of research, the difference between the sizes of nanoparticles of natural and caramelized honey was established: caramelized honey is characterized by much smaller (1.5–2.0 times) particle sizes than for natural bee honey. Smaller particle sizes of caramelized honey, after thermochemical treatment in the presence of specially selected catalysts, increase its biochemical activity.
 The paper also describes a new method of processing crystallized honey and the characteristics of the obtained liquid honey for a long shelf life (at least 1 year). It is shown that with the help of a new method of low-temperature isothermal accelerated processing in a microwave reactor MWR-SPR, it is possible to dissolve the crystallized honey to a liquid state. The proposed method reduces the time for the dissolution of honey in comparison with the known method of heat transfer by 250 times. The properties and structure of particles of crystallized and liquid honey after low-temperature, isothermal, accelerated processing with the help of microwave technology of ultrahigh frequencies at 50 °C, for 60’s are investigated. The number and particle size of pollen in honey is reduced by 10 times, and the size of the crystals of glucose and sucrose after processing is reduced by 2–5 times. The method of angular distribution of the laser beam shows a reduction of the average size of sugar macromolecules in the processed honey in 2 times, compared with crystallized honey.
 It is proved that the proposed low-temperature, isothermal, accelerated processing of honey in a microwave reactor helps to maintain a high diastase Gotha number – 10–11, and the content of hydroxymethylfurfural does not exceed 3–6 mg/kg of honey. The results of X-ray fluorescence spectroscopy confirm that the chemical and element-oxide composition of honey after treatment is almost unchanged. Analyzes of data on chemical and biological oxygen consumption show that in samples of liquid honey, after dissolution by the proposed method, the biochemical activity of honey is reduced only twice, which is much less than during the dissolution of honey by traditional heat transfer. All this has a positive effect on the stabilization of liquid honey after dissolution, on its stability during long-term (up to 1 year) storage. The chemical properties of wax, propolis, honey before and after the caramelization process have been studied. Based on the results obtained from caramelized honey, wax and propolis created a chewing gum with biologically active components for the prevention and treatment of periodontal diseases (gingivitis, periodontitis and periodontitis). Clinical studies using chewing gum based on honey, wax and propolis for the treatment of periodontal tacine in dentistry confirmed a positive effect in 72.5% of patients.

Seasonality of the particle number concentration and size distribution: a global analysis retrieved from the network of Global Atmosphere Watch (GAW) near-surface observatories

Abstract. Aerosol particles are a complex component of the atmospheric system which influence climate directly by interacting with solar radiation, and indirectly by contributing to cloud formation. The variety of their sources, as well as the multiple transformations they may undergo during their transport (including wet and dry deposition), result in significant spatial and temporal variability of their properties. Documenting this variability is essential to provide a proper representation of aerosols and cloud condensation nuclei (CCN) in climate models. Using measurements conducted in 2016 or 2017 at 62 ground-based stations around the world, this study provides the most up-to-date picture of the spatial distribution of particle number concentration (Ntot) and number size distribution (PNSD, from 39 sites). A sensitivity study was first performed to assess the impact of data availability on Ntot's annual and seasonal statistics, as well as on the analysis of its diel cycle. Thresholds of 50 % and 60 % were set at the seasonal and annual scale, respectively, for the study of the corresponding statistics, and a slightly higher coverage (75 %) was required to document the diel cycle. Although some observations are common to a majority of sites, the variety of environments characterizing these stations made it possible to highlight contrasting findings, which, among other factors, seem to be significantly related to the level of anthropogenic influence. The concentrations measured at polar sites are the lowest (∼ 102 cm−3) and show a clear seasonality, which is also visible in the shape of the PNSD, while diel cycles are in general less evident, due notably to the absence of a regular day–night cycle in some seasons. In contrast, the concentrations characteristic of urban environments are the highest (∼ 103–104 cm−3) and do not show pronounced seasonal variations, whereas diel cycles tend to be very regular over the year at these stations. The remaining sites, including mountain and non-urban continental and coastal stations, do not exhibit as obvious common behaviour as polar and urban sites and display, on average, intermediate Ntot (∼ 102–103 cm−3). Particle concentrations measured at mountain sites, however, are generally lower compared to nearby lowland sites, and tend to exhibit somewhat more pronounced seasonal variations as a likely result of the strong impact of the atmospheric boundary layer (ABL) influence in connection with the topography of the sites. ABL dynamics also likely contribute to the diel cycle of Ntot observed at these stations. Based on available PNSD measurements, CCN-sized particles (considered here as either >50 nm or >100 nm) can represent from a few percent to almost all of Ntot, corresponding to seasonal medians on the order of ∼ 10 to 1000 cm−3, with seasonal patterns and a hierarchy of the site types broadly similar to those observed for Ntot. Overall, this work illustrates the importance of in situ measurements, in particular for the study of aerosol physical properties, and thus strongly supports the development of a broad global network of near surface observatories to increase and homogenize the spatial coverage of the measurements, and guarantee as well data availability and quality. The results of this study also provide a valuable, freely available and easy to use support for model comparison and validation, with the ultimate goal of contributing to improvement of the representation of aerosol–cloud interactions in models, and, therefore, of the evaluation of the impact of aerosol particles on climate.

Packing properties and steady strength of cemented loose granular materials

We study samples composed of loose cemented assemblies of particles under isotropic compression and biaxial shearing by means of a discrete-element approach. Compression tests are undertaken by consolidation of grains initially not presenting contacts under varying level of cementation and increasing confining pressure. We find a nonlinear evolution of the solid fraction with pressure that is described using the evolution of granular connectivity and the collapse of pores under homogeneous load. The poral space is characterized in terms of probability of void size number and volume distribution which, surprisingly, can contain voids as 30 times the size of an average particle. Under steady flow, the shear strength turned out to evolve non linearly with the cementation level. For cementation strengths below the confining pressure, the cementation between particles has little effect upon macroscopic friction angle. For greater values of cementation, a rapid increase of macroscopic friction occurs despite a drop in grain connectivity. Macroscopic cohesion is, in turn, small when compared with the interparticle bonding strength for highly cemented samples. The increment of macroscopic strength is found to deeply depend on the anisotropy of contact forces despite a homogeneous distribution of contact orientations and lower connectivity for highly cemented samples.

Evaluation of exposure to nano-sized particles among transport and vehicle service workers.

Exposure to fine and ultrafine particles from transport processes is a main consequence of emissions from engines, especially those with self-ignition. The particles released in these processes are a source of occupational and environmental particles exposure. The aim of this study was to assess the fine and nano-sized particles emission degree during work connected with transport and vehicle servicing. The tests were carried out at 3 workplaces of vehicles service and maintenance (a car repair workshop, a truck service hall, and a bus depot) during 1 work day in each of them. Measurements were performed using the following devices: DISCmini meters, GRIMM 1.109 optical counter and the DustTrak monitor. The number, surface area and mass concentration, and the number size distribution were analyzed. The mean number concentration (DISCmini) increased during the analyzed processes, ranging from 4×104 p/cm3 to 8×104 p/cm3, and the highest concentration was found in the car repair workshop. The particles mean diameters during the processes ranged 31-47 nm, depending on the process. An increase in the surface area concentration value was observed in correlation with the particles number, and its highest concentration (198 m2/cm3) was found during work in the car repair workshop. The number size distribution analysis (GRIMM 1.109) showed the maximum value of the number concentration for particles sized 60 nm. The mean mass concentrations increased during the tested processes by approx. 40-70%, as compared to the background. According to the measurement results, all the workplaces under study constituted a source of an increase in all analyzed parameters characterizing emissions of nano-sized particles. Such working environment conditions can be harmful to the exposed workers; therefore, at such workplaces solutions for minimizing workers' exposure, such as fume hoods or respiratory protection, should be used. Med Pr. 2021;72(5):489-500.

Machine Learning Uncovers Aerosol Size Information From Chemistry and Meteorology to Quantify Potential Cloud‐Forming Particles

AbstractCloud condensation nuclei (CCN) are mediators of aerosol‐cloud interactions, which contribute to the largest uncertainty in climate change prediction. Here, we present a machine learning (ML)/artificial intelligence (AI) model that quantifies CCN from model‐simulated aerosol composition, atmospheric trace gas, and meteorological variables. Comprehensive multi‐campaign airborne measurements, covering varied physicochemical regimes in the troposphere, confirm the validity of and help probe the inner workings of this ML model: revealing for the first time that different ranges of atmospheric aerosol composition and mass correspond to distinct aerosol number size distributions. ML extracts this information, important for accurate quantification of CCN, additionally from both chemistry and meteorology. This can provide a physicochemically explainable, computationally efficient, robust ML pathway in global climate models that only resolve aerosol composition; potentially mitigating the uncertainty of effective radiative forcing due to aerosol‐cloud interactions (ERFaci) and improving confidence in assessment of anthropogenic contributions and climate change projections.

Passive Vaping from Sub-Ohm Electronic Cigarette Devices.

To investigate passive vaping due to sub-ohm electronic cigarettes (e-cigs), aerosol number size distribution measurements (6 nm–10 µm) were performed during volunteer-vaping sessions. E-liquids, with vegetable glycerin (VG) and propylene glycol (PG), with a VG/PG ratio of 50/50 (with nicotine) and 80/20 (without nicotine), were vaped with a double-coil, single aerosol exit hole at 25–80 W electric power, corresponding to 130–365 kW m−2 heat fluxes and with an octa-coil, four aerosol exit holes atomizers, at 50–150 W electric power, corresponding to 133–398 kW m−2 heat fluxes. At the lowest heat flux, lower particle number concentrations (NTot) were observed for the nicotine-liquid than for the nicotine-free liquid, also due to its higher content of PG, more volatile than VG. For the octa-coil atomizer, at 265 and 398 kW m−2, NTot decreased below the first-generation e-cig, whereas volume concentrations greatly increased, due to the formation of super micron droplets. Higher volume concentrations were observed for the 80/20 VG/PG liquid, because of VG vaporization and of its decomposition products, greater than for PG. For the double coil atomizer, increasing the electric power from 40 W (208 kW m−2) to 80 W (365 kW m−2) possibly led to a critical heat flow condition, causing a reduction of the number concentrations for the VG/PG 50/50 liquid, an increase for the 80/20 VG/PG liquid and a decrease of the volume concentrations for both of them. Coherently, the main mode was at about 0.1 µm on both metrics for both liquids. For the other tests, two main modes (1 and 2 µm) were observed in the volume size distributions, the latter becoming wider at 100 and 150 W (265 and 398 kW m−2), suggesting the increased emission of light condensable decomposition products. The lower aerosol emissions observed at 150 W than at 100 W suggest the formation of gas-phase decomposition products. The observation of low-count high-volume aerosols addresses the relevance of the volume metric upon measuring the second-hand concentration of the aerosols released by sub-ohm e-cigarettes.

Characterization of Gold Nanorods Conjugated with Synthetic Glycopolymers Using an Analytical Approach Based on spICP-SFMS and EAF4-MALS.

A new comprehensive analytical approach based on single-particle inductively coupled plasma-sector field mass spectrometry (spICP-SFMS) and electrical asymmetric-flow field-flow-fractionation combined with multi-angle light scattering detection (EAF4-MALS) has been examined for the characterization of galactosamine-terminated poly(N-hydroxyethyl acrylamide)-coated gold nanorods (GNRs) in two different degrees of polymerization (DP) by tuning the feed ratio (short: DP 35; long: DP 60). spICP-SFMS provided information on the particle number concentration, size and size distribution of the GNRs, and was found to be useful as an orthogonal method for fast characterization of GNRs. Glycoconjugated GNRs were separated and characterized via EAF4-MALS in terms of their size and charge and compared to the bare GNRs. In contrast to spICP-SFMS, EAF4-MALS was also able of providing an estimate of the thickness of the glycopolymer coating on the GNRs surface.

Response of particle number concentrations to the clean air action plan: lessons from the first long-term aerosol measurements in a typical urban valley in western China

Abstract. The strictest ever clean air action (CAA) plan has been implemented by the Chinese government since 2013 to alleviate the severe haze pollution. The PM2.5 mass concentration was found to largely be reduced in response to emission mitigation policies, but the response of particle number concentrations (PNCs) to CAA was less evaluated in the previous studies, which may be significantly different from PM2.5 mass due to newly formed particle impacts. In this work, the first in situ observation of particle number size distributions (PNSDs) during 2012–2019 in urban Lanzhou was used to analyze long-term PNC variations and CAA impacts. The average number of particles in nucleation (N13−25, particle number in the size range of 13–25 nm), Aitken (N25−100, particle number in the size range of 25–100 nm) and accumulation (N100−800, particle number in the size range of 100–800 nm) modes were respectively 2514.0, 10 768.7 and 3258.4 cm−3, and N25−100 accounted for about 65.1 % of total PNCs during the campaign. The k-means clustering technique was used to classify the hourly mean PNSDs into six clusters, and each cluster corresponded to a specific source and influencing factor. The polluted clusters governed the winter PNCs before 2016, and their occurrence was less and less frequent after 2016, which was largely dominated by reduction in primary emissions. However, the contribution of new particle formation (NPF) events to summer N13−25 decreased from 50 % to about 10 % during 2013 to 2015 and then increased to reach around 60 % in 2019. The trends of size-resolved PNCs for each cluster were quantified by Theil–Sen regression. The size-segregated PNCs exhibited downward trends for all clusters during 2012–2015, especially in spring. The annual relative slopes of spring PNCs varied from −54.7 % to −17.2 %, −42.6 % to −14.1 %, and −40.7 % to −17.5 % per year for 13–25, 25–100, and 100–800 nm size ranges, and the reduction in the polluted clusters was much larger than NPF clusters. The ultrafine particle number was increased, and the amplitude was much greater during 2016–2019. The annual relative slopes of N13−25 varied between 8.0 % in fall and 135.5 % in spring for the NPF cluster. In response to CAA, the increased daytime net radiation, higher ambient temperature and lower relative humidity at noon for NPF events also could partly explain the higher N13−25 induced by the more frequent nucleation events after 2016, especially in spring. The air masses were mainly from the adjacent regions of urban Lanzhou and less affected by long-range transport for NPF events, and thus the particles were not easily grown by coagulation during transport processes, which was helpful for the occurrence of NPF events. Therefore, some effective measures to cooperatively control particle number concentration and mass should be taken for the Chinese megacities.

Mesoscale variations of the chemical composition of submicron aerosols and its influence on the cloud condensation nuclei activation

Mesoscale variation of the chemical composition of submicron aerosol concentrations and their influence on cloud condensation nuclei (CCN) activation have been examined over a tropical coastal location in peninsular India during the winter season. The land-sea breeze circulation, boundary layer evolution, and photochemical processes significantly influence the diurnal variation of the aerosol chemical composition over the region. Broadly, the organic aerosols (mean ∼37.50 ± 27.00 μg m−3) dominated the submicron mass loading with a mass fraction (MF) of 0.66, followed by sulfate (∼10.92 ± 6.13 μg m−3; MF ∼0.19), ammonium (3.46 ± 1.71 μg m−3; MF∼0.06) and a small contribution from nitrate (1.7 ± 1.5 μg m−3; MF ∼0.03). The average mass concentration of organic carbon (OC) is 8.84 ± 6.42 μg m−3 with a mean organics/OC ratio of ∼3, indicating the presence of aged, highly oxidized organics. The diurnal variation of all the aerosol species, except sulfate, depicted daytime-low and nighttime-high. The photochemical formation of sulfate aerosols overwhelms the reduction in concentration due to boundary layer mixing and sea-land breeze circulation during the daytime. The decrease in the organics/sulfate ratio during the daytime has significant implications on the CCN concentration and its activation properties. The average CCN number concentration and activation ratio (ratio of CCN to total aerosol number concentration) at 0.38% supersaturation during the study period are ∼3756 ± 1609 cm−3 and 0.52 ± 0.17, respectively. The diurnal variation of CCN concentrations and activation ratio is distinctly different. The change in the mode diameter of the number size distribution between sea-land breeze was found to be less (∼8 nm) compared to the large variation in chemical composition. This suggested the importance of mesoscale variations of aerosols, especially the contrasting diurnal variation of organics and sulfate aerosols in CCN activation.

Long-term trend of new particle formation events in the Yangtze River Delta, China and its influencing factors: 7-year dataset analysis

To evaluate the influence of anthropogenic emission reductions since 2013 in China, a long-term trend analysis of the particle number size distribution (PNSD) and new particle formation (NPF) events in the Yangtze River Delta (YRD) region was conducted based on the PNSD measurement (diameter ranging from 3 to 850 nm) at the Lin'an (LAN) regional background station from 2013 to 2019. A modified Mann-Kendall test and a Theil-Sen estimator were used to calculate the overall trend of particle number concentrations in different modes and the relevant influencing factors. We observed a significant decreasing trend in the Aitken and accumulation mode number concentrations, with annual decrease rates of approximately 5.6% and 8.2%, respectively, resulting in an approximately 6.0% decline in total particles annually. However, the nucleation mode particle number concentration showed no significant trend from 2013 to 2016, but an increasing trend from 2016 to 2019, which was related to the NPF events occurrence frequency. The regional NPF events of “banana shape” accounted for an increasing fraction of all NPF events. As a key parameter influencing the NPF event, the condensation sink decreased by approximately 63% from 2013 to 2019. Moreover, the estimated sulfuric acid concentration decreased by approximately 50%, with a higher reduction rate occurring during 2013–2016 as result of the effective SO2 reduction. Surface meteorological factors (including the air temperature, relative humidity, air pressure, and wind) and the air masses origin were found to played minor roles in the long-term trend of NPF events. As PNSD and NPF events are closely related to changes in the particle emissions and regional air pollution levels, studies concerning PNSD and NPF are necessary to provide important information regarding air quality improvements and evaluating the efficacy of climate change mitigation strategies.

Seasonal variations of particle number concentration and its relationship with PM2.5 mass concentration in industrial-residential airshed

The smaller particles that dominate the particle number concentration (PNC) in the ambient air only contribute to a small percentage of particulate matter (PM) mass concentration although present in high particle number concentration. These small particles may be neglected upon assessing the health impacts of the PM. Hence, the knowledge on the particle number concentration size distribution deserves greater attention than the particulate mass concentration. This study investigates the measurement of the particle mass concentrations (PM2.5) and PNC of 0.27μm < Dp < 4.50μm during the southwest (SW), inter-monsoon (IM) and northeast (NE) monsoons in the industrial-residential airshed of Skudai, Johor Bahru, Malaysia. The PM2.5 mass concentrations and PNC were measured using a multi-channel GRIMM Environmental Dust Monitor (GRIMM EDM-SVC 365) equipped with a global positioning system. Diurnal variations, statistical analysis and regression plots were utilised from a six-month hourly data set to examine the patterns of the PNC size distributions and its relationships with the PM2.5 mass concentration. The overall mean PM2.5 mass concentration was 21.85μgm-3, with the 24h mean values of 26.80μgm-3, 26.08μgm-3 and 13.76μgm-3 for the SW, IM and NE monsoons, respectively. It was found that the hourly mean of PNC was recorded at the highest concentration during the SW monsoon (373.20 # cm-3). The particles in the accumulation mode (Dp < 1.0μm) were the prevalent form of the particle number concentration (94-98%). The scatter plots between the PM2.5 mass concentration and particle number size distribution showed that the PNC mode of 0.27 < Dp < 1.0μm has the highest correlation value of r2 = 0.87 due to the emission from the anthropogenic activities. The results of this study highlight the importance of the PNC measurement in the seasonal variations of the PM2.5 pollution, indicating the significance of the regional-scale emission control actions in the local air quality management.

Aerosol–Cloud Interaction at the Summit of Mt. Fuji, Japan: Factors Influencing Cloud Droplet Number Concentrations

To investigate interactions between aerosols and clouds, the size and number concentrations of the cloud condensation nuclei (CCN) and the cloud droplets (CDs) were measured at the summit of Mt. Fuji (altitude 3776 m), Japan. The CCN number concentrations (NCCN) are significantly higher in continental air masses than in air masses from the Pacific Ocean. The hygroscopicity parameter κ did not change much for different air mass origins, indicating that aerosol particles in the free troposphere are well mixed. Based on the CD number concentrations (NCD), the degree of supersaturation in the ambient air during the cloud-shrouded period was estimated to be 0.15% (25th percentile) to 0.44% (75th percentile). To evaluate factors influencing the NCD, measured NCD were compared to ones calculated based on the Köhler theory using aerosol number size distributions, κ, and the degree of supersaturation. The results showed that NCD could not be reproduced satisfyingly when the mean number size distribution or the mean effective supersaturation were used for the calculation. This study highlights the importance of obtaining information about the degree of supersaturation to predict NCD in the atmosphere.

Investigation of Particle Number Concentrations and New Particle Formation With Largely Reduced Air Pollutant Emissions at a Coastal Semi‐Urban Site in Northern China

AbstractTo better understand the responses of particle number concentrations (PNCs) and new particle formation (NPF) to the largely reduced air pollutant emissions in urban atmospheres, we investigated the particle number size distributions in Qingdao, a coastal megacity in northern China, during two separate periods, 2010–2012 and 2016–2018. The results show only an average of 5% decrease in the total PNCs in 2016–2018 relative to 2010–2012, although the PM2.5 mass concentration decreased by over 40%. Nucleation‐mode PNCs decreased by 20%, which is attributable to reductions in primary emissions from on‐road vehicles and secondary sources. Unexpectedly, the accumulation‐mode PNCs increased by 11% in 2016–2018 relative to 2010–2012. The SO2 concentrations strongly decreased by ∼60%, and the NPF frequencies slightly decreased from 34% in 2010–2012 to 25% in 2016–2018. However, there were no significant changes in the apparent new particle formation rate (FR) or net maximum increase in nucleation‐mode PNCs (NMINP). The increased concentrations of other precursors may substantially negate the effect of SO2 reduction, leading to the invariant FR and NMINP. The maximum sizes of grown new particles decreased by 50%; combined with the decreased NPF frequency, the contribution of grown new particles to accumulation‐mode PNCs expectedly decreased in 2016–2018 relative to 2010–2012. Alternatively, the increased accumulation‐mode PNCs in 2016–2018 mainly attribute to the enhanced primary combustion emissions excluding on‐road vehicle emissions. The increase in accumulation‐mode PNCs in 2016–2018 provides insights on the inter‐annual variation in satellite‐based cloud properties, which appeared insensitive to the large decrease in satellite‐based aerosol optical depth.