Source Of Particles Research Articles

Characterization of refractory aerosol particles collected in the tropical upper troposphere–lower stratosphere (UTLS) within the Asian tropopause aerosol layer (ATAL)

Abstract. Aerosol particles with diameters larger than 40 nm were collected during the flight campaign StratoClim 2017 within the Asian tropopause aerosol layer (ATAL) of the 2017 monsoon anticyclone above the Indian subcontinent. A multi-impactor system was installed on board the aircraft M-55 Geophysica, which was operated from Kathmandu, Nepal. The size and chemical composition of more than 5000 refractory particles/inclusions of 17 selected particle samples from seven different flights were analyzed by use of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) combined with energy dispersive X-ray (EDX) microanalysis. Based on chemical composition and morphology, the refractory particles were assigned to the following particle groups: extraterrestrial, silicates, Fe-rich, Al-rich, Hg-rich, other metals, C-rich, soot, Cl-rich, and Ca-rich. Most abundant particle groups within the refractory particles are silicates and C-rich (non-volatile organics). In samples taken above the tropopause, extraterrestrial particles are becoming increasingly important with rising altitude. The most frequent particle sources for the small (maximum in size distribution DP-max=120 nm) refractory particles carried into the ATAL are combustion processes at the ground (burning of fossil fuels/biomass burning) and the agitation of soil material. The refractory particles in the ATAL represent only a very small fraction (< 2 % by number for particles > 40 nm) of the total aerosol particles, which are dominated by species like ammonium, sulfate, nitrate, and volatile organics. During one flight, a large number of very small (DP-max=25 nm) cinnabar particles (HgS) were detected, which are supposed to originate from a ground source such as coal combustion or underground coal fires.

Simulation study of secondary electron multiplication on microwave dielectric window

The phenomenon of dielectric breakdown in microwave windows restricts the enhancement of power capacity in high-power microwave systems. This process starts with the secondary electron multiplication, which significantly influences the breakdown threshold. In this study, we developed 3D simulation models for rectangular, circular, and annular windows to examine the secondary electron multiplication on their surfaces using the particle-in-cell method. Through a comparative study, we assessed the effects of various input powers, initial emission current densities from particle sources, and magnetic fields. Our findings reveal that the initial field emission current density, which ranges from 10−9 to 109 μA/cm2, marginally affects electron multiplication. However, increased microwave power (with power density ranging from 0.1 to 18.75 MW/cm2) accelerates this multiplication. Strong magnetic fields and non-uniform electric fields further enhance the electron multiplication process.

Role of Iodine-Assisted Aerosol Particle Formation in Antarctica.

New particle formation via the ion-mediated sulfuric acid and ammonia molecular clustering mechanism remains the most widely observed and experimentally verified pathway. Recent laboratory and molecular level observations indicate iodine-driven nucleation as a potentially important source of new particles, especially in coastal areas. In this study, we assess the role of iodine species in particle formation using the best available molecular thermochemistry data and coupled to a detailed 1-d column model which is run along air mass trajectories over the Southern Ocean and the coast of Antarctica. In the air masses traversing the open ocean, ion-mediated SA-NH3 clustering appears insufficient to explain the observed particle size distribution, wherein the simulated Aitken mode is lacking. Including the iodine-assisted particle formation improves the modeled Aitken mode representation with an increase in the number of freshly formed particles. This implies that more particles survive and grow to Aitken mode sizes via condensation of gaseous precursors and heterogeneous reactions. Under certain meteorological conditions, iodine-assisted particle formation can increase cloud condensation nuclei concentrations by 20%-100%.

Modeling the drivers of fine PM pollution over Central Europe: impacts and contributions of emissions from different sources

Abstract. Fine particulate matter (PM2.5) is among the air pollutants representing the most critical threat to human health in Europe. For designing strategies to mitigate this kind of air pollution, it is essential to identify and quantify the sources of its components. Here, we utilized the regional chemistry transport model CAMx (Comprehensive Air Quality Model with Extensions) to investigate the relationships between emissions from different categories and the concentrations of PM2.5 and its secondary components over Central Europe during the period 2018–2019, both in terms of the contributions of emission categories calculated by the particle source apportionment technology (PSAT) and the impacts of the complete removal of emissions from individual categories (i.e., the zero-out method). During the winter seasons, emissions from other stationary combustion (including residential combustion) were the main contributor to the domain-wide average PM2.5 concentration (3.2 µg m−3), and their removal also had the most considerable impact on it (3.4 µg m−3). During the summer seasons, the domain-wide average PM2.5 concentration was contributed the most by biogenic emissions (0.57 µg m−3), while removing emissions from agriculture–livestock had the most substantial impact on it (0.46 µg m−3). The most notable differences between the contributions and impacts for PM2.5 were associated with emissions from agriculture–livestock, mainly due to the differences in nitrate concentrations, which reached up to 4.5 and 1.25 µg m−3 in the winter and summer seasons, respectively. We also performed a sensitivity test of the mentioned impacts on PM2.5 on two different modules for secondary organic aerosol formation (SOAP and VBS), which showed the most considerable differences for emissions from other stationary combustion (in winter) and road transport (in summer).

Effect of Relative Humidity on the Rate of New Particle Formation for Different VOCs

Atmospheric new particle formation (NPF) is an important source of aerosol particles and cloud condensation nuclei, which affect both climate and human health. In pristine environments, oxidation of biogenic volatile organic compounds (VOCs) is a major contributor to NPF. However, the impact of relative humidity (RH) on NPF from these precursors remains poorly understood. Herein, we report on NPF, as inferred from measurements of total particle number density with a particle diameter (dp) > 7 nm, from three VOCs (sabinene, α-terpineol, and myrtenol) subjected to dark ozonolysis. From a series of comparative experiments under humid (60% RH) and dry (~0% RH) conditions and a variety of VOC mixing ratios (ξVOC, parts per billion by volume, ppbv), we show varied behavior in NPF at elevated RH depending on the VOC and ξVOC. In general, RH-dependent enhancement of NPF at an ξVOC between <1 ppbv and 20 ppbv was observed for select VOCs. Our results suggest that gaseous water at particle genesis enhances NPF by promoting the formation of low-volatility organic compound gas-phase products (LVOCs). This is supported by measurements of the rate of NPF for α-pinene-derived SOA, where RH had a greater influence on the initial rate of NPF than did ξVOC and ξO3.

A traffic-induced shift of ultrafine particle sources under COVID-19 soft lockdown in a subtropical urban area

During the unprecedented COVID-19 city lockdown, a unique opportunity arose to dissect the intricate dynamics of urban air quality, focusing on ultrafine particles (UFPs) and volatile organic compounds (VOCs). This study delves into the nuanced interplay between traffic patterns and UFP emissions in a subtropical urban setting during the spring-summer transition of 2021. Leveraging meticulous roadside measurements near a traffic nexus, our investigation unravels the intricate relationship between particle number size distribution (PNSD), VOCs mixing ratios, and detailed vehicle activity metrics. The soft lockdown era, marked by a 20–27% dip in overall traffic yet a surprising surge in early morning motorcycle activity, presented a natural experiment. We observed a consequential shift in the urban aerosol regime: the decrease in primary emissions from traffic substantially amplified the role of aged particles and secondary aerosols. This shift was particularly pronounced under stagnant atmospheric conditions, where reduced dilution exacerbated the influence of alternative emission sources, notably solvent evaporation, and was further accentuated with the resumption of normal traffic flows. A distinct seasonal trend emerged as warmer months approached, with aromatic VOCs such as toluene, ethylbenzene, and xylene not only increasing but also significantly contributing to more frequent particle growth events. These findings spotlight the criticality of targeted strategies at traffic hotspots, especially during periods susceptible to weak atmospheric dilution, to curb UFP and precursor emissions effectively. As we stand at the cusp of widespread vehicle electrification, this study underscores the imperative of a holistic approach to urban air quality management, embracing the complexities of primary emission reductions and the resultant shifts in atmospheric chemistry.

Femtosecond Dynamics of Fast Electron Pulses in Relativistic Laser-Foil Interactions.

We report the femtosecond time-resolved dynamics of relativistic electron pulses in ultraintense laser-foil interactions, by characterizing the terahertz self-radiation with single-shot ultrabroadband interferometry. Experimental measurements together with theoretical modeling reveal that the electron pulses inherit the duration of the driving laser pulse. We also visualize the electron recirculation dynamics, where electrons remain trapped inside the self-generated electrostatic potential well and rebound back and forth around the thin foil for hundreds of femtoseconds. Our results not only demonstrate an insitu, real-time metrology scheme for electron bursts, but also have important implications for understanding and manipulating the time-domain properties of laser-driven particle and radiation sources.

First study using a fixed-wing drone for systematic measurements of aerosol vertical distribution close to a civil airport

A profound knowledge of pollutant emissions and transport processes is essential to better assess the impact on local air quality, which ultimately affects human health. This is of special importance in the proximity of airports, as flight activities are a major source of ultrafine aerosol particles (UFP) that are associated with adverse health effects. A quantification of the aerosol population in the horizontal and in particular in the vertical distribution has not been sufficiently characterized so far, but is of crucial relevance, as the atmospheric boundary layer (ABL) is strongly interacting with aerosols. For this purpose, the fixed-wing research drone called ALADINA (Application of Light-weight Aircraft for Detecting in-situ Aerosol) was operated at a distance of approximately 4 km downwind of the German airport Berlin Brandenburg (BER) on October 11–19, 2021. During the investigation period, 140 vertical profiles of different meteorological parameters and aerosol particle sizes were obtained on six measurement days between the surface and up to a maximum altitude of 750 m above ground level (a.g.l.). The investigations indicate several features: The stability of the ABL is a key characteristic for the vertical distribution of aerosol population with highest concentrations close to ground. Inversion layers further enhance horizontal transport so that airport pollutants can be moved to a further distance away. The airborne observations of total particle number concentration (TNC) coincide with ground-based data from fix-point sites. They show a high variability depending on the distance to the plume as well as upwind position and highest concentrations of TNC related to rush hours of airport operations.

Particle characterization in commercial buildings: A cross-sectional study in 40 offices in Singapore

There is a knowledge gap in understanding how existing office buildings are protecting occupants from exposure to particles from both indoor and outdoor sources. We report a cross-sectional study involving weekly measurements of size-resolved indoor and outdoor particle concentrations in forty commercial building offices in Singapore. The outdoor and indoor particles size distributions were single mode with daytime peak number concentrations at 36.5 nm and 48.7 nm. Outdoor concentrations were significantly greater than indoors for all particle diameters. Indoor particle concentrations were generally low due to: 1) relatively high indoor particle removal (IPR) rates; 2) low indoor source strengths; and 3) low indoor particle of outdoor proportion (IPOP). We found that the ventilation system type had a substantial effect on indoor particle levels, IPR and IPOP. Through linear mixed model analyses, we identified dependencies of IPR rates with the use of MERV13 filters in supply air and filter maintenance frequency, IPOP with the use of MERV13 filters in the fresh air and supply air ducts and low particle source strength with regular daily cleaning presumably due to dust reservoir removal. Lastly, the contribution of outdoor sources was mainly seen for ultrafine and fine particles but less pronounced for coarse particles. This study provided detailed understanding of particle exposure in building offices and their influencing factors, facilitating future research on health impact of particle exposures.

Likely Common Coronal Source of Solar Wind and 3He-enriched Energetic Particles: Uncoupled Transport from the Low Corona to 0.2 au

Parker Solar Probe (PSP) observations of a small dispersive event on 2022 February 27 and 28 indicate scatter-free propagation as the dominant transport mechanism between the low corona and greater than 35 solar radii. The event occurred during unique orbital conditions that prevailed along specific flux tubes that PSP encountered repeatedly between 25 and 35 Rs during outbound orbit 11. This segment of the PSP orbit exhibits almost stationary angular motion relative to the rotating solar surface, such that in the rotating frame, PSP’s motion is essentially radial. The time dispersion often observed in impulsive solar energetic particle (SEP) events continues in this case down to velocities including the core solar-wind ion velocities. Especially at the onset of this event, the 3He content is much larger than the usual SEP abundances seen in the energy range from ∼100 keV to several MeV for helium. Later in the event, iron is enhanced. The compositional signatures suggest this to be an example of an acceleration mechanism for generating the seed energetic particles required by shock (or compression) acceleration models in SEP events to account for the enrichment of various species above solar abundances in such events. A preliminary search of similar orbital conditions over the PSP mission has not revealed additional such events, although favorable conditions (isolated impulsive acceleration and well-ordered magnetic field connection with minimal magnetic field fluctuation) that would be required are infrequently realized, given the small fraction of the PSP trajectory that meets these observation conditions.

Comprehensive the seasonal characterization of atmospheric submicron particles at urban sites in the North China Plain

To comprehensively investigate the seasonal variations in submicron particles (PM1 = NR-PM1 + BC) composition, sources and chemical processes, an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), along with a multiangle absorption photometer (MAAP), was deployed to observe at urban sites in the North China Plain from October 1, 2015, to July 31, 2016. The PM1 average mass were 36.4 ± 39.0, 32.9 ± 20.7, 40.4 ± 52.4 and 99.0 ± 88.7 μg m−3 in spring, summer, autumn and winter, respectively. On the whole, the OA accounted for the largest component of PM1 during the four seasons, with the highest contribution in winter, accounting for 49% on average, followed by autumn (47%), spring (40%) and summer (31%). The secondary inorganic aerosol (SIA) mass concentration in summer was the lowest but contributed the most to PM1 in summer (62%), and it was higher than that in spring (46%), autumn (43%) and winter (41%). Positive matrix factorization (PMF) was used to differentiate the high-resolution mass spectra (HRMS) of organic aerosol (OA) into six factors, including two secondary OA (highly oxidized, low-volatility oxygenated organic aerosols (LV-OOA) and less oxidized, semi-volatile oxygenated OA (SV-OOA)) and four primary OA (including cooking-related OA (COA), hydrocarbon-like OA (HOA), biomass burning OA (BBOA) and coal combustion OA (CCOA)). OOA (LV-OOA + SV-OOA) exhibited the highest OA loading in summer (59%), while POA (CCOA + COA + HOA) exhibited the highest OA loading in winter (62%). The OA exhibited similar bimodal diurnal patterns during the four seasons, the nitrate and sulfate seasonal diurnal variations slightly differed, and the peak value occurred at night in winter and in the morning during the other seasons. The trend of the LV-OOA and SV-OOA diurnal variation in spring, autumn and winter appeared small difference, and the summer vary differently compared to other seasons. However, the diurnal mass concentration in winter was much higher than other seasons. The COA diurnal pattern peaked at noon and at night during the four seasons, corresponding to the peak hours of dining activities. The HOA, BBOA and CCOA seasonal diurnal patterns showed low concentrations during the daytime and high concentrations at night. OA on HPD was 6, 7 and 7 times higher than that on CD in spring, autumn and winter. The SIA concentration significantly increased on HPD in spring (69.3 μg m−3, 52%), autumn (80.6 μg m−3, 50%) and winter (82.4 μg m−3, 43%). The organic nitrate average mass concentrations were 0.6 ± 0.5, 0.7 ± 0.2, 0.8 ± 1.2 and 2.5 ± 2.3 μg m−3 in spring, summer, autumn and winter, respectively. The organic nitrate diurnal pattern appeared at night was higher than that during the daytime in spring, autumn and winter. The opposite diurnal pattern emerged in summer. The average mass concentration of polycyclic aromatic hydrocarbons (PAHs) during the entire observation period reached 73.2 ± 154.2 ng m−3, and the seasonal average mass were 30.4 ± 30.6, 10.7 ± 4.0, 40.5 ± 10.3 and 220.3 ± 246.7 ng m−3 in spring, summer, autumn and winter, respectively. The highest diurnal values in spring, summer, autumn and winter were 44.2, 11.7, 71.6 and 366.8 ng m−3, respectively.

The Etching Effect Methods in Registration Properties on CR-39 Nuclear Track Detector

In this work, we use three different etching techniques—water bath, microwaves, and hotplate stirrer devices—in an effort to confirm the optimal etching time and conditions for tracks in the CR-39 solid-state nuclear track detector following irradiation to an alpha particle source (241Am). The research shows that the water bath’s maximum track density is 57596 tracks/cm2, appearing at 90 and 150 minutes. On the other hand, the hotplate stirrer’s maximum track density is 28050 tracks/cm2, appearing at 90 and 150 minutes. The microwave is the best etching method since it generated the tracks (65076 tracks/cm2) in a relatively short amount of time (10 min). The computation of the etching parameters, which are the bulk etch rates (VB), track etch rate (VT) and track etch ratio (V), was investigate in the etching properties. The time for the appearance of all traces of the microwave device is at a time of 10 minutes, followed by a hotplate stirrer at a time of 90 minutes, then a water bath at a time of 120 minutes.

Measurement report: Insights into the chemical composition and origin of molecular clusters and potential precursor molecules present in the free troposphere over the southern Indian Ocean: observations from the Maïdo Observatory (2150 m a.s.l., Réunion)

Abstract. New particle formation (NPF) in the free troposphere (FT) is thought to be a significant source of particles over the oceans. The entrainment of particles initially formed in the marine FT is further suspected to be a major contributor to cloud condensation nuclei (CCN) number concentrations in the marine boundary layer (BL). Yet, little is known about the process and, more broadly, about the composition of the marine FT, which remains poorly explored due to access difficulties. Here we report measurements performed in April 2018 at the Maïdo Observatory with a nitrate-based chemical ionization atmospheric pressure interface time-of-flight mass spectrometer, which have allowed the first molecular-level characterization of the remote marine FT composition. A number of molecules and clusters were identified and classified into nine groups according to their chemical composition; among the identified species, the groups containing methanesulfonic acid (MSA) and C2 amines show signals that are on average significantly higher when the site is under conditions representative of the marine FT (compared to the BL). The correlation analysis revealed apparent connections between the signals of the identified compounds and several variables concurrently measured at the site (under FT conditions) or related to air mass history, suggesting that oxalic acid, malonic acid, and observed C2 amines could be of terrestrial origin, with, in addition, a possible marine source for oxalic acid and amines, while iodic acid, sulfur species, and maleic acid have a dominant marine origin. Identification of FT conditions at the site was based on the analysis of the standard deviation of the wind direction; this parameter, which can easily be derived from continuous measurements at the site, is shown in the first part of the study to be a relevant tracer when compared to predictions from the Meso-NH atmospheric model. Similar to other high-altitude sites, FT conditions are mainly encountered at night at Maïdo; therefore, the link to NPF could not be established, and further research is needed to assess the composition of precursors to nanoparticle formation in the marine FT.

Prediction model for vertical distribution of oil particles under thermal plume and displacement ventilation in a machining workshop

Oil particle concentrations exhibit an inhomogeneous distribution in large-space machining workshops with a displacement ventilation system. The inhomogeneous distribution can lead to variations in the required supply air volume used to control the indoor particle concentration at different heights. To rapidly calculate the particle concentration distribution in the vertical direction, this study established a zonal particle concentration prediction model based on the mass and energy balance by considering the interaction between the heat source thermal plume, wall thermal plume, and supply airflow. An experiment was conducted in a scaled chamber to validate the proposed prediction model. The result showed that the relative error between the prediction model and experiment ranged from −17% to 10%. A case study was performed to demonstrate the applicability of the prediction model to the control of a displacement ventilation system. Using the prediction model, the control system can maintain the particle concentration in the work area below 0.5 mg/m³with variable particle source emission rates and reduce the supply air volume by at least 24% and 55% compared with the variable and constant air volume systems, respectively, neither of which can address the inhomogeneous distribution of oil particle concentration. The prediction model can also be used for the design of displacement ventilation systems when the inhomogeneous particle concentration distribution is considerable.

Cometary outbursts in the Oort cloud

Comet nuclei in the outer Solar system are constantly irradiated by cosmic rays at low temperatures. Accumulated high concentrations of radicals can undergo fast recombination with significant heating of cometary surface layers. We present the model of comet activity at large heliocentric distances caused by the recombination of radicals. We found that the considered mechanism can cause activity of comets in distant regions of the Solar system, even at the Oort cloud distances. Outbursts in distant comet reservoirs can be a new source of dust and ice particles contributing to the recently discovered anomalous diffuse light in the cosmic extragalactic background optic light and the unexpectedly high flux of dust particles detected by the New Horizons dust counter at the edge of the Kuiper belt. The orbits of small-radii comets in the Oort cloud are highly influenced by cometary outbursts. This effect may account for the observed decrease in the number of small-radius long-period comets.

Amplifying nonresonant production of dark sector particles in scattering dominance regime

We investigate the enhancement of dark sector particle production within the scattering dominant regime. These particles typically exhibit a slight mixing with Standard Model particles through various portals, allowing for their generation through in-medium oscillation from Standard Model particle sources. Our analysis reveals that in the scattering dominance regime, with a significantly smaller scattering mean free path λsca compared to the absorption mean free path λabs, the nonresonant production of sterile states can experience an enhancement by a factor of λabs/λsca. This phenomenon is demonstrated within the context of kinetic mixing dark photon production at a reactor, precisely satisfying this condition. By incorporating this collisional enhancement, we find that the current sensitivity to the mixing parameter ε for dark photons in the TEXONO experiment can be significantly improved across a range spanning from tens of eV to MeV. This advancement establishes the most stringent laboratory constraint within this mass spectrum for the dark photon. Sterile neutrino production, however, does not exhibit such enhancement, either due to the failure to meet the scattering dominance criterion or the neutrino damping in resonant production. Published by the American Physical Society 2024

White Stork Pellets: Non-Invasive Solution to Monitor Anthropogenic Particle Pollution.

The present study applied a non-invasive method to analyse anthropogenic particles and prey items in white stork (Ciconia ciconia) pellets. Pellets (n = 20) were obtained from white stork nests during the 2020 breeding season from two sites in Croatia. In total, 7869 anthropogenic particles were isolated. The majority of particles were fragments, while previous studies on other birds often reported fibres. An ATR-FTIR polymer analysis detected glass and construction and building materials, as well as several compounds associated with plastic masses. Polymer investigation revealed the presence of dotriacontane and octacosane, which are by-products of polyethylene (PE) degradation and transformation. Additionally, the detection of vinylidene chloride (VDC) highlights the historical contribution of polyvinylidene chloride (PVDC) to plastic pollution. Significant variation in particle quantity and size between the sampling sites was detected, with larger particles found at sites associated with the metal mechanical engineering industry and agriculture. Prey assessment revealed chitin remains of large insects such as Orthoptera and Coleoptera. This research confirms the potential of pellet analysis as a valuable tool for assessing the presence of anthropogenic particles in the environment. However, further research is needed to fully understand the extent of particle ingestion, particle sources and potential impact.

Steady-State Ultracold Plasma Created by Continuous Photoionization of Laser Cooled Atoms.

In this Letter we discuss our approach that makes possible creation of the steady-state ultracold plasma having various densities and temperatures by means of continuous two-step optical excitation of calcium atoms in the magneto-optical trap. A strongly coupled ultracold plasma can be used as an excellent test platform for studying many-body interactions associated with various plasma phenomena. The parameters of the plasma are studied using laser-induced fluorescence of calcium ions. The experimental results are well described by a simple theoretical model involving equilibration of the continuous source of charged particles by the hydrodynamical ion outflux and three-body recombination. The ultracold plasma with the peak ion density of 2.7×10^{6} cm^{-3} and the minimum electron temperature near 2K has been prepared. Our steady-state approach in combination with the strong magnetic confinement of the plasma will make it possible to reach extremely strong coupling in such system.

Chemical characterization and sources of background aerosols in the eastern Mediterranean

Measurements of the composition of the gas and particulate phases were conducted from May 9 to June 4 of 2016 at the Finokalia (Greece) remote coastal site in the eastern Mediterranean, continuing the effort to track long term changes of the atmospheric chemical composition in the area. Finokalia is influenced by air masses arriving in the site from regional sources in Europe, Africa, and other locations. In this study, a series of instruments and analysis techniques were used for the first time at the Finokalia site to characterize the composition of the organic aerosol (OA). The PM1 was composed of ammonium sulfate/bisulfate (60%), followed by organics (35%) and black carbon (BC) (4%). The OA was highly oxidized with an average oxygen-to-carbon (O:C) ratio of 0.81. Source apportionment of high-resolution organic aerosol mass spectra via positive matrix factorization (PMF) identified four factors: less oxidized oxygenated organic aerosol (LO-OOA), more oxidized oxygenated organic aerosol (MO-OOA), marine-related oxygenated organic aerosol (marine-OOA) and hydrocarbon-like organic aerosol (HOA). The LO-OOA (O:C = 0.92) was the dominant factor for most of the campaign (51% of the PM1 OA), while the MO-OOA (O:C = 1.1) was responsible for 11% of the OA. The marine-OOA factor was also highly oxidized (O:C = 1.03), contributing on average 24% to the total OA and was found to be well correlated with sulfate (R2 = 0.83). The anthropogenic HOA factor (O:C = 0.36) was related to activities in the island of Crete. Its mass spectrum was quite similar (R2 = 0.86–0.95) to those of other HOA factors in the literature and its average concentration was 0.2 μg m−3 (14% of OA). High molecular weight compounds were found, suggesting the presence of oligomers in agreement with the presence of a highly oxidized quenching agent. Aromatic VOCs, like benzene, toluene, and xylenes were on average 0.17, 0.66 and 0.36 ppb, respectively with toluene concentrations indicating the presence of a local source despite the remote nature of the site. New particle formation (NPF) was observed during 26% of the days. The air masses during NPF events passed over the island of Crete and the Balkans and were characterized by a low condensation sink (5.9 ± 2.2 10−3 s−1). Nucleation mode particle concentrations during NPF days had an additional evening peak between 17:00 and 22:00, which was accompanied by an HOA peak implying the influence of a source of sub-25 nm particles in the extended area. These findings show that even a relatively remote site like Finokalia is occasionally affected by sources located tens of kilometers away, something that should be taken into account in the interpretation of past and future measurements in this location.

Connecting remote and in situ observations of shock-accelerated electrons associated with a coronal mass ejection

Context. One of the most prominent sources for energetic particles in our Solar System are huge eruptions of magnetised plasma from the Sun, known as coronal mass ejections (CMEs), which usually drive shocks that accelerate charged particles up to relativistic energies. In particular, energetic electron beams can generate radio bursts through the plasma emission mechanism, for example, type II and accompanying herringbone bursts. Aims. In this work, we investigate the acceleration location, escape, and propagation directions of various electron beams in the solar corona and compare them to the arrival of electrons at spacecraft. Methods. To track energetic electron beams, we used a synthesis of remote and direct observations combined with coronal modeling. Remote observations include ground-based radio observations from the Nançay Radioheliograph (NRH) combined with space-based extreme-ultraviolet and white-light observations from Solar Dynamics Observatory (SDO), Solar Terrestrial Relations Observatory (STEREO), and Solar Orbiter (SolO). We also used direct observations of energetic electrons from the STEREO and Wind spacecraft. These observations were then combined with a three-dimensional (3D) representation of the electron acceleration locations, including the results of magneto-hydrodynamic models of the solar corona. This representation was subsequently used to investigate the origin of electrons observed remotely at the Sun and their link to in situ electrons. Results. We observed a type II radio burst followed by herringbone bursts that show single-frequency movement through time in NRH images. The movement of the type II burst and herringbone radio sources seems to be influenced by regions in the corona where the CME is more capable of driving a shock. We found two clear distinct regions where electrons are accelerated in the low corona and we found spectral differences between the radio emission generated in these regions. We also found similar inferred injection times of near-relativistic electrons at spacecraft to the emission time of the type II and herringbone bursts. However, only the herringbone bursts propagate in a direction where the shock encounters open magnetic field lines that are likely to be magnetically connected to the same spacecraft. Conclusions. Our results indicate that if the in situ electrons are indeed shock-accelerated, the most likely origin of the in situ electrons arriving first is located near the acceleration site of herringbone electrons. This is the only region during the early evolution of the shock where there is clear evidence of electron acceleration and an intersection of the shock with open field lines, which can be directly connected to the observing spacecraft.