Source Of Particles Research Articles

Characteristics of pollutants emitted by motor vehicles and their impact on the environment and engine operation

Gaseous and solid pollutants (dusts) of atmospheric air have been defined. Dusts have been divided according to various criteria and their properties have been given. The sources and characteristics of anthropogenic and natural pollutants of atmospheric air have been presented. It has been shown that the main sources of anthropogenic pollutants, apart from industry, are motorization, and internal combustion engines of cars are a source of gaseous pollutants and solid particles, the emission of which has been significantly reduced. The originality of the article consists in conducting an extensive literature analysis and proving that the emission of "non-engine" pollutants in the form of dust from the wear of friction linings of brakes, clutches and from the wear of tires and roads, as well as mineral dust raised from the ground, is currently a greater threat to human health and the environment than engine emissions. The impact of particulate matter emissions from road transport and mineral dust, which is the basic component of road dust, on human health, vegetation and on the operation of engine and vehicle systems is presented.

Observing super-coarse carbonaceous aerosol particles containing chloride in a tropical savanna climate at an agro-forest site in Thailand.

Coarse aerosol particles containing chloride in tropical forests are significant for understanding biogeochemical cycles and atmospheric processes, with implications for environmental health and climate change mitigation. This study explored the sources of super-coarse carbonaceous aerosol particles containing chloride in a tropical savanna climate. Aerosol samples were collected from an agro-forest site in Thailand during the dry season and analyzed using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Fourier-transform infrared (FTIR) spectroscopy. By examining the morphology and elemental compositions of individual aerosol particles, along with employing Positive Matrix Factorization (PMF) and backward trajectory analysis, potential sources were identified. The findings revealed two primary sources for the super-coarse aerosol particles: a mixture of biomass burning smoke and inorganic salts (likely from saline soil and sea salt), as well as halophilic fungal spores. FTIR analysis indicated the presence of compounds linked to biomass burning and clay minerals, influenced by prevailing northeast and southeast winds. Recommendations for future research include continued monitoring, correlation with meteorological parameters, and the application of transmission electron microscopy (TEM) for more detailed visualization and confirmation of aerosol sources.

Source apportionment of particle number size distribution at the street canyon and urban background sites

Abstract. Particle size is one of the key factors influencing how aerosol particles affect their climate and health effects. Therefore, a better understanding of particle size distributions from various sources is crucial. In urban environments, aerosols are produced in a large number of varying processes and conditions. This study intended to develop the source apportionment of urban aerosols by utilising a novel approach to positive matrix factorisation (PMF). The particle source profiles were detected in particle number size distribution data measured simultaneously in a street canyon and at a nearby urban background station between February 2015 and June 2019 in Helsinki, southern Finland. The novelty of the method is combining the data from both sites and finding profiles for the unified data. Five aerosol sources were found. Four of them were detected at both of the stations: slightly aged traffic (TRA2), secondary combustion aerosol (SCA), secondary aerosol (SecA), and long-range-transported aerosol (LRT). One of the sources, fresh traffic (TRA1) was only detected at a street canyon. The factors were identified based on available auxiliary data. Additionally, the trends of the found factors were studied, and statistically significant decreasing trends were found for TRA1 and SecA. A statistically significant increasing trend was found for TRA2. This work implies that traffic-related aerosols remain important in urban environments and that aerosol sources can be detected using only particle number size distribution data as input in the PMF method.

Longevity of size-dependent particle removal performance of do-it-yourself box fan air filters.

Filtration performance of do-it-yourself (DIY) box fan filters deployed across a university campus was assessed over an academic year. Four DIY air filters were constructed from box fans and air filters with a minimum efficiency reporting value (MERV) of 13 and deployed in four spaces (two laboratories that include sources of particles and two offices). They were operated 9 hours daily with a programmable timer and were continuously monitored with power meters. Particle concentrations in the spaces were continuously monitored with low-cost nephelometers. The particle size dependent clean air delivery rate (CADR) and single pass filtration efficiency for each box was measured in a laboratory before deployment and every 10 weeks, for a total of five measurements over 40 weeks. We find that these DIY box fan filters maintain robust performance over time, with each air filter maintaining at least 60% of its initial CADR at the end of the 40 week study even with daily operation in environments with modest particle concentrations. CADR values for particles of 1.0-3.0 μm optical diameter averaged 34% higher than CADR values for 0.35-1.0 μm particles, aligning with MERV 13 filter size-dependent filtration expectations. Reductions in CADR over time were attributed to a reduction in filtration efficiency, likely due to a loss of filter electrostatic charge over time. There was no strong indication that increased resistance due to particle accumulation on filters appreciably decreased flow rates over time for any of the fans. The long-term robustness of DIY box fan air filters demonstrates their validity as a cost-effective, high performance, alternative to portable high efficiency particulate air (HEPA) filters.

Ice-nucleating particles active below −24 °C in a Finnish boreal forest and their relationship to bioaerosols

Abstract. Cloud properties are strongly influenced by ice formation; hence, we need to understand the sources of ice-nucleating particles (INPs) around the globe. Boreal forests are known as sources of bioaerosol, and recent work indicates that these dominate the INP spectra above −24 °C. To quantify the INP population at temperatures below −24 °C, we deployed a portable cloud expansion chamber (PINE) in a Finnish boreal forest from 13 March 2018 to 11 May 2018. Using the 6 min time resolution PINE data, we present several lines of evidence that INPs below −24 °C in this location are also from biological sources: (i) an INP parameterization developed for a pine forest site in Colorado, where many INPs were shown to be biological, produced a good fit to our measurements; a moderate correlation of INPs with aerosol concentration larger than 0.5 µm and the fluorescent bioaerosol concentration; (ii) a negative correlation with relative humidity that may relate to enhanced release of bioaerosol at low humidity from local sources such as the prolific lichen population in boreal forests; and (iii) the absence of correlation with ultra-fine particles (3.5 to 50 nm), indicating that new particle formation events are not sources of INPs. This study should motivate further work to establish whether the commonality in bioaerosol ice-nucleating properties between spring in Finland and summer in Colorado is more generally applicable to different coniferous forest locations and times and also to determine to what extent these bioaerosols are transported to locations where they may affect clouds.

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.

Traffic Intensity as a Factor Influencing Microplastic and Tire Wear Particle Pollution in Snow Accumulated on Urban Roads

Traffic-related roads are an underestimated source of synthetic particles in the environment. This study investigated the impact of traffic volume on microplastic (MP) and tire wear particle (TWP) pollution in road snow. An examination was conducted in a medium-sized city situated in northeastern Poland, known for being one of the cleanest regions in the country. MPs and TWPs were found at all 54 sites, regardless of the intensity of traffic. The average concentration for all samples was 354.72 pcs/L. Statistically significant differences were found between the average values of the particle concentration on low, medium, and heavy traffic roads, amounting to 62.32 pcs/L, 335.97 pcs/L, and 792.76 pcs/L, respectively. Within all three studied groups of roads, MPs and TWPs with the smallest size, ranging from 50 to 200 μm, were prevalent. In all of the studied groups of roads, four analyzed shapes of particles were found, with irregular fragments being the most abundant form (89.23%). The most frequently recorded color among the collected samples was black (99.85%), and the least frequently recorded color was blue, constituting only 0.01%. This study suggests that snow cover on the roads may act like a temporary storage of pollutants during winter particularly in the temperate climate zone and, after thawing can significantly increase the concentration of MPs and TWPs in surface waters. Possible measures to decrease the release of MPs and TWPs into the environment in the city may include reducing the traffic volume and speed, implementing street sweeping, utilizing filtration chambers, and installing stormwater bioretention systems or settling ponds.

Very Large and Long-lasting Anisotropies Caused by Sunward Streaming Energetic Ions: Solar Orbiter and STEREO A Observations

The anisotropy of energetic particles provides essential information to help resolve the underlying fundamental physics of their spatial distributions, injection, acceleration, and transport processes. In this work, we report an energetic ion enhancement that is characterized by very large and long-lasting anisotropies observed by STEREO A and Solar Orbiter, which are nearly aligned along the same nominal Parker spiral. This ion enhancement appears at the rising phase of a widespread solar energetic particle event that was associated with the farside coronal mass ejection on 2022 February 15. According to our analysis, the long-lasting anisotropy resulted from the continuous injection of energetic ions from a well-connected particle source located beyond the STEREO A’s orbit. Solar Orbiter also observed an interval of very large anisotropy dominated exclusively by sunward streaming ions but with the additional implication that it detected the very early phase of ion injections onto magnetic field lines that newly connected to the particle source, which is likely the first reported event of this kind. These results further illustrate how energetic particle anisotropy information, in particular from multiple observer locations, can be used to disentangle the sources and transport processes of energetic ions, even when their heliospheric context is not simple.

Dose increment in ultrashort particle irradiations via coherent stopping power

We present a relativistic self-consistent theory of the coherent stopping power (CSP) of ultradense charged particle beams propagating in a dense matter. CSP corresponds to a collective inelastic collision which adds to the ordinary stopping power of individual particles. Unlike the latter, which depends only on the particles' energy, CSP depends upon many more parameters such as the total charge of the ensemble and its charge density and shape. This paves the way for a broad variety of novel methods to tailor particle absorption and penetration in a dense matter. CSP losses can be explained both by collective excitations of single or multiple molecules and by the emission of coherent Cherenkov radiation. Here we demonstrate that the former mechanism is more relevant than the latter. We find that the coherent energy absorption of subpicosecond particle bunches in water occurs exciting a broad Debye process in the GHz range and an intermolecular stretching vibration mode in the THz region. We generalize the Bethe-Bloch stopping power formula to coherent effects including self-forces, dielectric screening, and absorption by the dense matter. For the sake of a self-consistent dynamical theory including phase space evolution, we have also generalized the Fermi-Eyges theory of particle diffusion to the presence of forces. Nonlinear dynamics is demonstrated, inducing nonlinear dose release, beam self-focusing, and self-enhancement of coherent losses. Given the advent of ultraintense particle sources and their use for biomedical and other relevant applications, our results may be of paramount importance for contemporary and future developments of science and technology. Published by the American Physical Society 2024

Measurement report: Contribution of atmospheric new particle formation to ultrafine particle concentration, cloud condensation nuclei, and radiative forcing – results from 5-year observations in central Europe

Abstract. As an important source of sub-micrometer particles, atmospheric new particle formation (NPF) has been observed in various environments. However, most studies provide little more than snapshots of the NPF process due to their underlying observations being limited in space and time. To obtain statistically relevant evidence on NPF across various environments, we investigated the characteristics of NPF based on a 5-year dataset of the German Ultrafine Aerosol Network (GUAN). The results were also compared with observations in previous studies, with the aim to depict a relatively complete picture of NPF in central Europe. The highest NPF occurrence frequency was observed in regional background sites, with an average of about 19 %, followed by urban background (15 %), low-mountain-range (7 %), and high Alpine (3 %) sites. The annual mean growth rate between 10 and 25 nm varied from 3.7–4.7 nm h−1, while the formation rate with same size range 10–25 nm from 0.4 to 2.9 cm−3 s−1. The contribution of NPF to ultrafine particles (UFPs) was about 13 %, 21 %, and 7 % for the urban background, regional background, and low mountain range, respectively. The influence of NPF on cloud condensation nuclei (CCN) number concentration and the aerosol extinction coefficient for NPF days was the highest in mountainous areas. These findings underscore the importance of local environments when assessing the potential impact of NPF on regional climate in models, and they also emphasize the usefulness of a long-term aerosol measurement network for understanding the variation in NPF features and their influencing factors over a regional scale.

Airborne fungal concentrations around the Modelo Callao Landfill

Non-hazardous waste generated in Metropolitan Lima and Callao is transported to the Modelo Callao landfill for safe disposal. The accumulation of waste constitutes a significant source of fungal particles released into the atmosphere, posing a potential health risk to nearby populations. The aim of this research was to evaluate the concentration of outdoor fungal particles, considering environmental conditions (temperature, relative humidity, wind speed, and direction) during summer and winter seasons in the 18 de octubre settlement and Chillón Avenue, areas located in the vicinity of the Modelo Callao Landfill in Ventanilla during 2022. The gravitational method was used for sampling. The highest concentrations were detected at 150 and 200 m from the landfill, where a kindergarten and a local park are located. Fifteen fungal genera were identified in both seasons. The predominant fungi were Aspergillus spp. (46.09 %), Penicillium spp. (23.29 %) and Alternaria spp. (11.33 %). The average concentrations during summer and winter were 297.21 CFU/m3 and 471.69 CFU/m3, respectively. Based on these findings, we recommend that residential areas be located beyond 200 m from the landfill to minimize exposure to fungal aerosols. Additionally, we propose the implementation of an action plan to improve air quality in the areas surrounding the final disposal infrastructure.

Characterization of highly radiating nitrogen-seeded H-mode plasmas in unfavorable BT at ASDEX Upgrade

Abstract The highly radiating nitrogen-seeded H-mode plasmas in unfavorable BT has been characterized in the ASDEX Upgrade tokamak (AUG). Three levels of nitrogen puffing rates have been injected into a fully detached H-mode plasma, which is run in lower single null configuration with the ion B × ∇ B drift away from the X-point. A cold ( ∼ 1 − 2 eV) highly radiating ( ∼ 13.0 MW m − 3 ) region forms close to the X-point immediately after nitrogen seeding, as evidenced by measurements of the divertor Thomson scattering (DTS) and the two-dimensional bolometry reconstructions. In addition, the radiator moves further upwards above the X-point along the separatrix at the high-field side (HFS) with increasing nitrogen puffing rates, as evidenced by the Absolute eXtended UltraViolet (AXUV) measurements. The formation of the highly radiating regime is closely correlated to the modifications of the divertor plasma conditions. Along the line of sight of the DTS measurement, the electron temperature reduces down to a few eV, which initials near the X-point and further extends to the HFS scrape-off layer (SOL) simultaneously with the upward movement of the radiator, however, the electron temperature sustains ( ∼ 30 − 50 eV) at the low-field side (LFS) SOL with slightly decreased electron density. The highly radiating regime shows LFS/HFS divertor asymmetry, in contrast to that for H-mode plasmas in favorable BT , suggesting that the drifts play an important role for the formation of the highly radiating X-point regime at AUG. The neutral particle flux increases significantly (factor of ∼ 2 ) in the private flux region, while it increases slightly ( < 20 % ) in the main chamber, thus suggesting an enhanced sub-divertor neutral compression with the formation of the highly radiating regime. Furthermore, a degradation of the pedestal electron density was observed with an enhancement of the electron temperature further inside the pedestal, and complete divertor detachment was achieved by nitrogen seeding with sustained plasma confinement. Finally, particle sources and flow patterns of deuterium and nitrogen ions have been analyzed by SOLPS-ITER modelling, confirming that the E × B drift plays an important role for the formation of the highly radiating regime in unfavorable BT at AUG.

A comprehensive analysis of new particle formation across the northwest Atlantic: Analysis of ACTIVATE airborne data

New particle formation (NPF) is a critical source of particles and cloud condensation nuclei, yet there are scarce vertically-resolved measurements addressing NPF across different seasons in marine regions. This study leverages a multi-season set of airborne data from the NASA ACTIVATE mission between 2020 and 2022 to examine NPF characteristics over the northwest Atlantic ranging from the polluted U.S. East Coast to as far downwind (>1000 km) as Bermuda. Using the number concentration ratio above 3 and 10 nm (N3:N10) as a NPF indicator, we observe the highest ratios in the coldest months and comparable ratios over Bermuda relative to the U.S. East Coast. Within seasons, the highest and lowest ratios are found immediately above cloud tops and at the lowest possible flight altitudes (∼150 m above sea level), respectively. The ratio of (N3-N10)/N3 ranges from 0.16 to 0.29 depending on altitude, proximity to clouds, and season. The N3:N10 and (N3-N10)/N3 ratios increase with altitude up to as high as 9 km, with a case study showing favorable conditions around relatively thicker and precipitating cloud systems presumably due to high actinic fluxes and reduced aerosol surface area. Regression modeling reveals that increased N3:N10 is influenced most by reductions in temperature, relative humidity, and aerosol surface area. This work emphasizes the importance of both NPF in remote marine regions like Bermuda and vertical heterogeneity that exists in its contribution to aerosol and cloud condensation nuclei number budgets.

Biological and dust aerosols as sources of ice-nucleating particles in the eastern Mediterranean: source apportionment, atmospheric processing and parameterization

Abstract. Aerosol–cloud interactions in mixed-phase clouds (MPCs) are one of the most uncertain drivers of the hydrological cycle and climate change. A synergy of in situ, remote-sensing and modelling experiments were used to determine the source of ice-nucleating particles (INPs) for MPCs at Mount Helmos in the eastern Mediterranean. The influences of boundary layer turbulence, vertical aerosol distributions and meteorological conditions were also examined. When the observation site is in the free troposphere (FT), approximately 1 in ×106 aerosol particles serve as INPs around −25 °C. The INP abundance spans 3 orders of magnitude and increases in the following order: marine aerosols; continental aerosols; and, finally, dust plumes. Biological particles are important INPs observed in continental and marine aerosols, whereas they play a secondary, although important, role during Saharan dust events. Air masses in the planetary boundary layer (PBL) show both enriched INP concentrations and a higher proportion of INPs to total aerosol particles, compared with cases in the FT. The presence of precipitation/clouds enriches INPs in the FT but decreases INPs in the PBL. Additionally, new INP parameterizations are developed that incorporate the ratio of fluorescent-to-nonfluorescent or coarse-to-fine particles and predict >90 % of the observed INPs within an uncertainty range of a factor of 10; these new parameterizations exhibit better performance than current widely used parameterizations and allow ice formation in models to respond to variations in dust and biological particles. The improved parameterizations can help MPC formation simulations in regions with various INP sources or different regions with prevailing INP sources.

Atmospheric Bases-Enhanced Iodic Acid Nucleation: Altitude-Dependent Characteristics and Molecular Mechanisms.

Iodic acid (IA), the key driver of marine aerosols, is widely detected within the gas and particle phases in the marine boundary layer (MBL) and even the free troposphere (FT). Although atmospheric bases like dimethylamine (DMA) and ammonia (NH3) can enhance IA particles formation, their different efficiencies and spatial distributions make the dominant base-stabilization mechanisms of forming IA particles unclear. Herein, we investigated the IA-DMA-NH3 nucleation system through quantum chemical calculations at the DLPNO-CCSD(T)/aug-cc-pVTZ(-PP)//ωB97X-D/6-311++G(3df,3pd) + aug-cc-pVTZ-PP level of theory and cluster dynamics simulations. We provide molecular-level evidence that DMA and NH3 can jointly stabilize the IA clusters. The formation rates of IA clusters initially decline before rising from the MBL to the FT, owing to variations in mechanism. In the MBL, IA-DMA nucleation predominates, while the contribution of IA-DMA-NH3 synergistic nucleation cannot be overlooked in polar and NH3-polluted regions. In the lower FT, IA-DMA-NH3 nucleation prevails, whereas in the upper FT, IA-NH3 nucleation dominates. The efficiency of IA-DMA-NH3 nucleation is comparable to that of IA-iodous acid nucleation in the MBL and sulfuric acid-NH3 nucleation in the FT. Hence, the IA-DMA-NH3 mechanism holds promise for revealing the missing sources of tropospheric IA particles.

Integrated modeling of anisotropic neutron yields of classical and spherical tokamaks

Estimations of counting rates of neutron spectrometers in experiments on controlled fusion with magnetic confinement, as well as calculations of energy resolved flux densities of fusion neutrons from plasma to the walls of a reactor require spatial integration of the local, usually anisotropic function of the neutron source. The integrated modeling consists of three main stages. First, sources of fast particles in beam- or wave-heated plasma are calculated. The next stage deals with spatial, energetic, and angular velocity distributions of plasma ions. Finally, double differential rate coefficients of nuclear fusion reactions are computed. This article describes calculations of spatial distributions of nuclear fusion reaction rates in classical and spherical tokamaks and the anisotropy of the neutron yield and spectra. The results are based on analytical formulas for energetic and angular distributions of the local source of fusion products in plasma. Examples of energetic spectral densities of neutron fluxes on first walls are presented, as well as energy resolved counting rates of collimated neutron spectrometers for perpendicular and tangential lines of sight.

Significant chlorine emissions from biomass burning affect the long-term atmospheric chemistry in Asia.

Biomass burning (BB) is a major source of trace gases and particles in the atmosphere, influencing air quality, radiative balance, and climate. Previous studies have mainly focused on the BB emissions of carbon and nitrogen species with less attention on chlorine. Reactive chlorine chemistry has significant effects on atmospheric chemistry and air quality. However, quantitative information on chlorine emissions from BB, particularly the long-term trend and associated atmospheric impacts, is limited both on regional and global scales. Here, we report a long-term (2001-2018) high-resolution BB emission inventory for the major chlorine-containing compounds (HCl, chloride, and CH3Cl) in Asia based on satellite observations. We estimate an average of 730 Gg yr-1 chlorine emitted from BB activity in Asia, with China contributing the largest share at 24.2% (177 Gg yr-1), followed by Myanmar at 18.7% and India at 18.3%. Distinct seasonal patterns and significant spatial and interannual variability are observed, mainly driven by human-mediated changes in agricultural activity. By incorporating the newly developed chlorine emission inventory into a global chemistry-climate model (CAM-Chem), we find that the BB-chlorine emissions lead to elevated levels of HCl and CH3Cl (monthly average up to 2062 and 1421 parts per trillion by volume (pptv), respectively), subsequently resulting in noticeable changes in oxidants (up to 3.1% in O3 and 17% in OH radicals). The results demonstrate that BB is not only a significant source of air pollutants but also of oxidants, suggesting a larger role of BB emissions in the atmospheric chemistry and oxidation process than previously appreciated. In light of the projected increase in BB activity toward the end of the century and the extensive control of anthropogenic emissions worldwide, the contribution of BB emissions may become fundamental to air quality composition in the future.

Пылегрязевые отложения как индикатор эколого-геохимического состояния территории арк­тического города

Urban surface deposited sediments are considered as an indicator of the ecological and geochemical state of the city of Murmansk. The authors have determined regularities that link mineral, chemical and granulometric composition of sediments into a single system; and characterized environmentally significant aspects of contemporary urban sediment genesis. It is shown that pollution and granulometric differentiation of sediments cause increased accumulation of some heavy metals in dust and mud sediments. The formation of sediment accumulations in relief depressions becomes a source of fine particles entering the atmosphere.

A Multi‐Scale Particle‐In‐Cell Simulation of Plasma Dynamics From Magnetotail Reconnection to the Inner Magnetosphere

AbstractDuring magnetospheric substorms, plasma from magnetic reconnection in the magnetotail is thought to reach the inner magnetosphere and form a partial ring current. We simulate this process using a fully kinetic 3D particle‐in‐cell (PIC) numerical code along with a global magnetohydrodynamics (MHD) model. The PIC simulation extends from the solar wind outside the bow shock to beyond the reconnection region in the tail, while the MHD code extends much further and is run for nominal solar wind parameters and a southward interplanetary magnetic field. By the end of the PIC calculation, ions and electrons from the tail reconnection reach the inner magnetosphere and form a partial ring current and diamagnetic current. The primary source of particles to the inner magnetosphere is bursty bulk flows (BBFs) that originate from a complex pattern of reconnection in the near‐Earth magnetotail at to . Most ion acceleration occurs in this region, gaining from 10 to 50 keV as they traverse the sites of active reconnection. Electrons jet away from the reconnection region much faster than the ions, setting up an ambipolar electric field allowing the ions to catch up after approximately 10 ion inertial lengths. The initial energy flux in the BBFs is mainly kinetic energy flux from the ions, but as they move earthward, the energy flux changes to enthalpy flux at the ring current. The power delivered from the tail reconnection in the simulation to the inner magnetosphere is W, which is consistent with observations.

How horizontal transport and turbulent mixing impact aerosol particle and precursor concentrations at a background site in the UAE

Abstract. The optical, physical, and chemical properties of aerosol particles have been previously studied in the United Arab Emirates (UAE), but there is still a gap in the knowledge of particle sources and in the horizontal and vertical transport of aerosol particles and their precursors in the area. To investigate how aerosol particle and SO2 concentrations at the surface responded to changes in horizontal and vertical transport, we used data from a 1-year measurement campaign at a background site where local sources of SO2 were expected to be minimal. The measurement campaign provided a combination of in situ measurements at the surface and the boundary layer evolution from vertical and horizontal wind profiles measured by a Doppler lidar. The diurnal structure of the boundary layer in the UAE was very similar from day to day, with a deep, well-mixed boundary layer during the day transitioning to a shallow nocturnal layer, with the maximum boundary layer height usually being reached around 14:00 local time. Both SO2 and nucleation-mode aerosol particle concentrations were elevated for surface winds coming from the east or western sectors. We attribute this to oil refineries located on the eastern and western coasts of the UAE. The concentrations of larger cloud condensation nuclei (CCN)-sized particles and their activation fraction did not show any clear dependence on wind direction, but the CCN number concentration showed some dependence on wind speed, with higher concentrations coinciding with the weakest surface winds. Peaks in SO2 concentrations were also observed despite low surface wind speeds and wind directions unfavourable for transport. However, winds aloft were much stronger, with wind speeds of 10 m s−1 at 1 km common at night and wind directions favourable for transport; surface-measured concentrations increased rapidly once these particular layers started to be entrained into the growing boundary layer, even if the surface wind direction was from a clean sector. These conditions also displayed higher nucleation-mode aerosol particle concentrations, i.e. new particle formation events occurring due to the increase in the gaseous precursor.