The free fall of a drop through gas loaded with solid particles gives rise to multiple physical interactions, which remain poorly documented, especially when the drop is no longer spherical. In particular, no model predicts the particle collection efficiency for drops undergoing deformations or oscillations. This study aims to contribute to this effort by investigating numerically the dynamics of water drops freely falling in air laden with dispersed solid particles for drop Reynolds and Weber numbers such that the drops do (or do not) deform or oscillate (e.g., Re=30, 70, 500, and 876). A Eulerian–Lagrangian framework is adopted. The drop internal and external flows are simulated with direct numerical simulation (DNS), and the dynamics of the liquid–gas interface are tracked using a combination of the volume of fluid (VOF) and level set methods; this approach predicts the interface dynamics in line with experimental data. The trajectories of solid particles are simulated using Lagrangian tracking and taking into account drag, gravity, and Brownian motion. For spherical drops with Reynolds numbers below 200, our methodology replicates previous results. In the presence of oscillations and/or deformations, the flow parameters of the two continuous phases are correctly predicted. The particle collection efficiency also follows the experimental trend, but the values differ significantly from measurements found in the literature. We therefore propose certain areas of improvement with the goal of obtaining better fits to the available experimental data.
The contributions and evolution of fine elemental particulate matter (PM) sources were investigated in the Marseille–Fos basin (south of France) based on a 1-year-long (January–December 2023) study using online X-ray fluorescence (Xact) PM1
The contribution of agricultural emissions of fine particulate matter (PM2.5) poses significant health and environmental challenges, particularly in the UK where intensive farming activities contribute to elevated pollutant levels. This contribution includes direct emissions and PM2.53). The study aims to analyse the impact of a series of mitigation measures through emission scenarios (low, medium, high uptake) on the dairy, pig, and poultry sectors in 2030, mainly focusing on NH3332.52.53-rich atmosphere reducing the impact of these reductions in NH32.532.52.532.52.52.52.52.5, as well as to improve our understanding of the chemical atmospheric processes involved in secondary inorganic aerosols.
Coastal aerosols are formed through the complex mixing between marine air masses and continental emissions, which originate from both natural and anthropogenic sources. The properties of coastal aerosols are decisive for their interaction with sunlight and their influence on clouds, as well as the potential health implications for the population in these areas. In this study, the aerosol properties and sources at Aarhus Bay, Denmark, were investigated by combining in situ aerosol light scattering and absorption with size distribution measurements and footprint analysis by FLEXPART. Our analysis demonstrates a considerable contribution of anthropogenic aerosols from both fossil fuel combustion and biomass burning, as well as periods with highly scattering aerosols. Furthermore, good agreement was found between in situ and modelled black-carbon data. Combining in situ measurements and FLEXPART analysis further evidenced a major impact of local emissions, as well as a few long-range transport intrusions.
Ultrafine particles play a crucial role in the atmosphere, both as a source of larger particles and as a factor influencing human health. We analysed hourly particle number size distributions collected during 2015–2021 from an urban background station in the Rhine-Main area in Germany, focusing on potential particle sources and multi-annual trends. The site is influenced by diffuse regional sources such as motor traffic and domestic heating, as well as Frankfurt Airport, located at a distance of 6 km. The average total particle number concentration (TNC, size range 10–500 nm) was 9.4 × 103 cm−3. TNC maxima were observed in diurnal cycles at 07:00, 13:00, and 21:00 UTC+1 (UTC+1 is used throughout the paper). The midday peak was more distinct during the warm season and dominated by nucleation mode particles (NUCs, 10–30 nm), suggesting photochemical particle formation as a source. When the wind was blowing from Frankfurt Airport, a 2.5-fold concentration average in NUCs was observed compared to other directions (11.2 × 103× 103 cm−3, 2015–2021). In 2020, during traffic restrictions related to the COVID-19 lockdown, TNC downwind of the airport was 40 %–60 % lower compared to the average of the prior 4 years. The overall trend analysis for 2015–2021 yielded consistent downward trends for TNC (−2 % yr−1), atmospheric particulate matter (PM10) mass (4 % yr−1), and nitrogen dioxide (NO2) (−5 % yr−1). While our observations of particle number size distributions show general similarities to other Central European observations, the effect of winds from Frankfurt Airport as a particle source is most prominently seen in the range 10–30 nm. The airport's role as a source of NUCs, and the rise in flights from 2015 to 2019 may be the cause of lower decline rates when compared to other locations.
Sub-10 nm aerosol particles play a critical role in the atmosphere through their involvement in new particle formation, a key process influencing the availability of cloud condensation nuclei. In recognition of their significance, international observation frameworks such as the Aerosol, Clouds and Trace Gases Research Infrastructure (ACTRIS) engage in the process of integrating their observations into standardized protocols. ACTRIS aims to enhance the understanding of atmospheric processes, including those related to particle dynamics and their interactions with clouds and climate through harmonized long-term observations. To evaluate the performance of current instrumentation for sub-10 nm particle measurements, as well as the procedures for doing so, in November 2023, the ACTRIS Cluster Calibration Center in Helsinki, Finland, held its first workshop on the intercomparison of instrumentation for sub-10 nm aerosol particle number size distribution measurements.In this workshop, three mobility-based systems (GRIMM PSMPS, TSI 1 nm SMPS and TSI 3938N56) and five activation-based systems (three Airmodus A11s and two Airmodus A12s) were evaluated. The focus lay on assessing their number concentration response and size-dependent detection efficiency – including the determination of the diameter with 50 % detection efficiency – and sizing accuracy. In addition to these parameters, the instruments were compared with each other while measuring aerosol particle number size distributions side by side from an aerosol chamber. Beyond the evaluation of instrument performance, the workshop aimed toAlthough this work highlights the key strengths of the different measurement techniques and instruments, several challenges remain. Mobility-based systems showed high sizing accuracy, especially for particles larger than 2 nm, while encountering challenges in measuring particles in the lower atmospheric concentration range. Activation-based systems proved more sensitive at lower particle number concentrations and particle sizes, with the drawback of slight unit-to-unit variability. Additionally, a systematic size shift was identified in aerosols generated by 4-way-cross glowing wire generator setups, indicating a need for further investigation on this effect and the development of calibration equipment in the sub-10 nm size range.
This study focuses on measuring the mass concentration of soot aggregates generated with a Mini-CAST burner. The experiments were performed in a test bench able to generate soot particles with different size distributions and different organic to total carbon (
Photoacoustic spectroscopy (PAS) has become a common method for measuring aerosol absorption and is one of the few techniques capable of directly measuring absorption by suspended aerosol particles at ambient concentrations. When multiple wavelengths are used, PAS provides a way of measuring the absorption Ångström exponent (AAE) and, when combined with a scattering or extinction method, provides a measure of the aerosol single-scattering albedo (SSA), and both AAE and SSA are important parameters in climate models. Despite this utility, few commercial PAS instruments are available, and no multi-wavelength commercial instruments are currently available. Thus, most extant PAS instruments are custom-built and therefore come with considerable cost and development time and require access to machine shops capable of fabricating the needed components. The goal of this work was to provide a blueprint for a low-cost, multi-wavelength PAS for measurement of the aerosol AAE both in the laboratory and in the field. In an effort to create an instrument with a low barrier to entry, we aim to use low-cost, readily available components and use open-source options wherever possible. In this paper, we present the SiMPLE-PAS, a single-pass, multi-wavelength, portable, and low-expense photoacoustic spectrometer that uses low-cost electronics and a 3D-printed cell to meet these design goals. The instrument has a total bill-of-materials cost on the order of USD 500. The instrument is, to the best of our knowledge, the first 3D-printed PAS for aerosols and likely the lowest-cost PAS to date. The instrument performed well in laboratory validation experiments and showed good agreement with measurements of aerosol absorption by the previously developed MultiPAS-IV instrument when co-located at the second Georgia Wildland Fire Simulation Experiment (G-WISE 2) during April 2025. The instrument shows competitive detection limits of 0.63, 1.99, and 0.55 Mm−1σ), respectively, which will allow it to measure both ambient and laboratory-generated aerosols. The SiMPLE-PAS therefore provides a low-cost, accessible photoacoustic spectrometer that offers to lower the barrier to entry for groups wishing to measure aerosol absorption, whether in the laboratory or in the field.