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1. Microphysics regimes due to haze–cloud interactions: cloud oscillation and cloud collapse

   https://doi.org/10.5194/acp-25-3785-2025  

   Yang, Fan; Sadi, Hamed Fahandezh; Shaw, Raymond A; Hoffmann, Fabian; Hou, Pei; Wang, Aaron; Ovchinnikov, Mikhail (January 2025, Atmospheric Chemistry and Physics)

   Abstract. It is known that aqueous haze particles can be activated into cloud droplets in a supersaturated environment. However, haze–cloud interactions have not been fully explored, partly because haze particles are not represented in most cloud-resolving models. Here, we conduct a series of large-eddy simulations (LESs) of a cloud in a convection chamber using a haze-capable Eulerian-based bin microphysics scheme to explore haze–cloud interactions over a wide range of aerosol injection rates. Results show that the cloud is in a slow microphysics regime at low aerosol injection rates, where the cloud responds slowly to an environmental change and droplet deactivation is negligible. The cloud is in a fast microphysics regime at moderate aerosol injection rates, where the cloud responds quickly to an environmental change and haze–cloud interactions are important. More interestingly, two more microphysics regimes are observed at high aerosol injection rates due to haze–cloud interactions. Cloud oscillation is driven by the oscillation of the mean supersaturation around the critical supersaturation of aerosol due to haze–cloud interactions. Cloud collapse happens under weaker forcing of supersaturation where the chamber transfers cloud droplets to haze particles efficiently, leading to a significant decrease (collapse) in cloud droplet number concentration. One special case of cloud collapse is the haze-only regime. It occurs at extremely high aerosol injection rates, where droplet activation is inhibited, and the sedimentation of haze particles is balanced by the aerosol injection rate. Our results suggest that haze particles and their interactions with cloud droplets should be considered, especially in polluted conditions. 

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2. An experimentally validated model of diffusion charging of arbitrary shaped aerosol particles

   https://doi.org/https://doi.org/10.1016/j.jaerosci.2020.105678  

   Li, Li; Gopalakrishnan, Ranganathan (January 2021, Journal of aerosol science)

   Particle shape strongly influences the diffusion charging of aerosol particles exposed to bipolar/unipolar ions and accurate modeling is needed to predict the charge distribution of non-spherical particles. A prior particle-ion collision kernel β_i model including Coulombic and image potential interactions for spherical particles is generalized for arbitrary shapes following a scaling approach that uses a continuum and free molecular particle length scale and Langevin dynamics simulations of non-spherical particle-ion collisions for attractive Coulomb-image potential interactions. This extended β_i model for collisions between unlike charged particle-ion (bipolar charging) and like charged particle-ion (unipolar charging) is validated by comparing against published experimental data of bipolar charge distributions for diverse shapes. Comparison to the bipolar charging data for spherical particles shows good agreement in air, argon, and nitrogen, while also demonstrating high accuracy in predicting charge states up to ±6. Comparisons to the data for fractal aggregates reveal that the LD-based β_i model predicts within overall ±30% without any systematic bias. The mean charge on linear chain aggregates and charge fractions on cylindrical particles is found to be in good agreement with the measurements (~±20% overall). The comparison with experimental results supports the use of LD-based diffusion charging models to predict the bipolar and unipolar charge distribution of arbitrary shaped aerosol particles for a wide range of particle size, and gas temperature, pressure. The presented β_i model is valid for perfectly conducting particles and in the absence of external electric fields; these simplifications need to be addressed in future work on particle charging. 

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3. A phase separation inlet for droplets, ice residuals, and interstitial aerosol particles

   https://doi.org/10.5194/amt-15-3213-2022  

   Koolik, Libby; Roesch, Michael; Dameto de Espana, Carmen; Rapp, Christopher Nathan; Franco Deloya, Lesly J.; Shen, Chuanyang; Hallar, A. Gannet; McCubbin, Ian B.; Cziczo, Daniel J. (January 2022, Atmospheric Measurement Techniques)

   Abstract. A new inlet for studying the aerosol particles andhydrometeor residuals that compose mixed-phase clouds – the phaSeseParation Inlet for Droplets icE residuals and inteRstitial aerosolparticles (SPIDER) – is described here. SPIDER combines a large pumpedcounterflow virtual impactor (L-PCVI), a flow tube evaporation chamber, anda pumped counterflow virtual impactor (PCVI) to separate droplets, icecrystals (∼3–25 µm), and interstitial aerosolparticles for simultaneous sampling. Laboratory verification tests of eachindividual component and the composite SPIDER system were conducted.Transmission efficiency, evaporation, and ice crystals' survival weredetermined to show the capability of the system. The experiments show theSPIDER system can separate distinct cloud elements and interstitial aerosolparticles for subsequent analysis. As a field instrument, SPIDER will helpexplore the properties of different cloud elements and interstitial aerosolparticles in mixed-phase clouds. 

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4. Wildfire Smoke Observations in the Western United States from the Airborne Wyoming Cloud Lidar during the BB-FLUX Project. Part I: Data Description and Methodology

   https://doi.org/10.1175/JTECH-D-21-0092.1  

   Deng, Min; Wang, Zhien; Volkamer, Rainer; Snider, Jefferson R.; Oolman, Larry; Plummer, David M.; Kille, Natalie; Zarzana, Kyle J.; Lee, Christopher F.; Campos, Teresa; et al (May 2022, Journal of Atmospheric and Oceanic Technology)

   Abstract During the summer of 2018, the upward-pointing Wyoming Cloud Lidar (WCL) was deployed on board the University of Wyoming King Air (UWKA) research aircraft for the Biomass Burning Flux Measurements of Trace Gases and Aerosols (BB-FLUX) field campaign. This paper describes the generation of calibrated attenuated backscatter coefficients and aerosol extinction coefficients from the WCL measurements. The retrieved aerosol extinction coefficients at the flight level strongly correlate (correlation coefficient, rr > 0.8) with in situ aerosol concentration and carbon monoxide (CO) concentration, providing a first-order estimate for converting WCL extinction coefficients into vertically resolved CO and aerosol concentration within wildfire smoke plumes. The integrated CO column concentrations from the WCL data in nonextinguished profiles also correlate (rr = 0.7) with column measurements by the University of Colorado Airborne Solar Occultation Flux instrument, indicating the validity of WCL-derived extinction coefficients. During BB-FLUX, the UWKA sampled smoke plumes from more than 20 wildfires during 35 flights over the western United States. Seventy percent of flight time was spent below 3 km above ground level (AGL) altitude, although the UWKA ascended up to 6 km AGL to sample the top of some deep smoke plumes. The upward-pointing WCL observed a nearly equal amount of thin and dense smoke below 2 km and above 5 km due to the flight purpose of targeted fresh fire smoke. Between 2 and 5 km, where most of the wildfire smoke resided, the WCL observed slightly more thin smoke than dense smoke due to smoke spreading. Extinction coefficients in dense smoke were 2–10 times stronger, and dense smoke tended to have larger depolarization ratio, associated with irregular aerosol particles. 

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5. Modeling nanoparticle charge distribution in the afterglow of non-thermal plasmas and comparison with measurements

   https://doi.org/https://doi.org/10.1088/1361-6463/abf70c  

   Suresh, Vikram; Li, Li; Redmond Go Felipe, Joshua; Gopalakrishnan, Ranganathan (June 2021, Journal of physics)

   null (Ed.)

   Particle charging in the afterglows of non-thermal plasmas typically take place in a non-neutral space charge environment. We model the same by incorporating particle-ion collision rate constant models, developed in prior work by analyzing particle-ion trajectories calculated using Langevin Dynamics simulations, into species transport equations for ions, electrons and charged particles in the afterglow. A scaling analysis of particle charging and additional Langevin Dynamics calculations of the particle-ion collision rate constant are presented to extend the range of applicability to ion electrostatic to thermal energy ratios of 300 and diffusive Knudsen number (that scales inversely with gas pressure) up to 2000. The developed collision rate constant models are first validated by comparing predictions of particle charge against measured values in a stationary, non-thermal DC plasma from past PK-4 campaigns published in Phys. Rev. Lett. 93(8): 085001 and Phys. Rev. E 72(1): 016406). The comparisons reveal excellent agreement within ±35% for particles of radius 0.6,1.0,1.3 μm in the gas pressure range of ~20-150 Pa. The experiments to probe particle charge distributions by Sharma et al. (J. Physics D: Appl. Phys. 53(24): 245204) are modeled using the validated particle-ion collision rate constant models and the calculated charge fractions are compared with measurements. The comparisons reveal that the ion/electron concentration and gas temperature in the afterglow critically influence the particle charge and the predictions are generally in qualitative agreement with the measurements. Along with critical assessment of the modeling assumptions, several recommendations are presented for future experimental design to probe charging in afterglows. 

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