@article{mahant_iversen_kasparoglu_bilde_petters_2023, title={Direct measurement of the viscosity of ternary aerosol mixtures}, ISSN={["2634-3606"]}, DOI={10.1039/d2ea00160h}, abstractNote={The optical properties of particles change with change in their phase state. The optical change was exploited in this study to measure the transition temperature of sucrose, citric acid, and tartaric acid mixtures.}, journal={ENVIRONMENTAL SCIENCE-ATMOSPHERES}, author={Mahant, Sunandan and Iversen, Emil Mark and Kasparoglu, Sabin and Bilde, Merete and Petters, Markus D.}, year={2023}, month={Feb} }
 @article{kasparoglu_islam_meskhidze_petters_2022, title={Characterization of a modified printed optical particle spectrometer for high-frequency and high-precision laboratory and field measurements}, volume={15}, ISSN={["1867-8548"]}, DOI={10.5194/amt-15-5007-2022}, abstractNote={Abstract. The printed optical particle spectrometer (POPS) is a lightweight, low-cost instrument for measurements of aerosol number concentrations and size distributions. This work reports on modifications of the Handix Scientific commercial version of the POPS to facilitate its use in multi-instrument aerosol sampling systems. The flow system is modified by replacing the internal pump with a needle valve and a vacuum pump. The instrument is integrated into closed-flow systems by routing the sheath flow from filtered inlet air. A high-precision multichannel analyzer (MCA) card is added to sample the analog pulse signal. The MCA card is polled at 10 Hz frequency using an external data acquisition system and improves upon the count-rate limitation associated with the POPS internal data acquisition system. The times required to change the concentration between 90 % and 10 % and vice versa for a step change in concentration were measured to be 0.17 and 0.41 s at a flow rate of 5 cm3 s−1. This yields a sampling frequency of ∼ 1–2 Hz, below which the amplitude of measured fluctuations is captured with > 70 % efficiency. The modified POPS was integrated into the dual tandem differential mobility analyzer system to explore the coalescence of dimer particles. Results show that the pulse-height response increases upon dimer coalescence. The magnitude of the increase is broadly consistent with the change in light-scattering amplitude predicted by the T-matrix method. It is anticipated that this modified version of the POPS will extend the utilization of the technique for a range of field and laboratory applications.}, number={17}, journal={ATMOSPHERIC MEASUREMENT TECHNIQUES}, author={Kasparoglu, Sabin and Islam, Mohammad Maksimul and Meskhidze, Nicholas and Petters, Markus D.}, year={2022}, month={Sep}, pages={5007–5018} }
 @article{kasparoglu_perkins_ziemann_demott_kreidenweis_finewax_deming_devault_petters_2022, title={Experimental Determination of the Relationship Between Organic Aerosol Viscosity and Ice Nucleation at Upper Free Tropospheric Conditions}, volume={127}, ISSN={["2169-8996"]}, DOI={10.1029/2021JD036296}, abstractNote={This work presents measurements of the ice nucleating ability of secondary organic material recorded between −40 and −70°C and relative humidity with respect to ice (RHice) between 150% and 220%. For a subset of systems, temperature and humidity dependence of particle viscosity as well as dry glass transition temperature were characterized using the dual tandem differential mobility analyzer method. Eleven unique monoterpene, sesquiterpene and aromatic precursors were used to generate secondary organic material (SOM) using either an oxidation flow reactor (OFR) or an environmental chamber (EC). For the SOM for which viscosity was measured, the particle glass transition temperatures varied between 6 and 23°C (n = 8). Measurements were performed to verify that increased relative humidity did not plasticize the particles below −10°C at residence times similar to those in the ice nucleation instrument. No heterogeneous ice nucleation was observed at the ∼0.5% onset threshold for any of the materials generated. The ice nucleation occurs by the freezing of SOM solution droplets consistent with homogeneous freezing indicating that they form an aqueous solution, or the SOM particles required water saturation to freeze, indicating that they were hydrophobic. Experiments exploring the influence of functional groups and mass loading did not reveal any obvious influence of particle chemistry or generation conditions on the results. Close structural matches between known organic ice nucleating particles as precursor or formed products did not yield materials that promoted freezing. These experiments suggest that heterogeneous ice formation of glassy secondary organic materials is likely uncommon under upper free tropospheric conditions.}, number={16}, journal={JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES}, author={Kasparoglu, Sabin and Perkins, Russell and Ziemann, Paul J. and DeMott, Paul J. and Kreidenweis, Sonia M. and Finewax, Zachary and Deming, Benjamin L. and DeVault, Marla P. and Petters, Markus D.}, year={2022}, month={Aug} }
 @article{kasparoglu_wright_petters_2022, title={Open-hardware design and characterization of an electrostatic aerosol precipitator}, volume={11}, ISSN={["2468-0672"]}, DOI={10.1016/j.ohx.2022.e00266}, abstractNote={Electrostatic precipitators are devices that remove charged particles from an air stream. We present the design and characterization of an electrostatic precipitator that is intended to be incorporated into aerosol sampling equipment. Hardware and software components of the design are open, all components can be directly purchased from vendors, and the device can be assembled with standard tools. Generic components are used to allow the repurposing of parts for other uses. The computer-controlled high-voltage power supply box associated with the project can be used for other common high-voltage applications in Aerosol Science and Technology, such as data acquisition and control systems for scanning mobility particle sizers. Computational fluid dynamics simulations are used to quantify the 3D flow field. The transfer function associated with the partial transmission is characterized through modeling and experiments. The observed transfer function is unique but deviates from the ideal transfer function due to the distortion of the flow near the inlet and the outlet of the device. Singly charged particles up to 624 nm and 253 nm can be completely removed for 0.5 L min-1 and 1 L min-1, respectively. We anticipate that our device will increase the accessibility of the technique to a broader audience.}, journal={HARDWAREX}, author={Kasparoglu, Sabin and Wright, Timothy P. and Petters, Markus D.}, year={2022}, month={Apr} }
 @article{kasparoglu_li_shiraiwa_petters_2021, title={Toward closure between predicted and observed particle viscosity over a wide range of temperatures and relative humidity}, volume={21}, ISSN={["1680-7324"]}, DOI={10.5194/acp-21-1127-2021}, abstractNote={Abstract. Atmospheric aerosols can exist in amorphous semi-solid or glassy phase states whose viscosity varies with atmospheric temperature and relative humidity. The temperature and humidity dependence of viscosity has been hypothesized to be predictable from the combination of a water–organic binary mixing rule of the glass transition temperature, a glass-transition-temperature-scaled viscosity fragility parameterization, and a water uptake parameterization. This work presents a closure study between predicted and observed viscosity for sucrose and citric acid. Viscosity and glass transition temperature as a function of water content are compiled from literature data and used to constrain the fragility parameterization. New measurements characterizing viscosity of sub-100 nm particles using the dimer relaxation method are presented. These measurements extend the available data of temperature- and humidity-dependent viscosity to −28 ∘C. Predicted relationships agree well with observations at room temperature and with measured isopleths of constant viscosity at ∼107 Pa s at temperatures warmer than −28 ∘C. Discrepancies at colder temperatures are observed for sucrose particles. Simulations with the kinetic multi-layer model of gas–particle interactions suggest that the observed deviations at colder temperature for sucrose can be attributed to kinetic limitations associated with water uptake at the timescales of the dimer relaxation experiments. Using the available information, updated equilibrium phase-state diagrams (-80∘C<T<40∘C, temperature, and 0%<RH<100%, relative humidity) for sucrose and citric acid are constructed and associated equilibration timescales are identified.}, number={2}, journal={ATMOSPHERIC CHEMISTRY AND PHYSICS}, author={Kasparoglu, Sabin and Li, Ying and Shiraiwa, Manabu and Petters, Markus D.}, year={2021}, month={Jan}, pages={1127–1141} }
 @article{petters_kasparoglu_2020, title={Predicting the influence of particle size on the glass transition temperature and viscosity of secondary organic material}, volume={10}, ISSN={["2045-2322"]}, DOI={10.1038/s41598-020-71490-0}, abstractNote={Abstract Atmospheric aerosols can assume liquid, amorphous semi-solid or glassy, and crystalline phase states. Particle phase state plays a critical role in understanding and predicting aerosol impacts on human health, visibility, cloud formation, and climate. Melting point depression increases with decreasing particle diameter and is predicted by the Gibbs–Thompson relationship. This work reviews existing data on the melting point depression to constrain a simple parameterization of the process. The parameter $$\xi $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>ξ</mml:mi> </mml:math> describes the degree to which particle size lowers the melting point and is found to vary between 300 and 1800 K nm for a wide range of particle compositions. The parameterization is used together with existing frameworks for modeling the temperature and RH dependence of viscosity to predict the influence of particle size on the glass transition temperature and viscosity of secondary organic aerosol formed from the oxidation of $$\alpha $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>α</mml:mi> </mml:math> -pinene. Literature data are broadly consistent with the predictions. The model predicts a sharp decrease in viscosity for particles less than 100 nm in diameter. It is computationally efficient and suitable for inclusion in models to evaluate the potential influence of the phase change on atmospheric processes. New experimental data of the size-dependence of particle viscosity for atmospheric aerosol mimics are needed to thoroughly validate the predictions.}, number={1}, journal={SCIENTIFIC REPORTS}, author={Petters, Markus and Kasparoglu, Sabin}, year={2020}, month={Sep} }