Electrodynamic balance measurements of thermodynamic, kinetic, and optical aerosol properties inaccessible to bulk methods

Abstract

Abstract. Measurements of a single, levitated particle in an electrodynamic balance are an established tool for deriving thermodynamic and material data such as density, refractive index and activities of components of an aqueous solution under supersaturated conditions, where bulk measurements are not possible. The retrieval relies on combining mass-to-charge data and size data from light scattering. Here, we use a combination of low- and high-resolution Mie resonance spectroscopy to obtain radius data, enabling an accurate size determination not only when the particle is in equilibrium, but also when it is out of equilibrium due to kinetic limitation of mass transport. With the data measured under non-equilibrium conditions, it is possible to retrieve the water diffusivity. A challenge is that the radius retrieval by comparing measured light scattering with Mie theory requires the knowledge of refractive index as a function of concentration. Here, we show an iterative retrieval of refractive index and size for compounds for which data cannot be obtained in the bulk either due to lack of sufficient amounts of sample or limited solubility. We demonstrate the measurement strategy and the retrieval of water activity, density, refractive index and water diffusivity for aqueous shikimic acid. Water diffusivity in concentrated shikimic acid decreases by 6 orders of magnitude at 250 K compared to that at room temperature.

The dynamics of SARS-CoV-2 infectivity with changes in aerosol microenvironment

“…To provide insight into the underlying mechanisms that drive the observed airborne loss of SARS-CoV-2 infectivity, the microphysical changes (depicted in SI Appendix , Fig. S1 A ) taking place in the droplets hosting the virus were explored in real time and in situ using the CK-EDB with a time resolution of <100 ms ( 38 , 41 – 45 ). For context, the phase changes that occur during the evaporation of aqueous sodium chloride at an RH below the efflorescence threshold are shown in SI Appendix , Fig.…”

“…Thus, an assessment of the viability of suspended microbes within droplets can be made after periods of suspension varying between less than 5 s to many hours. These longevity measurements can then be contextualized with detailed measurements of the dynamic changes in the physicochemical properties of droplets generated the exact same way in an instrument referred to as the comparative kinetic-electrodynamic balance (CK-EDB) ( 38 , 41 – 45 ). The CK-EDB uses the same piezoelectric droplet-on-demand dispensers as the CELEBS to generate droplets, with particles captured in the path of a laser within a flow of humidity and temperature-controlled air ( SI Appendix , Fig.…”

Water Uptake and Loss in Viscous Aerosol Particles with Concentration-Dependent Diffusivities

“…28,29,33−36 Across a range of atmospherically relevant temperatures and RHs, the diffusivity of the shikimic acid− water system has very strong concentration dependence. 34 Figure 3 shows the time-dependent radius of aqueous organic aerosol particles in response to several different stepwise changes in RH. In all calculations presented in this work for these systems, parameters for aqueous shikimic acid were taken from ref 34 and parameters for aqueous sucrose were taken from ref 12.…”

Carbon Dioxide Diffusivity in Single, Levitated Organic Aerosol Particles

“…The experimental setup used in our experiments has been previously described in-depth. 7 In brief, an electrically charged aqueous particle is injected into an electrodynamic balance (EDB) by a droplet-on-demand generator (Hewlett-Packard 51633A ink jet cartridge, filled with a diluted aqueous solution). This EDB is of the double design, 36 with a high AC voltage applied to two electrode rings and a DC voltage across hyperbolic end-caps generating an electric field to trap the particle.…”

“…At this angle, both transverse electric (TE) mode resonances and transverse magnetic (TM) mode resonances are measured one after the other to determine the refractive index and radius simultaneously with an accuracy of 0.005 in the refractive index and a corresponding accuracy of 2 nm in size. 7 (ii) Simultaneously, the backscatter signal from a broad-band LED centered around 640 nm is recorded using a spectrograph with a slow-scan back-illuminated CCD (charge-coupled device) array detector to follow the radius change of the particle. 37 In the experiments described in this work, we use a typical total gas flow of 40 sccm (humidified nitrogen gas) and control the total pressure inside the cell at 600 Torr.…”