Mass-mobility characterization of flame-made ZrO2 aerosols: Primary particle diameter and extent of aggregation

[Display omitted] ► Generation of ZrO2 nanoparticles by scalable spray combustion. ► Rapid characterization by mass-mobility measurements with APM–DMA. ► Online determination of primary particle diameter and number in agglomerates. ► Good agreement with ex situ BET measurements and TEM image counting. ► Mass-mobility measurements reveal the degree of aggregation. Gas-borne nanoparticles undergoing coagulation and sintering form irregular or fractal-like structures affecting their transport, light scattering, effective surface area, and density. Here, zirconia (ZrO2) nanoparticles are generated by scalable spray combustion, and their mobility diameter and mass are obtained nearly in situ by differential mobility analyzer (DMA) and aerosol particle mass (APM) measurements. Using these data, the density of ZrO2 and a power law between mobility and primary particle diameters, the structure of fractal-like particles is determined (mass-mobility exponent, prefactor and average number, and surface area mean diameter of primary particles, dva). The dva determined by DMA–APM measurements and this power law is in good agreement with the dva obtained by ex situ nitrogen adsorption and microscopic analysis. Using this combination of measurements and above power law, the effect of flame spray process parameters (e.g., precursor solution and oxygen flow rate as well as zirconium concentration) on fractal-like particle structure characteristics is investigated in detail. This reveals that predominantly agglomerates (physically-bonded particles) and aggregates (chemically- or sinter-bonded particles) of nanoparticles are formed at low and high particle concentrations, respectively.