Determination of the aerosol particle size distribution by means of the diffusion battery: Analytical inversion

<p>The algorithm of the analytical inversion of aerosol size distribution is proposed in this work. As the diffusion battery separates particles into several fractions according to their diffusivity, the total spectrum can be represented as the sum of spectra of fractions. Analytical formulas are derived to calculate mean diameters for particles in different fractions using diffusion battery penetrations as input parameters. The spectra of fractions are approximated by lognormal functions. Two analytical solutions for the aerosol size distribution inversion problem are discussed. The sizing accuracy of analytical solutions is investigated, comparing them with the measurements through transmission electron microscopy using the laboratory-generated NaCl aerosol. The agreement is demonstrated to be within 10% accuracy. It is shown that in case of two-mode size distribution, the spectrum components are well resolved for rather distant peaks (modal diameters of 10 and 300 nm) and poorly resolved for nearby modes (50 and 300 nm). To improve the peak resolution, the procedure of spectrum correction is applied demonstrating an excellent peak separation. Finally, the peak resolution is experimentally verified for the laboratory-generated two-mode spectra of tungsten oxide–NaCl aerosol with the modal diameters of 10 and 60 nm, respectively. Both analytical solutions demonstrated good peak resolution.</p> <p>Copyright © 2018 American Association for Aerosol Research</p

Aerosol diffusion battery: The retrieval of particle size distribution with the help of analytical formulas

<p>A new algorithm is proposed for the determination of aerosol particle size distribution from a set of screen diffusion battery penetrations. The idea is to determine the size spectra of the fractions of particles separated by the sections of diffusion battery, so the total size distribution is the sum of the spectra of fractions. The spectrum of each fraction is approximated by the lognormal function, which is defined by two parameters: the standard geometric deviation (SGD) and geometric mean diameter. The SGD value is chosen to be 1.35 for each fraction. The geometric mean diameters of fractions are calculated from the diffusion battery penetrations. For this purpose, analytical formulas are derived to link the mean single-fiber collection efficiency for each fraction with the experimentally measured penetrations. Then the mean diameters of fractions are calculated from the collection efficiencies using the fan model filtration theory. To achieve a better size resolution, numerical approach is proposed to calculate the particle size spectrum using the analytical solution as an initial approximation. The validity of the analytical and numerical solutions is investigated by comparing them with the spectra determined by means of transmission electron microscopy and gravity settling. For this purpose, the aerosol is generated using the evaporation-nucleation technique, Collison-type nebulizer, and hot-wire bulb generator. It is found that the analytical solution demonstrates a good sizing accuracy but relatively poor size resolution, while the numerical approach results in both good sizing accuracy and good size resolution for the two-mode aerosol.</p> <p>Copyright © 2018 American Association for Aerosol Research</p