Counting and sizing of polydisperse airborne nanoparticles have attracted most attentions owing to increasing widespread presence of airborne engineered nanoparticles or ultrafine particles. Here we report a miniature aerosol sensor to detect particle size distribution of polydisperse ultrafine particles based on ion diffusion charging and electrical detection. The aerosol sensor comprises a couple of planar electrodes printed on two circuit boards assembled in parallel, where charging, precipitation and measurement sections are integrated into one chip, which can detect aerosol particle size in of 30–500 nm, number concentration in range of 5 × 10² – 5 × 10⁷ /cm³. The average relative errors of the measured aerosol number concentration and the particle size are estimated to be 12.2% and 13.5% respectively. A novel measurement scheme is proposed to actualize a real-time detection of polydisperse particles by successively modulating the measurement voltage and deducing the particle size distribution through a smart data fusion algorithm. The effectiveness of the aerosol sensor is experimentally demonstrated via measurements of polystyrene latex (PSL) aerosol and nucleic acid aerosol, as well as sodium chloride aerosol particles.

It is necessary to recognize the spatial distribution of ion density and temperature in some practical applications. While numerical modeling is a useful method to fulfill this task, a self-consistent numerical model based on the first few moments of the Boltzmann transport equation coupled to Poisson's equation was built using COMSOL Multiphysics to simulate the dc discharge of a needle-to-plane geometry in atmospheric pressure. Simulation of the discharge was carried out for an actual geometry in aerosol sensors when only the main compositions of air and the main collisional populating and depopulating processes were considered. The simulation results demonstrated that the space occupied by the positive ions with a density of sufficiently charging aerosol particles was very limited. In the meanwhile, the electron temperature in the vicinity of the entire plane electrode was higher than the melting point of most metals. Experiments of measuring the current inducted by charged particles with a diameter of 95 nm using devices with narrowed channels showed that the specific current increased to nearly five times when the width of the channel in the charging stage decreases from 5 to 2 mm. Furthermore, the ablation of the plane electrode used in the experiments occurred on almost the entire surface, which was agreed with the prediction by simulation.