A Compact Aerosol Mobility Imager for Instantaneous Aerosol Size Distribution Measurements
JIAOSHI ZHANG, Jing Li, Xiaoyu Chen, Steven Spielman, Susanne Hering, Jian Wang, Washington University in St. Louis
Abstract Number: 482
Working Group: Instrumentation and Methods
Abstract
Aerosol Mobility Imager (AMI), a compact instrument for rapid measurements of aerosol size distribution, is presented. AMI employs a parallel plate mobility separator wherein the electric field strength varies along the width of the plate. Under the influence of the electric field, charged particles are spatially separated inside the separator according to their electrical mobility. An extraction growth cell (EGC) then extracts a portion of the flow carrying the spatially separated particles and converges the extracted flow into a narrow focusing nozzle slit, while simultaneously growing the particles by water condensation. Grown particles exiting the focusing slit are imaged to capture both the number and mobility dependent position of the particles, which allows for derivation of aerosol size distribution. The employment of the new EGC greatly reduces the instrument size, weight, and power consumption compared to the previously developed Fast Integrated Mobility Spectrometer (FIMS) (Wang et al., 2017a; Wang et al., 2017b). The combination of a compact size and fast measurement speed makes AMI an ideal instrument for deployments in many laboratory studies and field observations, including onboard platforms such as the unmanned aerial vehicle and tethered balloon system. Here, we present the numerical simulations and experimental characterizations of the newly developed AMI. The particle trajectories and growth of spatially separated particles inside AMI were simulated and the AMI transfer function, mobility resolution, and transmission efficiency were derived based on the simulated particle trajectories. A prototype AMI was constructed, and the simulated AMI performances including mobility sizing accuracy, detection efficiency, and transfer functions were validated experimentally using DMA-classified aerosols. The results demonstrate that AMI is capable of rapid and accurate aerosol size distribution measurement, while maintaining a sufficient mobility resolution for measurements of ambient aerosols.