Improved Ultrafine Aerosol Sizing with NMASS Pulse Height Analysis (NMASS-PHA)

MATTHEW BROWN, Steven Cevaer, Luke Ziemba, NASA

     Abstract Number: 225
     Working Group: Instrumentation and Methods

Abstract
Nucleation-mode aerosol plays a significant role in the climate cycle, including stratospheric chemistry cycles and cloud lifetimes. One major source of nucleation-mode aerosols in the stratosphere was found to be from aircraft exhaust (Williamson, 2021). Current Nucleation-mode size distributions are performed with the Nucleation-Mode Aerosol Sizing Spectrometer (NMASS; Brock, 2000). The NMASS consists of a series of particle counters that activate the aerosols to droplets at 5 different cut sizes to measure particle size distributions at 1 Hz in the ultrafine particle size range, however with a poor sizing resolution of only 4 bins. Despite losing the information of most of the initial particle size distribution when activated to droplets, Pulse Height Analysis (PHA) can be used to resolve droplet sizing corresponding to the activating particle size near the cut point due to the supersaturation gradient and thus duration of droplets in supersaturation. For a single counter, sizing around the cut size provides little value; however, with 5 logarithmically-spaced sizing channels in the NMASS, the PHA can fill in the gaps between the relatively coarse bins. We designed new electronics in the NMASS for Pulse Height Analysis (NMASS-PHA), including photodiode and data acquisition (DAQ) circuits, and developed processing algorithms for sizing and stitching consecutive particle counters. The additional sizing resolution results in no cost to weight or power.