The Condensation Particle Counter For Rapid Atmospheric Measurements (CPC FARM): Instrument Description and Field Results

DARREN CHENG, Stavros Amanatidis, Gregory S. Lewis, Coty Jen, Carnegie Mellon University

     Abstract Number: 141
     Working Group: Instrumentation and Methods

Abstract
New particle formation (NPF) describes the process where gas molecules in the atmosphere nucleate to form a stable ~ 1 nm particle that then grow into detectable sizes. NPF influences global climate by producing 50% of the global cloud seed particles and thus altering cloud albedo and lifetimes. However, time resolution and sensitivity of current instrumentation are inadequate in measuring the reactions that produce sub-3 nm particles, the size range of freshly nucleated particles. Currently, instruments used to measure 1 – 3 nm particles include the scanning mobility particle sizer (SMPS) and the particle size magnifier (PSM). Both these instruments scan through a size distribution over minutes and therefore do not provide continuous measurements of a single particle size bin. This poor time resolution introduces uncertainty due to fluctuations in the sampled airmass and limits the identification of key processes that can result in the rapid growth of 1 – 3 nm particles. The SMPS also relies on charged particles which greatly decreases instrument sensitivity and introduces uncertainty due to extremely low and highly uncertain charging efficiencies for sub-10 nm particles. Here we present the CPC FARM as a high sensitivity and high time resolution method to measure the concentration of freshly nucleated particles. The CPC FARM consists of five water CPCs each tuned to operate at a different minimum detectable particle size. The particle size distribution is calculated using the differential measurements across the channel. The CPC FARM was deployed in Pittsburgh, PA in Fall 2023, and the measured size distribution was compared to a pair of SMPSs. Experimental results indicate that the CPC FARM can observe NPF events not captured by the SMPS which will greatly improve the calculation of NPF rates.