Measuring the Detection Efficiency of Neutral Flame-Formed Materials by Two-Component Fluid-Water Condensation Particle Counters (Fluid-WCPCs)
Farnaz Khosravi, Gregory S. Lewis, FRANCESCO CARBONE, University of Connecticut
Abstract Number: 393
Working Group: Instrumentation and Methods
Abstract
Atmospheric nucleation is a key process in new particle formation, with significant implications for climate, air quality, and human health. While ion-induced nucleation has been extensively studied, neutral aerosols smaller than 10 nm remain poorly characterized. A principal challenge lies in the difficulty of detecting and quantifying these particles experimentally, as they cannot be manipulated by electric fields. Consequently, advanced aerosol diagnostic instruments, such as Condensation Particle Counters (CPCs), are required to accurately determine their number concentration. Although CPCs can detect both neutral and charged particles, their detection efficiency must be carefully evaluated under application-specific conditions. However, the literature has yet to introduce a well-established and reliable procedure for calibrating CPC detection efficiency for uncharged aerosols. This study proposes a new approach to address this gap by quantifying the size-dependent detection efficiency of neutral sub-5 nm flame-formed carbonaceous aerosols using the two-component fluid-water CPCs resulting from coupling a WCPC prototype (model ADI-2021-1, Aerosol Dynamics Inc.) to a saturator inlet operated with either Diethylene Glycol (DEG), n-Butanol (nBA), Isopropanol (IPA), or Ethanol (EtOH). Results demonstrate that the DEG-WCPC, the nBA-WCP, the IPA-WCPC, and the EtOH-WCPC enable the detection of uncharged flame-formed carbonaceous aerosols at least as small as 2.5nm with relatively high sizing resolutions. The comparison with published results quantifying the detection efficiency of the naturally charged fraction of the same flame-formed carbonaceous aerosols highlights that the lack of an electric charge causes a moderate enlargement of the d50% size of aerosols detected with 50% efficiency. The increase in the d50% size is observed to be relatively smaller for the EtOH-WCPC and the DEG-WCPC than for the nBA -WCPC, the IPA-WCP.