Application of an O-ring pinch device as a constant pressure inlet (CPI) for airborne sampling

Abstract

We present a novel and compact design of a constant pressure inlet (CPI) developed for use in airborne aerosol mass 10 spectrometry. In particular the inlet system is optimized for aerodynamic lenses commonly used in aerosol mass spectrometers, where efficient focusing of aerosol particles into a vacuum chamber requires a precisely controlled lens pressure, typically of a few hPa. The CPI device can also be used in gas phase sampling instruments in a large range of altitude and inlet pressure. The constant pressure is achieved by changing the inner diameter of a properly scaled O-ring that acts as a critical orifice. The CPI control keeps air pressure and thereby mass flow rate (≈0.1 l/min) upstream of an aerodynamic lens constant, deviating at most 15 by only ±2 % from a pre-set value. In our setup a pressure sensor downstream of the O-ring controls the pinch mechanism via a feedback loop and setpoint conditions are reached within seconds. The device was implemented in a few instruments, which were successfully operated on different research aircraft covering a wide range of ambient pressures, from sea level up to about 55 hPa. Details of operation and quality of aerosol particle transmission are evaluated by laboratory experiments and in-flight data with a single particle mass spectrometer.

Design, characterization, and first field deployment of a novel aircraft-based aerosol mass spectrometer combining the laser ablation and flash vaporization techniques

“…1. During aircraft operation the sample air flow is provided by a constant pressure inlet (Molleker et al, 2020) serving as a critical orifice at the instrument's front end. The particles are focused in the aerodynamic lens (ADL) into a narrow beam and accelerated into the vacuum chamber, where they 15 first reach the optical particle detection units (PDU1 and PDU2 in Fig.…”

“…If is not maintained constant, the transmission of the particles through the inlet into the vacuum system becomes altitude dependent (Zhang et al, 2002). For this purpose, a newly developed, automatically-controlled compressible rubber O-ring setup is deployed (Molleker et al, 2020). As ADL we integrated the intermediate pressure lens IPL-013 (Peck et al, 2016;Xu et al, 2017) to focus the particles into a beam with sufficiently small 15 divergence, i.e., less than the diameter of the vaporizer element at a distance of 55 cm downstream of the exit of the ADL.…”

Supplementary material to "Design, characterization, and first field deployment of a novel aircraft-based aerosol mass spectrometer combining the laser ablation and flash vaporization techniques"

“…The measurements with the OPC were conducted only with PDU1 to reduce measurement time and were adopted from Molleker et al (2020). During these measurements, the thresholds at PMT1 were adjusted (increasing with particle size) to filter the particle signal from signals caused by residual particle fragments in the PSL suspension.…”

“…The parameter can be used as an approximation to describe the ADL transmission efficiency as used by Molleker et al (2020) for the ERICA. The data of the gray curve ( ) was provided by the manufacturer (Aerodyne Inc.) in the datasheet of the here applied ADL model (IPL-013).…”

Chemical composition and source attribution of submicron aerosol particles in the summertime Arctic lower troposphere

“…The instrument has been described before in detail (Brands et al, 2011;Roth et al, 2016;Schmidt et al, 2017;Köllner et al, 2017) and is only briefly reviewed here. Particles enter the system through a critical orifice (for details see Molleker et al, 2020). The following Liu-type aerodynamic lens focuses particles into a narrow beam (Liu et al, 1995a(Liu et al, , b, 2007.…”