Airborne and laboratory studies of an IAGOS instrumentation package containing a modified CAPS particle extinction monitor

Abstract

An evaluation of the operation and performance of a Cavity Attenuated Phase-Shift Particle Extinction Monitor (CAPS PM ex ) was performed for use on board commercial aircraft as part of the research infrastructure IAGOS (In-service Aircraft for a Global Observing System, www.iagos.org). After extensive laboratory testing, a new flow system, using mass flow controllers, was installed to maintain constant purge and sample flows under low and varying pressure conditions. The instrument was then tested for pressures as low as 200 hPa and evaluated against particle-free compressed air and CO 2 . Extinction coefficients for the studied gases were in close agreement with literature values with differences between 2.2% and 8%, proving that the CAPS technology works at low pressures. The instrument's limit of detection, with respect to 3 times the variability of the background signal for the full pressure range, was 0.2 Mm ¡1 for 60s integration time. During its first research aircraft operations, the IAGOS instrument prototype, composed of one CAPS PMex and one OPC, showed excellent results regarding the stability of the instruments and the potential for characterizing different aerosol types and for estimating the contribution of sub-and super-mm sized particles to aerosol light extinction.

Airborne survey of trace gases and aerosols over the Southern Baltic Sea: from clean marine boundary layer to shipping corridor effect

“…During the BALTIC'15 campaign we deployed the airborne version of the CAPS, which was specifically developed for the IAGOS package and validated by de Faria et al (2017).…”

“…Aerosol number concentrations and particle number size distributions were calculated on 10 seconds intervals from the UHSAS and OPC measurements in the 100-1000 nm and in the 1000-2500 nm diameter ranges, respectively. According to the instruments' calibration, a refractive index of 1.59, (polystyrene latex standard material), was used for the Mie calculations (de Faria et al, 2017). From here forward, the scattering coefficient estimated for N Acc is called r spAcc , while for the N Crs is named r spCrs .…”

Laboratory Validation and Field Deployment of a Compact Single-Scattering Albedo (SSA) Monitor

“…The CAPS PM ssa (Onasch et al, 2015), uses the same principle to measure light extinction as the CAPS PM ex , but it also contains, located at the centre of the measurement cell, a 10 cm diameter integrating sphere capable of measuring light scattering on the same aerosol sample, as shown in Figure 2. The integrating sphere acts as an integrating nephelometer, which measures the scattering of light by particles at all angles, only excluding the near 0 and near 180° 130 angles since at these directions the opening of the extinction chamber is located, allowing the sample and light beam to pass through.…”

“…A novel instrument based on cavity attenuated phase-shift technology and incorporating an integrating sphere was 55 recently developed by Aerodyne Research, Inc. This novel instrument represents a major step forward in the observation of aerosol optical properties since it simultaneously measures two of the three aerosol optical parameters from the same air sample, reducing the potential sources of sampling biases (Onasch et al, 2015). The two main applications of the CAPS PM ssa instrument, apart from the direct measurement of scattering and extinction coefficients, are the indirect measurement of the aerosol absorption coefficient and the measurement of the single-scattering albedo.…”

The influence of the baseline drift on the resulting extinction values of a CAPS PMex

“…A detailed description of the Instrument is given by Massoli et al (2010). CAPS PMex has already been compared and characterized in combination with other instruments (Petzold et al, 2013) and used in various campaigns (Yu et al, 2013;Perim de Faria et al, 2017).…”