Development of a cavity-enhanced aerosol albedometer

Abstract

Abstract. We report on the development of a cavityenhanced aerosol single-scattering albedometer based on incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) combined with an integrating sphere (IS) for simultaneous in situ measurements of aerosol scattering and extinction coefficients in an exact same sample volume. The cavity-enhanced albedometer employed a blue light-emitting-diode (LED)-based IBBCEAS approach for the measurement of wavelength-resolved aerosol optical extinction over the spectral range of 445-480 nm and an integrating sphere nephelometer coupled to the IBBCEAS setup for the measurement of aerosol scattering. The scattering signal was measured with a single-channel photomultiplier tube (PMT), providing an averaged value over a narrow bandwidth (full-width at half-maximum, FWHM, ∼ 9 nm) in the spectral region of 465-474 nm. A scattering coefficient at a wavelength of 470 nm was deduced as an averaged scattering value over the spectral region of 465-474 nm and used for data analysis and instrumental performance comparison. Performance evaluation of the albedometer was carried out using laboratory-generated particles and ambient aerosol. The scattering and extinction measurements of monodisperse polystyrene latex (PSL) spheres generated in the laboratory proved excellent correlation between two channels of the albedometer. The retrieved refractive index (RI) of the PSL particles from the measured scattering and extinction efficiencies agreed well with the values reported in previously published papers. Aerosol light scattering and extinction coefficients, single-scattering albedo (SSA) and NO 2 concentrations in an ambient sample were directly and simultaneously measured using the albedometer developed. The instrument developed was validated via an intercomparison of the measured aerosol scattering coefficients and NO 2 trace gas concentrations to a TSI 3563 integrating nephelometer and a chemiluminescence detector, respectively.

Single Scattering Albedo Monitor for Airborne Particulates

“…Thompson and co-workers took a similar approach but replaced the cosine-corrected detector with a nephelometer employing an integrating sphere (Dial et al 2010), the concept of which was previously described in Varma et al (2003) and Abu-Rahmah et al (2006). And most recently, Zhao et al (2014) have employed incoherent broadband cavity-enhanced spectroscopy (IBBCEAS) and an integrating sphere to directly measure the SSA of ambient aerosol. A somewhat different approach has been developed by Sharma et al (2013 and references therein) who coupled a photoacoustic spectrometer and nephelometer to measure absorption and scattering, respectively.…”

“…Thus, in order to measure total particle extinction under ambient conditions, the atmospheric scientist had little choice but to obtain separate absorption and scattering measurements as measuring extinction requires extremely long pathlengths (see Zhao et al 2014). However, with the development of optical loss techniques such as cavity ring-down (CRD) (Moosm€ uller et al 2005;Baynard et al 2007) and cavity attenuated phase shift (CAPS) ; , the user community now has ready access to accurate and precise direct extinction measurements as well.…”

Aerosol optical properties measurements by a CAPS single scattering albedo monitor: Comparisons between summer and winter in Beijing, China

“…The Cavity Ring‐Down systems (CRD) and Cavity Attenuated Phase Shift (CAPS) monitors have been widely used to measure b ext directly [ Massoli et al ., ; Strawa et al ., ], yet the simultaneous measurements of b ext and b sp are relatively new [ Onasch et al ., ; Zhao et al ., ]. Onasch et al .…”

Portable broadband cavity-enhanced spectrometer utilizing Kalman filtering: application to real-time, in situ monitoring of glyoxal and nitrogen dioxide

“…6. An intercomparison of NO 2 measurements against alternative methods is not part of this study, but we note that our earlier broadband spectroscopy instruments have performed very well compared to commercial chemiluminescence detectors (Thermo 42i NOx analyzer) [24,28].…”

“…Compared to DOAS, which has a very long physical pathlength through the atmosphere, BBCES achieves comparable or superior sensitivity in a compact and robust system that is suited to mobile, high spatial resolution observations [17]. BBCES is also widely used for the measurement of other trace gases and atmospheric aerosol extinction [25][26][27][28], and references therein].…”