Characterization of a Three Wavelength Photoacoustic Soot Spectrometer (PASS-3) and a Photoacoustic Extinctiometer (PAX)

Abstract

Laboratory experiments were conducted for characterizing the performance of two commercially available instruments employed for the measurement of light absorption and scattering coefficients of aerosols at λ = 405, 532, and 781 nm (using three-wavelength photoacoustic soot spectrometer; PASS-3) as well as at 375 nm (using photoacoustic extinctiometer; PAX) based on photoacoustic spectroscopy and reciprocal nephelometry, respectively. The calibration factors (conversion factors from the readout to real values) associated with scattering measurements, estimated using gaseous molecules, mono-disperse polystyrene latex and ammonium sulfate particles, and/or polydisperse ammonium sulfate particles, are in good agreement with one another, typically within 5 %, 5 %, and 10 % at 375, 405, and 781 nm, respectively. In contrast, a significant particle size dependency was observed for the calibration factors at 532 nm, which is possibly because of a combination of differences in the polarization states of the lasers relative to the scattering planes and large truncation angle. Considering the estimated effective truncation angle, the typical uncertainties in calibration factors for scattering when measuring non-or weakly light-absorbing particles, with volume-based geometrical diameters of less than 700 nm, were estimated to be 12 %, 7 %, 34 %, and 17 %, at 375, 405, 532, and 781 nm, respectively. The typical uncertainties in the calibration factors for absorption measurements, which were determined using poly-disperse propane soot particles, were estimated to be 6 %, 4 %, 8 %, and 11 %, at 375, 405, 532, and 781 nm, respectively. The calibration factors for absorption determined by the poly-disperse soot particles at 375 and 405 nm were 48 % and 36 % smaller than those by light absorption of NO 2 molecules possibly because of NO 2 photolysis, although good agreement was observed at 532 nm. These results suggest that the photolysis effect should be taken into account when light absorption by NO 2 is used for calibration at 375 and 405 nm.

Light absorption of brown carbon aerosol in the PRD region of China

“…In comparison with HR-ToF-AMS, ACSM was smaller and more convenient to be transported to field sampling sites and setup in a monitoring car with limited space. The detailed description of ACSM was given by Ng et al (2011).…”

“…The calibrations of PASS-3 for flow rate, laser power, and absorption were conducted following the standard procedures provided by the operational manual, which were also applied in relevant previous studies (Arnott et al, 2000;Lan et al, 2013;Nakayama et al, 2015). Firstly, the flow rate of sample air was calibrated by a soap film flow meter, with the results shown in Table 1; secondly, the laser power for each wavelength was calibrated by a laser power meter and the error in Table 1 indicated the reading difference between the laser power meter and the laser detector inside the instrument; thirdly, the light absorption calibration was performed by measuring highly absorbing NO 2 (200 ppm) at 532 nm.…”

“…The importance of BC has been widely recognized in recent decades due to its effects of radiative forcing on climate change, while the role of BrC is far from being well known (Jacobson, 2001;Hansen et al, 1997;Haywood et al, 1997;Ramanathan and Carmichael, 2008;Gadhavi and Jayaraman, 2010;Wang et al, 2014). BrC is organic carbon which can absorb light based on a variety of chemical structures like nitrated and/or polycyclic aromatics, phenols, humic-like substances and biopolymers (Jacobson, 1999;Sun et al, 2011;Poschl, 2005). Main sources of BrC include biomass and biofuel burning, atmospheric humic-like substances (HULIS) from multiple phase actions, and photochemical oxidation of volatile organic compounds (VOCs) Bergstrom et al, 2007;Alexander et al, 2015).…”

“…at 365 and 405 nm, and contribute approximately 10 % at midvisible wavelengths, e.g. at 532 nm (Bahadur et al, 2012;Lack et al, 2012b;Washenfelder et al, 2015;Nakayama et al, 2014). During an agricultural waste burning event, BrC aerosol could contribute more than 65 % of light absorption at 370 nm and 15 % at a mid-wavelength (Favez et al, 2009).…”

Aerosol optical properties and trace gas emissions by PAX and OP-FTIR for laboratory-simulated western US wildfires during FIREX

“…The estimated uncertainty in PAX absorption and scattering measurements has been estimated as ~4-11% (Nakayama et al, 2015). …”