Aerosol optical absorption and spectral dependence measurement with photoacoustic spectroscopy

Light-absorbing carbonaceous aerosols mainly generated from the combustion of biomass and fossil fuels, play an important role in the global environment ^[1]. Multi-wavelength in-situ measurement of carbonaceous aerosol optical absorption is important both for reduce errors in assessing radiative forcing and component identification or source appointment of aerosols (such as biomass burning and diesel soot) with absorption Ångström exponent (AAE) ^[2]. A differential photoacoustic spectrometer (PAS) using a 438 nm laser diode was developed for simultaneously measure the aerosol optical absorption coefficient and the concentration of NO₂. In order to evaluate the reliability of the differential photoacoustic spectrometer, we compared the NO₂ concentration measured by PAS with the data from environmental monitoring station and showed good consistency. In the actual atmospheric measurement process, we observed a good correlation between the light absorption characteristics of aerosols and the concentration of NO₂ within a certain time range. In addition, a novel multi-wavelength photoacoustic spectrometer (MW-PAS) was developed to measure the aerosol optical absorption coefficients and its wavelength-dependent characteristics in the UV-VIS-NIR bands (405, 638, 808 nm). The performance of MW-PAS was evaluated by measuring the light absorption characteristics of kerosene soot aerosol. The measurement results are agreed with the results reported in literatures ^[3].

 

Reference

[1] J.G. Radney, R. You, M.R. Zachariah, C.D. Zangmeister, Direct in-situ mass specific absorption spectra of biomass burning particles generated from smoldering hard and softwoods. Environ. Sci. Technol. 51, 5622-5629 (2017)

[2] T. Ajtai, N. Utry, M. Pintér, B. Major, G. Szabó, A method for segregating the optical absorption properties and the mass concentration of winter time urban aerosol. Atmos. Environ.122, 313-320 (2015)

[3] M. Gyawali, W.P. Arnott, R.A. Zaveri, C. Song, H. Moosmüller, L. Liu, M.I. Mishchenko, L.-W.A. Chen, M.C. Green, J.G. Watson, and J.C. Chow, Photoacoustic optical properties at UV, VIS, and near IR wavelengths for laboratory generated and winter time ambient urban aerosols. Atmos. Chem. Phys. 12, 2587-2601 (2012)