Using single-scattering albedo spectral curvature to characterize East Asian aerosol mixtures

• Published in: Journal of geophysical research. Atmospheres 2015-03, Vol.120 (5), p.2037-2052
• Main Authors: Li, Jing, Carlson, Barbara E., Lacis, Andrew A.
• Format: Article
• Language: English
• Subjects: absorbing angstrom exponent; Absorption; aerosol type; Aerosols; Air sampling; Airborne particulates; Albedo; Black carbon; Carbon; Curvature; Dust; East Asia; East Asian aerosols; Geophysics; Mathematical analysis; Optical analysis; single scattering albedo; Spectra; spectral dependence; Wavelengths
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1002/2014JD022433

Spectral dependence of aerosol single‐scattering albedo (SSA) has been used to infer aerosol composition. In particular, aerosol mixtures dominated by dust absorption will have monotonically increasing SSA with wavelength while that dominated by black carbon absorption has monotonically decreasing SSA spectra. However, by analyzing SSA measured at four wavelengths, 440, 675, 870, and 1020 nm from the Aerosol Robotic Network data set, we find that the SSA spectra over East Asia are frequently peaked at 675 nm. In these cases, we suggest that SSA spectral curvature, defined as the negative of the second derivative of SSA as a function of wavelength, can provide additional information on the composition of these aerosol mixtures. Aerosol SSA spectral curvatures for East Asia during fall and winter are considerably larger than those found in places primarily dominated by biomass burning or dust aerosols. SSA curvature is found to increase as the SSA magnitude decreases. The curvature increases with coarse mode fraction (CMF) to a CMF value of about 0.4, then slightly decreases or remains constant at larger CMF. Mie calculations further verify that the strongest SSA curvature occurs at ~40% dust fraction, with 10% scattering aerosol fraction. The nonmonotonic SSA spectral dependence is likely associated with enhanced absorption in the shortwave by dust, absorption by black carbon at longer wavelengths, and also the flattened absorption optical depth spectral dependence due to the increased particle size. Key Points SSA spectra are frequently peaked at 675 nm over East Asia The second derivative of SSA spectrum can be used to infer  fine/coarse fraction Results suggest dust fraction ~0.4 results in the largest SSA curvature