Spectral dependency of aerosol light-absorption over the East China sea region

We studied the spectral dependencies of aerosol light-absorption over the East China Sea region using sky radiometer data collected at Cape Hedo (26.87°N, 128.25°E), Okinawa, Japan from 2006 to 2008. Absorption Angstrom Exponent (AAE) was around 1 for most of the observation data, indicating black carbon (BC) as the dominant light-absorbing aerosol. However, high values of AAE were often found in the spring season. Aerosols with such high AAE were characterized by comparatively high optical thickness (τ), low single scattering albedo (ω), and an increase of ω with wavelength (λ). Additionally, dust aerosols were considerably high when such high AAEs were observed. Such high AAEs could not be explained by considering only BC and dust as absorbing aerosols, but could be well explained by including the role of brown carbon aerosols. This finding highlights a complex scenario of light-absorbing aerosols in the spring season in this region, and suggests the necessity of considering the role of such brown carbon aerosols on a light-absorption phenomenon for adequately understanding aerosol climatology. The study also discussed that AAE of dust aerosol should be used with care with the known size distribution and spectral values of the imaginary refractive index.