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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 04 Jan 2019

Research article | 04 Jan 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Light absorption property and potential source of particulate brown carbon in the Pearl River Delta region of China

Zhujie Li1,2, Haobo Tan2, Jun Zheng1, Li Liu2,3, Yiming Qin4, Nan Wang2, Fei Li2, Yongjie Li5, Mingfu Cai3, Yan Ma1, and Chak K. Chan4 Zhujie Li et al.
  • 1School of Environmental Science and Engineering, Nanjing University of Information Science and Technology, Nanjing, China
  • 2Key Laboratory of Regional Numerical Weather Prediction, Institute of Tropical and Marine Meteorology, China Meteorological Administration, Guangzhou, China
  • 3Department of Atmospheric Science, Sun yat-sen University, Guangzhou, China
  • 4School of Energy and Environment, City University of Hong Kong, Hong Kong, China
  • 5Department of Civil and Environmental Engineering, Faculty of Science and Technology, University of Macau, Macau, China

Abstract. Brown carbon (BrC) is a type of light-absorbing component of organic aerosol (OA), covering from near-ultraviolet (UV) to visible wavelength ranges, and thus may cause additional aerosol radiative effect in the atmosphere. While high concentrations of OA have been observed in the Pearl River Delta (PRD) region of China, optical properties and the corresponding radiative forcing of BrC in PRD are still not well understood. In this work, we conducted a set of comprehensive measurements of atmospheric particulate matters from 29 November 2014 to 5 January 2015 to investigate aerosol composition, optical properties, source origins and radiative forcing effects at a suburban station of Guangzhou. Particle absorption Ångström exponent (AAE) was deduced and utilized to differentiate light absorption by BrC from black carbon (BC). The results showed that the average absorption contributions of BrC were 25.9±9.0% at 370nm, 19.7±7.9% at 470nm, 14.1±6.9% at 520nm, 11.6±5.6% at 590nm and 7.7±4.4% at 660nm, respectively. A sensitivity analysis of the evaluation of absorption Ångström exponent of BC (AAEBC) was conducted based on the Mie theory calculation, assuming that the BC-containing aerosol was internally mixed, with a core-shell configuration. The corresponding uncertainty of BrC absorption contribution was acquired. We found that variations in the imaginary refractive index (RI) of BC core can significantly affect the estimation of BrC absorption contribution. However, BrC absorption contribution was relatively less sensitive to the real part of RI of BC core and was least sensitive to the real part of RI of non-light absorbing shell. BrC absorption was closely related to aerosol potassium cation content (K+), a common tracer of biomass burning emission, which was most likely associated with straw burning in the rural area of western PRD. Diurnal variation of BrC absorption revealed that primary organic aerosol had a larger BrC absorption capacity than secondary organic aerosol (SOA) had. Radiative transfer simulations showed that BrC absorption may cause 2.2±2.3Wm−2 radiative forcing at the top of atmosphere (TOA) and contribute 14.2±6.2% of the aerosol warming effect. A chart was constructed to conveniently assess the BrC radiative forcing efficiency in the studied area with reference to a certain aerosol single-scattering albedo (SSA) and BrC absorption contribution at various wavelengths. Evidently, BrC radiative forcing efficiency was higher in shorter wavelength.

Zhujie Li et al.
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Short summary
BrC may significantly affect aerosol radiative forcing and the magnitude of which is typically deduced from BC absorption measurements, assuming a unit AAE of BC. Here, we estimated the error associated this AAE segregation method for various configurations of BC core and coating materials. We also evaluated the BrC contribution to the aerosol radiative forcing in the PRD region and a table was constructed to easily assess BrC radiative forcing efficiency for various aerosol optical properties.
BrC may significantly affect aerosol radiative forcing and the magnitude of which is typically...