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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 1 | Copyright
Atmos. Chem. Phys., 18, 289-309, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 11 Jan 2018

Research article | 11 Jan 2018

Quantifying black carbon light absorption enhancement with a novel statistical approach

Cheng Wu1,2, Dui Wu1,2,3, and Jian Zhen Yu4,5,6 Cheng Wu et al.
  • 1Institute of Mass Spectrometer and Atmospheric Environment, Jinan University, Guangzhou 510632, China
  • 2Guangdong Provincial Engineering Research Center for On-line Source Apportionment System of Air Pollution, Guangzhou 510632, China
  • 3Institute of Tropical and Marine Meteorology, China Meteorological Administration, Guangzhou 510080, China
  • 4Division of Environment, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
  • 5Atmospheric Research Centre, Fok Ying Tung Graduate School, Hong Kong University of Science and Technology, Nansha, China
  • 6Department of Chemistry, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China

Abstract. Black carbon (BC) particles in the atmosphere can absorb more light when coated by non-absorbing or weakly absorbing materials during atmospheric aging, due to the lensing effect. In this study, the light absorption enhancement factor, Eabs, was quantified using a 1-year measurement of mass absorption efficiency (MAE) in the Pearl River Delta region (PRD). A new approach for calculating primary MAE (MAEp), the key for Eabs estimation, is demonstrated using the minimum R squared (MRS) method, exploring the inherent source independency between BC and its coating materials. A unique feature of Eabs estimation with the MRS approach is its insensitivity to systematic biases in elemental carbon (EC) and σabs measurements. The annual average Eabs550 is found to be 1.50±0.48 (±1 SD) in the PRD region, exhibiting a clear seasonal pattern with higher values in summer and lower in winter. Elevated Eabs in the summertime is likely associated with aged air masses, predominantly of marine origin, along with long-range transport of biomass-burning-influenced air masses from Southeast Asia. Core–shell Mie simulations along with measured Eabs and absorption Ångström exponent (AAE) constraints suggest that in the PRD, the coating materials are unlikely to be dominated by brown carbon and the coating thickness is higher in the rainy season than in the dry season.

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Short summary
This work presents a new approach, minimum R squared (MRS) method, to quantify black carbon aerosols light absorption enhancement factor, Eabs, from ambient measurements using an Aethalometer and field carbon analyzer. Application of MRS on 1 year of measurement is demonstrated. This study provides a potential alternative to explore the Eabs information using inexpensive instrumentation with wider temporal coverage.
This work presents a new approach, minimum R squared (MRS) method, to quantify black carbon...