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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.

Submitted as: research article 04 Nov 2019

Submitted as: research article | 04 Nov 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).

Amplification of black carbon light absorption induced by atmospheric aging: temporal variation at seasonal and diel scales in urban Guangzhou

Jia Yin Sun1,2, Cheng Wu1,2, Dui Wu1,2,3, Chunlei Cheng1,2, Mei Li1,2, Lei Li1,2, Tao Deng3, Jian Zhen Yu4,5,6, Yong Jie Li7, Qiani Zhou1,2, Yue Liang1,2, Tianlin Sun1,2, Lang Song1,2, Peng Cheng1,2, Wenda Yang1,2, Yanxiang Cen11, Zhen Zhou1,2, Chenglei Pei8,9,10, Yanning Chen10, and Huiqing Nian11 Jia Yin Sun et al.
  • 1Institute of Mass Spectrometry 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, CMA, Guangzhou 510080, China
  • 4Department of Chemistry, Hong Kong University of Science & Technology, Hong Kong, China
  • 5Division of Environment & Sustainability, Hong Kong University of Science & Technology, Hong Kong, China
  • 6Atmospheric Research Center, HKUST Fok Ying Tung Research Institute, Guangzhou 511400, China
  • 7Faculty of Science and Technology, University of Macau, China
  • 8State Key Laboratory of Organic Geochemistry and Guangdong Key Laboratory of Environmental Protection and Resources Utilization, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
  • 9University of Chinese Academy of Sciences, Beijing 100049, China
  • 10Guangzhou Environmental Monitoring Center, Guangzhou 510030, China
  • 11Guangzhou Hexin Analytical Instrument Limited Company, Guangzhou 510530, China

Abstract. Black carbon (BC) is an important climate forcer in the atmosphere. Amplification of light absorption can occur by coatings on BC aerosols, an effect that remains one of the major sources of uncertainties for accessing the radiative forcing of BC. In this study, the absorption enhancement factor (Eabs) was quantified by the minimum R squared (MRS) method using elemental carbon (EC) as the tracer. Two field campaigns were conducted in urban Guangzhou at the Jinan university super site during both wet season (July 31–September 10, 2017) and dry season (November 15, 2017–January 15, 2018) to explore the temporal dynamics of BC optical properties. The average concentration of EC was 1.94 ± 0.93 and 2.81 ± 2.01 μgC m−3 in the wet and dry seasons, respectively. Mass absorption efficiency at 520 nm by primary aerosols (MAEp520) determined by MRS exhibit a strong seasonality (8.6 m2g−1 in the wet season and 16.8 m2g−1 in the dry season). Eabs520 was higher in the wet season (1.51 ± 0.50) and lower in the dry season (1.29 ± 0.28). Absorption Ångström exponent (AAE470-660) in the dry season (1.46 ± 0.12) were higher than that in the wet season (1.37 ± 0.10). Collective evidence showed that the active biomass burning (BB) in dry season effectively altered optical properties of BC, leading to elevated MAE, MAEp and AAE in dry season comparing to those in wet season. Diurnal Eabs520 was positively correlated with AAE470-660 (R2 = 0.71) and negatively correlated with the AE33 aerosol loading compensation parameter (k) (R2 = 0.74) in the wet season, but these correlations were significantly weaker in the dry season, which may be related to the impact of BB. This result suggests that lensing effect was dominating the AAE diurnal variability during the wet season. The effect of secondary processing on Eabs diurnal dynamic were also investigated. The Eabs520 exhibit a clear dependency on secondary organic carbon to organic carbon ratio (SOC/OC). Eabs520 correlated well with nitrate, implying that gas-particle partitioning of semi-volatile compounds may potentially play an important role in steering the diurnal fluctuation of Eabs520. In dry season, the diurnal variability of Eabs520 was associated with photochemical aging as evidenced by the good correlation (R2 = 0.69) between oxidant concentrations (Ox=O3+NO2) and Eabs520.

Jia Yin Sun et al.
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Jia Yin Sun et al.
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Short summary
Atmospheric aging processes can lead to Black carbon (BC) light absorption enhancement (Eabs). The temporal variability of BC Eabs remained poorly characterized. This study investigated the temporal variations of BC Eabs at both seasonal and diel scales in an urban environment. Factors affecting the temporal variability of BC Eabs were also analyzed, including variability in emission sources and various types of atmospheric aging processes.
Atmospheric aging processes can lead to Black carbon (BC) light absorption enhancement (Eabs)....