Combined analyses of hygroscopic properties of organic and inorganic components of three representative black carbon samples recovered from pyrolysis

Minli Wang; Yiqun Chen; Heyun Fu; Xiaolei Qu; Guofeng Shen; Bengang Li; Dongqiang Zhu

doi:10.1016/j.scitotenv.2021.145393

Combined analyses of hygroscopic properties of organic and inorganic components of three representative black carbon samples recovered from pyrolysis

Sci Total Environ. 2021 Jun 1:771:145393. doi: 10.1016/j.scitotenv.2021.145393. Epub 2021 Jan 27.

Authors

Minli Wang¹, Yiqun Chen¹, Heyun Fu¹, Xiaolei Qu¹, Guofeng Shen², Bengang Li², Dongqiang Zhu³

Affiliations

¹ State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Jiangsu 210046, China.
² School of Urban and Environmental Sciences, Key Laboratory of the Ministry of Education for Earth Surface Processes, Peking University, Beijing 100871, China.
³ State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Jiangsu 210046, China; School of Urban and Environmental Sciences, Key Laboratory of the Ministry of Education for Earth Surface Processes, Peking University, Beijing 100871, China. Electronic address: zhud@pku.edu.cn.

PMID: 33545465
DOI: 10.1016/j.scitotenv.2021.145393

Abstract

Hygroscopicity of black carbon (BC) aerosols is a key factor determining their climate forcing effect and atmospheric lifetime. However, the compositional dependence of BC hygroscopicity is not well understood. Here, a variety of different compositional components were separated from three representative BC samples recovered from pyrolysis (grass and wheat straw derived BC, household soot), including water extracted fraction of BC (WEBC, 9-21 wt%), residue fraction of BC after water extraction (R-WEBC, 79-91 wt%), water extracted minerals (WEM, 9-18 wt%), alkali extracted organic carbon (OC_AE, 1-9 wt%), and elemental carbon (EC, 37-48 wt%). The bulk BC and separated BC components were analyzed in detail by elemental analysis and combined spectroscopic analyses. Their equilibrium hygroscopicity was measured by gravimetric method over a range of relative humidity (RH) levels (10-94%). Compared with the two organic components (OC_AE and EC), the inorganic component (WEM) exhibited much stronger water uptake at all RH levels. At 94% RH level, WEM accounted for 16-139% of the overall water uptake by BC, whereas OC_AE and EC accounted for only 1-3% and 6-26%, respectively. The XRD analysis of WEBC and WEM from household soot at varying RH levels indicated that the enhanced water uptake by these two components as well as that by bulk BC at high RH levels was due to the deliquescent salts (e.g., KCl, NH₄Cl, KNO₃, and NaCl). The strong hysteresis loops observed for bulk BC and WEBC could be attributed to the organic-facilitated drastic structural and morphological rearrangement of mineral particles as evidenced by the optical microscope analysis. The diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis reaffirmed the dominant role played by the inorganic component in the hygroscopic behaviors of BC.

Keywords: Black carbon; Deliquescence; Hygroscopicity; Hysteresis; Inorganic component; Organic component.