Broadband spectrum characteristics and radiative effects of primary brown carbon from wood pyrolysis

Qianqian Liu; Xuezhe Xu; Weixiong Zhao; Jiacheng Zhou; Md Masudur Rahman; Yuanqing Cai; Shuo Wang; Bo Fang; Weijun Zhang

doi:10.1016/j.scitotenv.2023.163500

Broadband spectrum characteristics and radiative effects of primary brown carbon from wood pyrolysis

Sci Total Environ. 2023 Jul 15:882:163500. doi: 10.1016/j.scitotenv.2023.163500. Epub 2023 Apr 18.

Authors

Qianqian Liu¹, Xuezhe Xu², Weixiong Zhao³, Jiacheng Zhou², Md Masudur Rahman⁴, Yuanqing Cai², Shuo Wang², Bo Fang², Weijun Zhang⁵

Affiliations

¹ School of Environmental Science and Optoelectronic Technology, University of Science and Technology of China, Hefei 230026, Anhui, China; Laboratory of Atmospheric Physico-Chemistry, Anhui Institute of Optics and Fine Mechanics, HFIPS, Chinese Academy of Sciences, Hefei 230031, Anhui, China.
² Laboratory of Atmospheric Physico-Chemistry, Anhui Institute of Optics and Fine Mechanics, HFIPS, Chinese Academy of Sciences, Hefei 230031, Anhui, China.
³ School of Environmental Science and Optoelectronic Technology, University of Science and Technology of China, Hefei 230026, Anhui, China; Laboratory of Atmospheric Physico-Chemistry, Anhui Institute of Optics and Fine Mechanics, HFIPS, Chinese Academy of Sciences, Hefei 230031, Anhui, China. Electronic address: wxzhao@aiofm.ac.cn.
⁴ Laboratory of Atmospheric Physico-Chemistry, Anhui Institute of Optics and Fine Mechanics, HFIPS, Chinese Academy of Sciences, Hefei 230031, Anhui, China; Department of Electrical and Electronic Engineering, Pabna University of Science and Technology, Pabna 6600, Bangladesh.
⁵ School of Environmental Science and Optoelectronic Technology, University of Science and Technology of China, Hefei 230026, Anhui, China; Laboratory of Atmospheric Physico-Chemistry, Anhui Institute of Optics and Fine Mechanics, HFIPS, Chinese Academy of Sciences, Hefei 230031, Anhui, China. Electronic address: wjzhang@aiofm.ac.cn.

PMID: 37076010
DOI: 10.1016/j.scitotenv.2023.163500

Abstract

Brown carbon (BrC), known as light-absorbing organic aerosol in the near-ultraviolet (UV) and short visible region, plays a significant role in the global and regional climate change. A detailed understanding of the spectral optical properties of BrC is beneficial for reducing the uncertainty in radiative forcing calculation. In this work, the spectral properties of primary BrC were investigated by using a four-wavelength broadband cavity-enhanced albedometer with central wavelengths at 365, 405, 532 and 660 nm. The BrC samples were generated by the pyrolysis of three types of wood. During the pyrolysis process, the measured average single scattering albedo (SSA) at 365 nm was about 0.66 to 0.86, where the average absorption Ångström exponent (AAE) was between 5.8 and 7.8, and the average extinction Ångström exponent (EAE) was within 2.1 to 3.5. The full spectral measurement of SSA (300-700 nm) was realized by an optical retrieval method and the retrieved SSA spectrum was directly applied to evaluate aerosol direct radiative forcing (DRF) efficiency. The DRF efficiency over ground of various primary BrC emissions increased from 5.3 % to 68 % as compared to the non-absorbing organic aerosol assumption. A decrease of about 35 % in SSA would cause the DRF efficiency over ground to change from cooling effect to warming effect (from -0.33 W/m² to +0.15 W/m²) in the near-UV band (365-405 nm). The DRF efficiency over ground of strongly absorptive primary BrC (lower SSA) contributed 66 % more than weakly absorptive primary BrC (higher SSA). These findings proved the importance of broadband spectral properties of BrC, which are substantial for radiative forcing evaluation of BrC and should be considered in global climate models.

Keywords: Brown carbon (BrC); Radiative forcing; Single scattering albedo; Spectral properties; Wood pyrolysis.