A novel way to calculate shortwave black carbon direct radiative effect

Wei Chen; Zhe Wang; Haimeng Zhao; Kai Qin

doi:10.1016/j.scitotenv.2020.142961

A novel way to calculate shortwave black carbon direct radiative effect

Sci Total Environ. 2021 Feb 20:756:142961. doi: 10.1016/j.scitotenv.2020.142961. Epub 2020 Oct 14.

Authors

Wei Chen¹, Zhe Wang², Haimeng Zhao³, Kai Qin⁴

Affiliations

¹ College of Geoscience and Surveying Engineering, China University of Mining & Technology, Beijing 100083, China. Electronic address: chenw@cumtb.edu.cn.
² College of Geoscience and Surveying Engineering, China University of Mining & Technology, Beijing 100083, China.
³ Guangxi Colleges and Universities Key Laboratory of Unmanned Aerial Vehicle (UAV) Remote Sensing, Guilin University of Aerospace Technology, Guilin 541004, China.
⁴ School of Environmental Science and Spatial Informatics, China University of Mining and Technology, Xuzhou 221116, China.

PMID: 33109365
DOI: 10.1016/j.scitotenv.2020.142961

Abstract

Black carbon (BC) aerosol has a strong radiative forcing effect and significantly affects human beings and the environment. Therefore, it is important to quantitatively calculate its direct radiative effect (BC DRE) at the surface (SFC) and the top of the atmosphere (TOA). Current studies mainly use empirical formula methods or broadband methods to calculate BC DRE. However, these two methods do not consider the differences of sky diffuse light ratios in different wavelength bands. To overcome this problem, a new scheme named the multiband synthetic method is proposed to calculate blue sky albedo at MODIS narrow bands, and then, the blue sky albedo at the whole shortwave band is synthesized with these separate narrowband blue sky albedos. Based on BC concentration measured in Xuzhou over two years (from May 2014 to July 2016), aerosol optical depth (AOD) and microphysical parameters provided by AERONET, and the black sky albedo (BSA) and white sky albedo (WSA) provided by Google Earth Engine (GEE) products, shortwave BC DRE was calculated numerically with the use of the 6S radiative transfer model. The range of BC DRE computed by the multiband synthetic method at the TOA and SFC are 0.84 ± 0.08 to 3.27 ± 1.01W/m² and -14.57 ± 4.53 to -4.31 ± 0.36W/m². The shortwave BC DRE calculated by the multiband synthetic method was higher than that calculated with the broadband method and empirical formula method by 0.11% to 0.36% (at the SFC), 0.14% to 1.4% (at the SFC) and 3.4% to 10.1% (at the TOA), 5.5% to 15.8% (at the TOA), respectively. The BC DREs calculated by these three methods have small differences at the SFC. However, the difference was large at the TOA. The results of this study suggest that it is important to consider the differences between different narrow bands when calculating the broadband shortwave blue sky albedo.

Keywords: Black carbon; Blue sky albedo; Multiband synthetic method; Shortwave direct radiative effect.