The characteristics of brown carbon aerosol during winter in Beijing. (February 2016)

• Record Type: Journal Article
• Authors: Cheng, Yuan; He, Ke-bin; Du, Zhen-yu; Engling, Guenter; Liu, Jiu-meng; Ma, Yong-liang; Zheng, Mei; Weber, Rodney J.
• Is Part Of: Atmospheric environment. Volume 127(2016)
• Page Start: 355
• Page End: 364
• Publication Date: 2016-02
• Subjects: Brown carbon -- Light absorption -- WSOC -- Methanol extract -- Biomass burning; Air -- Pollution -- Periodicals; Air -- Pollution -- Meteorological aspects -- Periodicals; 551.51
• DOI: 10.1016/j.atmosenv.2015.12.035
• Languages: English
• ISSNs: 1352-2310

Abstract

Abstract: Brown carbon (i.e., light-absorbing organic carbon, or BrC) exerts important effects on the environment and on climate in particular. Based on spectrophotometric absorption measurements on extracts of bulk aerosol samples, this study investigated the characteristics of BrC during winter in Beijing, China. Organic compounds extractable by methanol contributed approximately 85% to the organic carbon (OC) mass. Light absorption by the methanol extracts exhibited a strong wavelength dependence, with an average absorption Ångström exponent of 7.10 (fitted between 310 and 450 nm). Normalizing the absorption coefficient ( b abs ) measured at 365 nm to the extractable OC mass yielded an average mass absorption efficiency (MAE) of 1.45 m 2 /g for the methanol extracts. This study suggests that light absorption by BrC could be comparable with black carbon in the spectral range of near-ultraviolet light. Our results also indicate that BrC absorption and thus BrC radiative forcing could be largely underestimated when using water-soluble organic carbon (WSOC) as a surrogate for BrC. Compared to previous work relying only on WSOC, this study provides a more comprehensive understanding of BrC aerosol based on methanol extraction. Highlights: The majority (∼85%) of the OC mass in Beijing aerosol can be extracted by methanol. A larger portion of brown carbon (BrC) absorption comes from OC insoluble in water. OC extractable by methanol provides a better estimation of BrC compared to WSOC. BrC absorption could be comparable with BC in the spectral range of UV light. Anthropogenic BrC tends to be more light-absorbing than biogenic BrC.