Atmospheric brown carbon in China haze is dominated by secondary formation

Xiaodi Liu; Can Wu; Zheng Li; Rongjie Li; Fanglin Wang; Shaojun Lv; Rui Li; Fan Zhang; Haoyang Wang; Chenlong Liang; Lei Zhang; Gehui Wang

doi:10.1016/j.scitotenv.2024.173901

Atmospheric brown carbon in China haze is dominated by secondary formation

Sci Total Environ. 2024 Oct 1:945:173901. doi: 10.1016/j.scitotenv.2024.173901. Epub 2024 Jun 14.

Authors

Xiaodi Liu¹, Can Wu¹, Zheng Li¹, Rongjie Li¹, Fanglin Wang¹, Shaojun Lv¹, Rui Li¹, Fan Zhang¹, Haoyang Wang², Chenlong Liang², Lei Zhang³, Gehui Wang⁴

Affiliations

¹ Key Laboratory of Geographic Information Science of the Ministry of Education, School of Geographic Sciences, East China Normal University, Shanghai 200241, China.
² Laboratory of Mass Spectrometry Analysis, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, China.
³ China Academy of Meteorological Sciences, Beijing, China.
⁴ Key Laboratory of Geographic Information Science of the Ministry of Education, School of Geographic Sciences, East China Normal University, Shanghai 200241, China. Electronic address: ghwang@geo.ecnu.edu.cn.

PMID: 38880143
DOI: 10.1016/j.scitotenv.2024.173901

Abstract

Brown carbon (BrC) is a class of light-absorbing organic aerosols (OA) and has significant influence on atmospheric radiative forcing. However, the current limited understanding of the physicochemical properties of BrC restricts the accurate evaluation of its environmental effects. Here the optical characteristics and chemical composition of BrC during wintertime in the Yangtze River Delta (YRD) region, China were measured by using high-resolution aerosol mass spectrometry (HR-AMS) and UV-vis spectrometry. Our results showed that BrC in PM_2.5 during the campaign was dominated by water-soluble organics, which consist of less oxidized oxygenated OA (LO-OOA), more oxidized oxygenated OA (MO-OOA), fossil fuel OA (FFOA) and biomass burning OA (BBOA). MO-OOA and BBOA were the strongest light absorbing BrC at 365 nm (Abs₃₆₅), followed by LO-OOA and FFOA with a mass absorption coefficient (MAC) being 0.74 ± 0.04, 0.73 ± 0.03, 0.48 ± 0.04 and 0.39 ± 0.06 m² g^-1 during the campaign, respectively. In the low relative humidity (RH < 80 %) haze periods Abs₃₆₅ of LO-OOA contributed to 44 % of the total light absorption at 365 nm, followed by MO-OOA (31 %), FFOA (21 %) and BBOA (4 %). In contrast, in the high-RH (RH > 80 %) haze periods Abs₃₆₅ was dominated by MO-OOA, which accounted for 62 % of the total Abs₃₆₅, followed by LO-OOA (17 %), BBOA (13 %) and FFOA (8 %). Chemical composition analysis further showed that LO-OOA and MO-OOA are produced from gas-phase photooxidation of VOCs and aerosol aqueous reactions, respectively, in which ammonia significantly enhanced the formation and light absorption of BrC in the high RH haze period. On average, >75 % of the total Abs_365nm in the YRD region during the haze events was contributed by LO-OOA and MO-OOA, suggesting that atmospheric BrC in China haze periods is predominantly formed by secondary reactions.

Keywords: Aerosol aqueous-phase reaction; Brown carbon; Gas-phase photooxidation; Light absorption; Water-soluble organics.