Molecular Characterization of Water‐Soluble Brown Carbon Chromophores in Beijing, China

Abstract

High abundance and strong light absorption of atmospheric brown carbon (BrC) have been reported in East Asia, especially in northern China. However, the molecular‐level understanding of BrC chromophores in this area is still limited and quite challenging. In this study, elemental composition of individual BrC chromophores was first investigated in the megacity of Beijing, China, using a powerful platform for the characterization of BrC chromophores, with combination of high‐performance liquid chromatography coupled to a UV/Vis absorbance detector and a time‐of‐flight mass spectrometer with an electrospray ionization source. The results from this study showed that S‐containing compounds (e.g., CHOS and CHONS) significantly increased in highly polluted days compared to lightly polluted days, probably due to increased emissions from sources such as coal combustion and favorable conditions for organosulfates formation. It was found that CHON and CHO compounds were the most abundant water‐soluble organic compounds in Beijing especially during the wintertime. Nitroaromatic compounds were the major water‐soluble BrC chromophores, with three major BrC chromophores (e.g., C6H5NO3, C7H7NO4, and C6H5NO4) found under all conditions, while other specific BrC chromophores with CHON‐ and CHO‐containing elemental formulas identified and varied in different seasons and pollution conditions. Overall, the water‐soluble BrC chromophores identified in this study explained about 2%–18% of the bulk BrC absorbance over the wavelength range of 300–400 nm. In‐depth studies on exploring more BrC chromophores as well as their chemical structures, related sources, and formation mechanisms should be conducted in the future.

The Roles of N, S, and O in Molecular Absorption Features of Brown Carbon in PM2.5 in a Typical Semi‐Arid Megacity in Northwestern China

“…These results are similar to those reported in Beijing by Yan et al. (2020), which found major BrC contributors accounted for 19%, 8%, 4%, and 2%, respectively, of total absorption and the corresponding absorbance were 29.5, 12.4, 6.2, and 3.1 Mm −1 , respectively. N‐containing molecules were dominant among the top BrC throughout the sampling periods, and only limited contributions from the other molecule types, which provides an insight that the other thousands of molecules were less light‐absorptive and had minor contributions to BrC.…”

Chemical Fingerprinting of HULIS in Particulate Matters Emitted from Residential Coal and Biomass Combustion

“…Light absorption by HULIS strongly depends on their chromophores, whose known species include N-containing aromatic compounds, , polycyclic aromatic hydrocarbons and their derivatives, , lignin-derived products, , distillation products, and phenols . Several classes and subclasses of chromophores were identified and are detailed in Table S4.…”

Secondary Formation of Aerosols Under Typical High‐Humidity Conditions in Wintertime Sichuan Basin, China: A Contrast to the North China Plain

“…A total of 96% of the identified CHOS formulas and 54% of the identified CHONS formulas could exist as OSs and nitrooxy‐OSs. An increase in OS formation during haze episode in Beijing was also observed in previous studies (Qiu et al., 2020; Xie et al., 2020; Yan et al., 2020). Here, we cannot completely exclude the possibility of CHOS being hydroxysulfonates or CHONS being nitro‐OSs due to the lack of MS‐MS analysis.…”