Polycyclic Aromatic Carbon: A Key Fraction Determining the Light Absorption Properties of Methanol-Soluble Brown Carbon of Open Biomass Burning Aerosols

Abstract

The composition and radiative forcing of light-absorbing brown carbon (BrC) aerosol remain poorly understood. Polycyclic aromatics (PAs) are BrC chromophores with fused benzene rings. Understanding the occurrence and significance of PAs in BrC is challenging due to a lack of standards for many PAs. In this study, we quantified polycyclic aromatic carbon (PAC), defined as the carbon of fused benzene rings, based on molecular markers (benzene polycarboxylic acids, BPCAs). Open biomass burning aerosols (OBBAs) of 22 rainforest plants were successively extracted with water and methanol for the analysis of water- and methanol-soluble PAC (WPAC and MPAC, respectively). PAC is an important fraction of water- and methanol-soluble organic carbon (WSOC and MSOC, respectively). WPAC/WSOC ranged from 0.03 to 0.18, and MPAC/MSOC was even higher (range: 0.16–0.80). The priority polycyclic aromatic hydrocarbons contributed less than 1% of MPAC. The mass absorption efficiency (MAE) of MSOC showed a strong linear correlation with MPAC/MSOC (r = 0.60–0.95, p < 0.01). The absorption Ångström exponent (AAE) of methanol-soluble BrC showed a strong linear correlation with the degree of aromatic condensation of MPAC, which was described by the average number of carboxylic groups of BPCA (r = −0.79, p < 0.01). This result suggested that PAC was a key fraction determining the light absorption properties (i.e., light absorptivity and wavelength dependence) of methanol-soluble BrC in OBBAs.

Effects of Nitrate Radical Levels and Pre-Existing Particles on Secondary Brown Carbon Formation from Nighttime Oxidation of Furan

“…73,74 Nitrophthalic acid, the hydrolysis product of nitrophthalic anhydrides, was also identified as a chromophore in the aerosols produced by the combustion of biomass. 75 Since both of these hydrolysis products are organic markers of SOA, 76−79 the hydrolysis of anhydrides can be used to track the formation and evolution of secondary BrC. Overall, our findings highlight the influence of NO 3 levels and pre-existing particles on the chemical composition and optical properties of nighttime furan SOA, whereas bulk and molecular characterizations of SOA constituents and chromophores are necessary for better experimental constraint and a more complete process-level understanding of their formation.…”

“…Even under wet conditions where anhydrides could be hydrolyzed, the resulting products may still be chromophores. For example, phthalic acid (or 1,2-benzenedicarboxylic acid), the hydrolysis product of phthalic anhydride, has been reported as one of the most prevalent BrC chromophores in ambient observations. , Nitrophthalic acid, the hydrolysis product of nitrophthalic anhydrides, was also identified as a chromophore in the aerosols produced by the combustion of biomass . Since both of these hydrolysis products are organic markers of SOA, − the hydrolysis of anhydrides can be used to track the formation and evolution of secondary BrC.…”

Continuous Measurement and Molecular Compositions of Atmospheric Water‐Soluble Brown Carbon in the Nearshore Marine Boundary Layer of Northern China: Secondary Formation and Influencing Factors

“…Several studies have revealed that some components of BrC include nitro‐aromatics, polycyclic aromatic hydrocarbon (PAHs), polyphenols, and sulfur‐containing compounds (Bluvshtein et al., 2017; Budisulistiorini et al., 2017; Fleming et al., 2018; R. J. Huang et al., 2018; Lin et al., 2016; Y. Sun et al., 2021; Yuan et al., 2021). Numerous observation and laboratory studies have shown that secondary BrC could be formed from anthropogenic and biogenic precursors via multiphase chemistry under various conditions, and those formation processes have been partially revealed through laboratory simulations (Aiona, Lee, Leslie, et al., 2017; Aiona, Lee, Lin, et al., 2017; Kampf et al., 2016; Lambe et al., 2013; C. Li, He, Fang, et al., 2020; Siemens et al., 2022; Y. Wang, Mekic, et al., 2021; J. Xu et al., 2018).…”

“…Several studies have revealed that some components of BrC include nitro-aromatics, polycyclic aromatic hydrocarbon (PAHs), polyphenols, and sulfur-containing compounds (Bluvshtein et al, 2017;Budisulistiorini et al, 2017;Fleming et al, 2018; R. J. Lin et al, 2016;Y. Sun et al, 2021;Yuan et al, 2021).…”

Molecular-Scale Investigation on the Formation of Brown Carbon Aerosol via Iron-Phenolic Compound Reactions in the Dark

“…On the other hand, the chemical composition of secondary BrC produced by the Fe-PC reactions is mysterious, making it difficult to evaluate its effect on haze formation as well as its potential health hazards. The application of ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) provides an opportunity to enhance our understanding of atmospheric OA at the molecular level. − It has been used to investigate the molecular diversity of OA fractions collected from various atmospheric samples ,, and to elucidate the relationships between the optical properties of OA and their molecular compositions. , However, no research has tried to reveal the molecular characteristics of phenols derived from secondary BrC using FT-ICR MS, and how different phenolic precursors affect the molecular composition of secondary BrC remains unclear. In addition, no attempt has been made to compare laboratory-generated BrC with real OA at the molecular level.…”