Radical Formation by Fine Particulate Matter Associated with Highly Oxygenated Molecules

Abstract

Highly oxygenated molecules (HOMs) play an important role in the formation and evolution of secondary organic aerosols (SOA). However, the abundance of HOMs in different environments and their relation to the oxidative potential of fine particulate matter (PM) are largely unknown. Here, we investigated the relative HOM abundance and radical yield of laboratory-generated SOA and fine PM in ambient air ranging from remote forest areas to highly polluted megacities. By electron paramagnetic resonance and mass spectrometric investigations, we found that the relative abundance of HOMs especially the dimer and low volatile types in ambient fine PM was positively correlated with the formation of radicals in aqueous PM extracts. SOA from photooxidation of isoprene, ozonolysis of α-and βpinene as well as fine PM from tropical (central Amazon) and boreal (Hyytiälä, Finland) forests exhibited a higher HOM abundance and radical yield than SOA from photooxidation of naphthalene and fine PM from urban sites (Beijing, Guangzhou, Mainz, Shanghai, and Xi'an), confirming that HOMs are important constituents of biogenic SOA to generate radicals. Our study provides new insights into the chemical relationship of HOM abundance, composition, and sources with the yield of radicals by laboratory and ambient aerosols, enabling better quantification of component-specific contribution of source-or sitespecific fine PM to its climate and health effects. ASSOCIATED CONTENT Supporting Information Supporting material consists of three tables and four figures.

Urban organic aerosol composition in eastern China differs from north to south: molecular insight from a liquid chromatography–mass spectrometry (Orbitrap) study

“…On the contrary, the aromaticity equivalent X C for organics detected in Changchun-, X C (Changchun-) = 2.13, is higher than that for Shanghai-, X C (Shanghai-) = 1.92, and Guangzhou-, X C (Guangzhou-) = 1.65. Furthermore, the relative peak abundance fraction of compounds with O/C ≥ 0.6, which are considered to be highly oxidized compounds (Tu et al, 2016), is 31 % in Changchun-, and higher in Shanghai-(46 %) and Guangzhou-(51 %). These observations indicate that urban OA in northeast China features a lower degree of oxidation and a higher degree of aromaticity compared to urban OA in east and southeast China.…”

“…Recently, ultrahigh-resolution mass spectrometry (UHRMS), such as Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and the Orbitrap MS, coupled with soft ionization sources (e.g., electrospray ionization, ESI, and atmospheric pressure chemical ionization, APCI), has been introduced to elucidate the molecular composition of OA (Nizkorodov et al, 2011;Lin et al, 2012a, b;Rincón et al, 2012;Noziere et al, 2015;Kourtchev et al, 2016;Tong et al, 2016;Tu et al, 2016;Brüggemann et al, 2017Brüggemann et al, , 2019Wang et al, 2017Wang et al, , 2018Wang et al, , 2019aFleming et al, 2018;Laskin et al, 2018;Song et al, 2018;Daellenbach et al, 2019;Ning et al, 2019). Due to the two outstanding features of high resolving power and high mass accuracy, UHRMS can give precise elemental compositions of individual organic compounds.…”

Atmospheric conditions and composition that influence PM<sub>2.5</sub> oxidative potential in Beijing, China

“…Although PAHs are not redox-active (Charrier and Anastasio, 2012), they are precursors to redox-active oxy-PAHs (quinones) and nitro-PAHs (Atkinson and Arey, 2007) and have well-established intrinsic cellular toxicity (reviewed in Moorthy et al, 2015), mediated by their conversion to hydroxy-PAHs, which exert mutagenic and teratogenic effects and also induce transcriptional modifications and oxidative stress. EC and n-alkanes are also non-redox-active, and the exact mechanisms of their toxicities are unclear (Levy et al, 2012); however, SOA derived from the interaction of n-alkanes with NO x with photooxidation (Lim and Ziemann, 2005;Presto et al, 2010) is likely both to contribute to the redox activity of samples (Tuet et al, 2017) and to have more toxic properties than its precursors (Xu et al, 2020b). The sample from 22 November 2016 has a particularly high concentration of cooking markers (palmitic acid, stearic acid and cholesterol).…”

Characterization and comparison of PM<sub>2.5</sub> oxidative potential assessed by two acellular assays

“…Oxidative stress arises when the presence and production of ROS overwhelms the antioxidant's defenses, and can lead to cell and tissue damage and D. Gao et al: Characterization and comparison of PM 2.5 induction of chronic and degenerative diseases (Das, 2016;Halliwell, 1994;Pizzino et al, 2017). The ability of PM to generate ROS in vivo, referred to as the oxidative potential (OP) of particles, has gained increasing attention as a possibly more integrative health-relevant measure of ambient PM toxicity than PM mass concentration, which may contain a mix of highly toxic (e.g., polycyclic aromatic hydrocarbons (PAHs), quinones, environmentally persistent free radicals, highly oxygenated organic molecules, and transition metals) to relatively benign (e.g., sulfate and ammonium nitrate) PM components (Frampton et al, 1999;Khachatryan et al, 2011;Lippmann, 2014;Tong et al, 2018Tong et al, , 2019.…”