Chemical Characteristics of Organic Aerosols in Shanghai: A Study by Ultrahigh‐Performance Liquid Chromatography Coupled With Orbitrap Mass Spectrometry

Abstract

Particulate matter 2.5 (PM2.5) filter samples were collected in July and October 2014 and January and April 2015 in urban Shanghai and analyzed using ultrahigh‐performance liquid chromatography coupled to Orbitrap mass spectrometry. The measured chromatogram‐mass spectra were processed by a nontarget screening approach to identify significant signals. In total, 810–1,510 chemical formulas of organic compounds in the negative polarity (negative electrospray ionization (ESI−)) and 860–1,790 in the positive polarity (ESI+), respectively, were determined. The chemical characteristics of organic aerosols (OAs) in Shanghai varied among different months and between daytime and nighttime. In the January samples, organics were generally richer in terms of both number and abundance, whereas those in the July samples were far lower. More CHO− (compounds containing only carbon, hydrogen, and oxygen and detected in ESI−) and CHOS− (sulfur‐containing organics) were found in the daytime samples, suggesting a photochemical source, whereas CHONS− (nitrogen‐ and sulfur‐containing organics) were more abundant in the nighttime samples, due to nocturnal nitrate radical chemistry. A significant number of monocyclic and polycyclic aromatic compounds, and nitrogen‐ and sulfur‐containing heterocyclic compounds, were detected in all samples, indicating that biomass burning and fossil fuel combustion made important contributions to the OAs in urban Shanghai. Additionally, precursor‐product pair analysis indicates that the epoxide pathway is an important formation route for organosulfates observed in Shanghai. Moreover, a similar analysis suggests that 35–57% of nitrogen‐containing compounds detected in ESI+ could be formed through reactions between ammonia and carbonyls. Our study presents a comprehensive overview of OAs in urban Shanghai, which helps to understand their characteristics and sources.

Quantification of known and unknown terpenoid organosulfates in PM10 using untargeted LC–HRMS/MS: contrasting summertime rural Germany and the North China Plain

“…The remaining peaks from the triplicate measurements were combined to give average peak areas for each compound in each sample. Lastly, the elemental ratios, ring double bond equivalents (RDBE) and aromaticity equivalents Xc (Wang et al 2017a;Yassine et al 2014) of the assigned MFs were calculated.…”

“…Furthermore, the molecular weight of OSs is larger than that for the corresponding carboxylic acid because of the large molecular weight contribution from sulfate, which eventually also increases the total PM mass. Moreover, the suppressed formation of carboxylic acids in the presence of large amounts of particulate sulfate and NO x might have important implications for past and future source apportionment studies, since such MT oxidation products have previously been used extensively as tracer compounds for biogenic SOA Wang et al 2017a;Yttri et al 2011). Thus, such studies might have underestimated the biogenic contributions to the total PM concentrations.…”

“…So far, only a few studies on SOA components have attempted to combine the advantages of state-of-the-art HRMS, such as Orbitrap MS, with classical liquid separation techniques (Vogel et al 2016;Wang et al 2018aWang et al , 2017aWang et al , 2016. One of the main reasons for the rather low number of such studies is probably the tedious and non-routine analysis of large amounts of data acquired from LC-HRMS measurements.…”

Molecular Characterization of Organosulfates in Highly Polluted Atmosphere Using Ultra‐High‐Resolution Mass Spectrometry

“…The obtained chromatogram‐MS data were processed with a MZmine‐2.30 software (http://mzmine.github.io) to obtain the m/z ratios, formulas, retention times, and peak areas of detected organic compounds (Hu et al, 2016; Wang, Hayeck, et al, 2017). The molecular formula assignment was mainly based on detected m/z values with a mass tolerance of ±2 ppm.…”

Organic aerosol source apportionment in Zurich using an extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF-MS) – Part 2: Biomass burning influences in winter

“…The chemical analysis of an aerosol online proton-transfer-reaction mass spectrometer (CHARON-PTR-MS) has no significant thermal decomposition but the ionization scheme fragments typical SOA molecules (Eichler et al, 2015;Muller et al, 2017). Several semicontinuous methods have also been developed, including thermal desorption aerosol GC (TAG-MS, GC family; Williams et al, 2006) and a gas and aerosol chemical-ionization time-offlight mass spectrometer (FIGAERO-CIMS; Lopez-Hilfiker et al, 2014). However, these systems remain subject to some degree of thermal decomposition, as well as potential reaction on the collection substrate, and significantly lower time resolution.…”