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

Abstract

Abstract. Air pollution by particulate matter in China affects human health, the ecosystem and the climate. However, the chemical composition of particulate aerosol, especially of the organic fraction, is still not well understood. In this study, particulate aerosol samples with a diameter of ≤2.5 µm (PM2.5) were collected in January 2014 in three cities located in northeast, east and southeast China, namely Changchun, Shanghai and Guangzhou. Organic aerosol (OA) in the PM2.5 samples was analyzed by an ultrahigh-performance liquid chromatograph (UHPLC) coupled to a high-resolution Orbitrap mass spectrometer in both negative mode (ESI-) and positive mode electrospray ionization (ESI+). After non-target screening including the assignment of molecular formulas, the compounds were classified into five groups based on their elemental composition, i.e., CHO, CHON, CHN, CHOS and CHONS. The CHO, CHON and CHN groups present the dominant signal abundances of 81 %–99.7 % in the mass spectra and the majority of these compounds were assigned to mono- and polyaromatics, suggesting that anthropogenic emissions are a major source of urban OA in all three cities. However, the chemical characteristics of these compounds varied between the different cities. The degree of aromaticity and the number of polyaromatic compounds were substantially higher in samples from Changchun, which could be attributed to the large emissions from residential heating (i.e., coal combustion) during wintertime in northeast China. Moreover, the ESI- analysis showed higher H/C and O/C ratios for organic compounds in Shanghai and Guangzhou compared to samples from Changchun, indicating that OA undergoes more intense photochemical oxidation processes in lower-latitude regions of China and/or is affected to a larger degree by biogenic sources. The majority of sulfur-containing compounds (CHOS and CHONS) in all cities were assigned to aliphatic compounds with low degrees of unsaturation and aromaticity. Here again, samples from Shanghai and Guangzhou show a greater chemical similarity but differ largely from those from Changchun. It should be noted that the conclusions drawn in this study are mainly based on comparison of molecular formulas weighted by peak abundance and thus are associated with inherent uncertainties due to different ionization efficiencies for different organic species.

Molecular Characteristics of Organosulfur Compounds in Guangzhou, South China: Heterogeneous Secondary Reactions Drivers the Molecular Distribution

“…'brien et al, 2014;Willoughby et al, 2014;Jiang et al, 2016;Jiang et al, 2020), clouds (Zhao et al, 2013;Bianco et al, 2018) and rainwater (Altieri et al, 2009) collected in the different places of the world measured by negative ESI-FT-ICR MS, indicating that the OrgSs are enriched with saturated structures (Table S3). However, the O/C ratios of OrgSs presented in this work are slightly higher than those of cloud water (Bianco et al, 2018;Zhao et al, 2013), and comparable to the values measured in east-middle Chinese cities, (Wang et al, 2016;Wang et al, 2017a) while are remarkably less-oxidized than samples of organic aerosols measured in Mainz and Chinese cities measured using high-resolution obtrip MS on pollution days (Wang et al, 2019;Wang et al, 2021b). Note that the average DBE value of CHOS2 compounds is approximately 3 times that of CHOS1 compounds, indicating that CHOS2 probably contains numerous aromatic OSs, but CHOS1 compounds are dominated by OSs with long aliphatic carbon chains and low degrees of oxidation and unsaturation.…”

Factors Influencing the Molecular Compositions and Distributions of Atmospheric Nitrogen‐Containing Compounds

“…The CHON+ and CHON-compounds were located in areas that corresponded to oxidized unsaturated compounds and intermediately oxidized organic compounds, respectively. The mean H/C and O/C ratios of the CHON+ and CHON-compounds were close to or slightly greater than the mean H/C and O/C ratios of the regional and rural sites of the Pearl River Delta (Jiang et al, 2020;Lin et al, 2012), as well as the mean H/C and O/C ratios of ambient aerosol samples collected in biomass burning potentially influenced sites and large cities such as Beijing (Jiang et al, 2016;Wang et al, 2018), Shanghai (Wang, Hayeck, et al, 2017), Changchun, and Mainz (Wang et al, 2018(Wang et al, , 2021. However, the mean H/C and O/C ratios were significantly less than the mean H/C and O/C ratios of urban aged atmospheric aerosols collected from Cambridge, UK; California, USA.…”

“…However, the mean H/C and O/C ratios were significantly less than the mean H/C and O/C ratios of urban aged atmospheric aerosols collected from Cambridge, UK; California, USA. (O'Brien et al, 2014;Rincón et al, 2012;Willoughby et al, 2014); and Guangzhou on hazy days (Wang et al, 2021), as well as the aged atmospheric media of cloud water (Bianco et al, 2018;Zhao et al, 2013) and rainwater (Altieri et al, 2012). Furthermore, the degrees of oxidation and saturation of CHON compounds in Guangzhou were close to the degrees of oxidation and saturation of the BBOA samples (Cai et al, 2020;Song et al, 2018;Tang et al, 2020), vehicle emission, and tunnel aerosols (Tang et al, 2020), but significantly greater than the degrees of oxidation and saturation of fine particles from coal combustion (Song et al, 2018(Song et al, , 2019Tang et al, 2020) and off-road engine emissions (Cui et al, 2019).…”

Evolution of organic carbon during COVID-19 lockdown period: Possible contribution of nocturnal chemistry

“…Over the past few decades, the poor air quality in China has attracted intensive attentions ( Fan et al, 2021 ; Liu et al, 2020a ; Wang et al, 2021b ; Zong et al, 2021 ). To improve air quality, the Chinese government has implemented a series of strict emission control strategies, such as the Air Pollution Prevention and Control Action Plan in 2013 ( Cai et al, 2017 ; Ge et al, 2021 ).…”