Rationale: Organic aerosols (OA) account for a large fraction of atmospheric fine particulate matter and thus are affecting climate and public health. Elucidation of the chemical composition of OA is the key for addressing the role of ambient fine particles at the atmosphere–biosphere interface and mass spectrometry is the main method to achieve this goal. Methods: High‐resolution mass spectrometry (HRMS) is on its way to becoming one of the most prominent analytical techniques, also for the analysis of atmospheric aerosols. The combination of high mass resolution and accurate mass determination allows the elemental compositions of numerous compounds to be easily elucidated. Here a new parameter for the improved classification of OA is introduced – the maximum carbonyl ratio (MCR) – which is directly derived from the molecular composition and is particularly suitable for the identification and characterization of secondary organic aerosols (SOA). Results: The concept is exemplified by the analysis of ambient OA samples from two measurement sites (Hyytiälä, Finland; Beijing, China) and of laboratory‐generated SOA based on ultrahigh‐performance liquid chromatography (UHPLC) coupled to Orbitrap MS. To interpret the results, MCR–Van Krevelen (VK) diagrams are generated for the different OA samples and the individual compounds are categorized into specific areas in the diagrams. The results show that the MCR index is a valuable parameter for representing atmospheric SOA components in composition and structure‐dependent visualization tools such as VK diagrams. Conclusions: The MCR index is suggested as a tool for a better characterization of the sources and the processing of atmospheric OA components based on HRMS data. Since the MCR contains information on the concentration of highly electrophilic organic compounds in particulate matter (PM) as well as on the concentration of organic (hydro)peroxides, the MCR could be a promising metric for identifying health‐related particulate matter parameters by HRMS.

The intensive use of pesticides in the North China Plain (NCP) has resulted in widespread contamination of pesticides in the local atmosphere, posing risks to air quality and human health. However, the occurrence and distribution of atmospheric pesticides in the NCP as well as their risk assessment have not been well investigated. In this study, 300 monthly samples were collected using passive air samplers with polyurethane foam at ten rural sites with different crop systems in Quzhou county, the NCP, from June 2021 to May 2022. The pesticides were quantified using mass-spectrometric techniques. Our results revealed that chlorpyrifos, carbendazim, and atrazine were the most frequently found pesticides in the air samples, with detection frequencies of ≥ 87 % across the samples. The average concentrations of atmospheric pesticides during spring (7.47 pg m^-3) and summer (16.05 pg m^-3) were significantly higher than those during autumn (2.04 pg m^-3) and winter (1.71 pg m^-3), attributable to the intensified application of pesticides during the warmer seasons. Additionally, cash crop sites exhibited higher concentrations (10.26 pg m^-3) of atmospheric pesticides compared to grain crop (5.59 pg m^-3) and greenhouse sites (3.81 pg m^-3), primarily due to more frequent pesticides spraying events in cash crop fields. These findings indicate a distinct spatial-temporal distribution pattern of atmospheric pesticides influenced by both seasons and crop systems. Furthermore, the model-based inhalation risk assessment indicates that inhalation exposure to atmospheric pesticides is unlikely to pose a significant public concern.

Atmospheric organic aerosol (OA) affects air quality and human health. However, compared with urban areas, the chemical composition and temporal distribution of OA in rural regions are still not well understood. In this study, one-year atmospheric particles with an aerodynamic equivalent diameter of ≤2.5 μm (PM_2.5) were collected at a rural site in Quzhou County, the North China Plain (NCP), from August 2020 to July 2021. OA in PM_2.5 samples were analyzed with an ultrahigh-performance liquid chromatograph (UHPLC) coupled to an ultrahigh-resolution Orbitrap mass spectrometer in negative mode (ESI−). The results show that the chemical composition and properties of OA varied in different seasons. According to the hierarchical cluster analysis, the molecular formulas of winter OA were close to those in spring, whereas the chemical composition of OA in summer and autumn was similar. The O/C ratio of summer OA was the highest at 1.21, followed by that in autumn (0.92) and spring (0.87), while the winter OA had the lowest O/C ratio of 0.64. It indicates that, compared to the other three seasons, OA underwent more intense oxidation processes in the summer. Moreover, winter OA contained more aromatic compounds with a relative peak abundance fraction of 40%, which may be related to anthropogenic sources (e.g., coal burning) in the winter in the NCP. In addition, biomass burning is considered an important source of OA in the rural region of Quzhou County, the NCP, in all seasons.

To improve our understanding of climate-driven long-term dynamics of eastern Asian mountain forests, we used field surveys and dendrochronological techniques to examine regeneration density, growth rate of mature trees, and growth sensitivity to climate of 3 common coniferous tree species at their respective altitudinal distribution limits on Changbai Mountain, northeastern China. The studied species were Manchurian fir (Abies nephrolepis, distributed between 780 and 1750 m asl), Korean pine (Pinus koraiensis, 780 and 1300 m asl), and Jezo spruce (Picea jezoensis var. komarovii, 1000 and 1750 m asl). Regeneration densities did not differ significantly among the elevations except for Jezo spruce, which showed a significantly lower regeneration density at 1000 m asl as compared to 1300 and 1750 m asl. All 3 species showed a significantly higher basal area increment (BAI) at the middle part of their distribution ranges than at their limits. The growth of Manchurian fir and Jezo spruce exhibited hig... Résumé: Afin d'améliorer notre compréhension de la dynamique à long terme de l'influence des facteurs climatiques sur les forêts de montagne de l'est de l'Asie, nous avons réalisé des relevés sur le terrain et utilisé des méthodes dendrochronologiques pour examiner la densité de régénération, le taux de croissance d'arbres matures et la sensibilité au climat de la croissance de trois espèces communes de conifères à leurs limites respectives de répartition altitudinale dans le massif Changbai, au nord-est de la Chine. Les espèces étudiées étaient le sapin de Mandchourie (Abies nephrolepis, retrouvé entre 780 et 1750 m asl), le pin de Corée (Pinus koraiensis, 780 à 1300 m asl) et l'épinette Jezo (Picea jezoensis, 1000 à 1750 m asl). La densité de régénération ne variait pas significativement entre les élévations, sauf pour l'épinette Jezo qui avait une densité de régénération significativement plus faible à 1000 m qu'à 1300 m et 1750 m asl. L'accroissement de la surface terrière pour les trois espèces était...