**Abstract:** A research team led by Professor Jiang Jingkun from the School of Environment at Tsinghua University has made significant advancements in the field of atmospheric online high-resolution mass spectrometry monitoring. The study focuses on the molecular and seasonal characteristics of organic compounds in urban Beijing, particularly volatile organic compounds (VOCs) and their oxidation products, including primary and multi-stage oxidation products. The research, published in two prestigious journals, "Atmospheric Chemistry and Physics" and "Environmental Science & Technology," utilized advanced chemical ionization high-resolution mass spectrometry techniques to conduct long-term observations in Beijing's urban atmospheric environment. The team employed a Vocus Proton-Transfer-Reaction Time-of-Flight Mass Spectrometer (Vocus-PTR-TOF) to measure organic precursors and their primary oxidation products. This instrument, with its enhanced sensitivity and mass resolution, was able to detect and analyze a broader range of species compared to traditional proton transfer mass spectrometers. Within the mass range of m/z 50-200, the researchers identified 512 organic molecules, 44% of which were at sub-parts per trillion (ppt) levels, and 38% contained 3-8 oxygen atoms. These newly identified oxygenated molecules are predominantly medium/semi-volatile organic compounds, many of which are primary oxidation products of anthropogenic sources like benzene and toluene, and biogenic sources like monoterpenes and terpenes. These compounds play a crucial role in the concentration of atmospheric oxygenated organic molecules, hydroxyl radical reactivity, and the formation of secondary organic aerosols (SOAs). For the higher oxidation state oxygenated organic molecules (OOMs), the team developed an online chemical ionization Orbitrap mass spectrometer (CI-Orbitrap) using nitrate ions and their clusters as reagent ions. This instrument enabled the long-term measurement of OOMs in Beijing's urban atmosphere. In the mass range of m/z 200-600, the researchers identified 2403 OOMs, providing insights into the clear homologous and oxygenation characteristics of these molecules. These findings reflect the rich and complex oxidation processes occurring in the atmosphere. Through precursor tracing analysis, it was determined that the OOMs in Beijing are primarily derived from the oxidation of anthropogenic precursors such as aromatic hydrocarbons and aliphatic compounds. Additionally, the study identified OOM dimers related to new particle formation and important intermediates like organic radicals, which have been rarely reported in previous urban atmospheric studies due to limitations in measurement technology. The research, titled "Molecular and Seasonal Characteristics of Organic Vapors in Urban Beijing: Insights from Vocus-PTR Measurements" and "Resolving Atmospheric Oxygenated Organic Molecules in Urban Beijing Using Online Ultrahigh-Resolution Chemical Ionization Mass Spectrometry," highlights the seasonal variations in the concentration and composition of these organic molecules. The findings contribute to a deeper understanding of the formation and evolution processes of atmospheric organic molecules, which are critical for managing air pollution and improving air quality in urban environments. The lead authors of the papers are Dr. An Zhaojin, a recent Ph.D. graduate from the School of Environment now working as a postdoctoral researcher at Harvard University, and Yuan Yi, a Ph.D. student at Tsinghua University since 2020. Professor Jiang Jingkun served as the corresponding author for both studies. The research was a collaborative effort involving institutions such as Beijing University of Chemical Technology, Fudan University, Wuhan University, Nanjing University, Dalian University of Technology, Henan Normal University, University of Helsinki, Harvard University, and Aerodyne Research Inc. The study was supported by the National Natural Science Foundation of China and the Samsung Global Research Outreach Program. **Key Points:** - **Research Focus:** Molecular and seasonal characteristics of organic compounds in urban Beijing, specifically VOCs and their oxidation products. - **Techniques Used:** Vocus-PTR-TOF and CI-Orbitrap mass spectrometry. - **Findings:** - 512 organic molecules were identified in the m/z 50-200 range using Vocus-PTR-TOF, including sub-ppt level species and oxygenated molecules from both anthropogenic and biogenic sources. - 2403 OOMs were identified in the m/z 200-600 range using CI-Orbitrap, revealing clear homologous and oxygenation characteristics. - OOMs in Beijing are primarily from the oxidation of anthropogenic precursors. - New particle formation-related OOM dimers and important intermediates like organic radicals were also identified. - **Significance:** The study enhances the understanding of atmospheric organic molecule formation and evolution, crucial for air pollution management. - **Support and Collaboration:** Funded by the National Natural Science Foundation of China and the Samsung Global Research Outreach Program, with contributions from multiple universities and research institutions. **Paper Links:** - "Molecular and Seasonal Characteristics of Organic Vapors in Urban Beijing: Insights from Vocus-PTR Measurements" - [DOI: 10.5194/acp-24-13793-2024](http://doi.org/10.5194/acp-24-13793-2024) - "Resolving Atmospheric Oxygenated Organic Molecules in Urban Beijing Using Online Ultrahigh-Resolution Chemical Ionization Mass Spectrometry" - [DOI: 10.1021/acs.est.4c04214](https://pubs.acs.org/doi/10.1021/acs.est.4c04214)