Advanced Method Unveils Diverse Pollutants in Beijing’s Air


A recent study conducted in Beijing, China, presented a novel method involving LC–MS/MS, UAE, and online SPE for characterizing environmental pollutants.

Beijing, China, is known for its poor air quality. Because of a combination of being the world’s largest greenhouse gas emitter and having many coal plants in its metropolitan area, Beijing is one of the most polluted cities, with hazardous PM2.5 particles more than 20 times higher than the guidelines established by the World Health Organization (WHO) (1).

Beijing | Image Credit: © Gang -

Beijing | Image Credit: © Gang -

As a result of this issue, scientists in China are searching for ways to test air quality in Beijing and across the globe. A recent study published in Chromatographia explores a novel process involving ultrasound-assisted extraction (UAE), online solid phase extraction (online SPE), and liquid chromatography–tandem mass spectrometry (LC–MS/MS) (2).

Led by Chao Wang from the China National Environmental Monitoring Centre, the research team deployed this highly sensitive method to determine 17 nitrated and oxygenated polycyclic aromatic hydrocarbons (NPAHs and OPAHs) in PM2.5. Using UAE, online SPE, and LC–MS/MS required significant refinement. The researcher’s methodology covered a spectrum of parameters, which include solvents and times used in UAE, extract filtering, online SPE conditions, and LC–MS settings (2). By optimizing the method for these parameters, the research team achieved isomeric separation and detection of mononitro-PAHs, dinitro-PAHs, and OPAHs. This was made possible by leveraging the proposed MS/MS fragmentation pathway in negative mode atmospheric pressure chemical ionization (2).

The research team used a method that had an online SPE advantage, which enabled the attainment of low limits of detection for NPAHs (ranging from 0.001 to 0.042 μg/L) and OPAHs (ranging from 0.01 to 0.038 μg/L) (2). Moreover, the recovery rates, spanning from 64% to 108% at three spiking levels, exhibited commendable relative standard deviations (RSDs) of 3% to 23% (2).

Notably, this study marks one of the first applications of the LC–MS methodology for the quantification of three carcinogenic dinitro-PAHs – specifically, 1,3-dinitropyrene, 1,6-dinitropyrene, and 1,8-dinitropyrene – within atmospheric PM2.5 (2).

The researchers deployed this method twice in Beijing: once in the summer, and once in the winter, with the goal being to determine the concentrations of various NPAHs and OPAHs in PM2.5 samples. The findings revealed concentrations ranging from ∑NPAH: 9.4 to 303.3 pg m−3 and ∑OPAHs: 125.2 to 1948.1 pg m−3, painting a comprehensive picture of the diverse pollutants present in the capital’s air (2).

The new methodology helps us to understand and improve the monitoring of air quality in urban areas and advances environmental science applications by offering scientists another roadmap to quantify pollutants in the air.

This article was written with the help of artificial intelligence and has been edited to ensure accuracy and clarity. You can read more about our policy for using AI here.


(1) Walsh, M. China's smog problem explained. Published November 1, 2023. (Accessed 21 November 2023). Available at:

(2) Wang, C.; Zhu, W.; Shi, Z.; Li, J. A Sensitive Online SPE-LC–APCI–MS/MS Method for Simultaneous Determination of 17 Nitrated and Oxygenated Polycyclic Aromatic Hydrocarbons in Atmospheric Particulate Matter. Chromatographia 2023, 86, 677–688.