State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, 100084 Beijing, China.
Chemistry Department, University of California, Irvine, California 92697, United States.
Environ Sci Technol. 2021 Mar 2;55(5):2859-2868. doi: 10.1021/acs.est.0c06053. Epub 2021 Feb 12.
Ultrafine particles (UFPs) dominate the particle number population in the urban atmosphere and revealing their chemical composition is important. The thermal desorption chemical ionization mass spectrometer (TDCIMS) can semicontinuously measure UFP composition at the molecular level. We modified a TDCIMS and deployed it in urban Beijing. Radioactive materials in the TDCIMS for aerosol charging and chemical ionization were replaced by soft X-ray ionizers so that it can be operated in countries with tight regulations on radioactive materials. Protonated -methyl-2-pyrrolidone ions were used as the positive reagent ion, which selectively detects ammonia and low-molecular weight-aliphatic amines and amides vaporized from the particle phase. With superoxide as the negative reagent ion, a wide range of inorganic and organic compounds were observed, including nitrate, sulfate, aliphatic acids with carbon numbers up to 18, and highly oxygenated CHO, CHON, and CHOS compounds. The latter two can be attributed to parent ions or the decomposition products of organonitrates and organosulfates/organosulfonates, respectively. Components from both primary emissions and secondary formation of UFPs were identified. Compared to the UFPs measured at forest and marine sites, those in urban Beijing contain more nitrogen-containing and sulfur-containing compounds. These observations illustrate unique features of the UFPs in the urban environment and provide insights into their origins.
超细颗粒（UFPs）在城市大气中占据了颗粒数量的主导地位，揭示其化学成分非常重要。热解吸化学电离质谱仪（TDCIMS）可以在分子水平上半连续地测量 UFP 的组成。我们对 TDCIMS 进行了改进，并将其部署在北京的城市地区。用于气溶胶充电和化学电离的 TDCIMS 中的放射性物质被软 X 射线离子源取代，因此它可以在对放射性物质有严格规定的国家运行。质子化的 -甲基-2-吡咯烷酮离子被用作正试剂离子，它选择性地检测从颗粒相中蒸发的氨和低分子量脂肪族胺和酰胺。使用超氧化物作为负试剂离子，可以观察到广泛的无机和有机化合物，包括硝酸盐、硫酸盐、碳数高达 18 的脂肪酸，以及高度含氧的 CHO、CHON 和 CHOS 化合物。后两者可以归因于有机硝酸盐和有机硫酸盐/有机磺酸盐的母体离子或分解产物。识别出了 UFPs 的初级排放和二次形成的成分。与在森林和海洋地点测量的 UFPs 相比，北京城市地区的 UFPs 含有更多的含氮和含硫化合物。这些观察结果说明了城市环境中 UFPs 的独特特征，并为它们的来源提供了一些见解。
