AVS 64th International Symposium & Exhibition
    Applied Surface Science Division Monday Sessions
       Session AS+BI-MoA

Paper AS+BI-MoA3
Does Time Play a Role in Glyoxal and Hydrogen Peroxide Photochemical Aging?

Monday, October 30, 2017, 2:20 pm, Room 13

Session: Practical Surface Analysis: Complex, Organic and Bio-systems
Presenter: Fei Zhang, Pacific Northwest National Laboratory
Authors: F. Zhang, Pacific Northwest National Laboratory
X.F. Yu, Pacific Northwest National Laboratory
X. Sui, Pacific Northwest National Laboratory
J.M. Chen, Fudan University
Z.H. Zhu, Pacific Northwest National Laboratory
X.Y. Yu, Pacific Northwest National Laboratory
Correspondent: Click to Email
Aqueous surfaces consisting of glyoxal and hydrogen peroxide (H2O2) after photochemical aging have been studied in a microfluidic reactor (System for Analysis at the Liquid Vacuum Interface, SALVI) by in situ liquid Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). Positive and negative ion mode mass spectra provide complementary information of the surface reactions. Compared with previous results using bulk solutions, our unique liquid surface molecular imaging approach makes it possible to observe glyoxal hydration (i.e., first and secondary products, hydrates), oxidation products (i.e., glyoxylic acid, oxalic acid, formic acid, malonic acid, tartaric acid), oligomers (i.e., C7H11O9+, C6H5O10-), water clusters (i.e., (H2O)nH+, n< 43, (H2O)nOH-, n< 44), and cluster ions (i.e.,C6H17O12+, C7H9O11-) with submicrometer spatial resolution. Spectral principal component analysis (PCA) is used to determine similarities and differences among photochemical aging samples ranging from 15 minutes to 8 hours. The oxidation products such as glyoxylic acid, glycolic acid, and tartaric acid tend to peak at around between 30 min and 1 h. UV aging; while oligomers and large water clusters (i.e., (H2O)22OH-, (H2O)23OH-,(H2O)24OH-) form significantly at about 3 h. The oligomer formation reaches its maximum at 4 h., and reduces afterwards. Large water clusters (n> 15) become more significant as photochemical aging progresses, indicating more hydrophobicity at the aqueous surface as predicted by molecular dynamic simulation in earlier works. SIMS three-dimensional (3D) chemical mapping enables visualization of the surface mixing state at the molecular level. We have presented the temporal progression of the 3D surface mixing state of various products from glyoxal and hydrogen peroxide oxidation for the first time. Such physical measurements pave a new way to investigate complex surface reaction mechanisms as an important source of aqueous secondary organic aerosol (SOA) formation in atmospheric chemistry.