AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Influence of Solvent Residue from Aerosol Generation on Ion Properties and Aerosol Charging in a Soft X-ray Neutralizer
XIAOTONG CHEN, Dongsen Yang, Runlong Cai, Qiang Zhang, Jun Zheng, Jingkun Jiang, Tsinghua University
Abstract Number: 53 Working Group: Instrumentation and Methods
Abstract Solutions, such as di-octyl sebacate (DOS) in isopropyl alcohol (IPA), tetra-heptyl ammonium bromide (THABr) in methanol and sodium chloride in water, are often used to generate standard aerosols through atomization or electrospray. After aerosol generation, some solvent residue remains in the carrier gas. Upon entering the aerosol neutralizer, solvent residue may participate in the dynamic processes of ion generation and aerosol charging. In this study, we tested the influence of IPA, methanol, and water vapor on neutralizer ion properties, charging fractions, and subsequent size distribution measurement. A bubbler was used to add different levels of solvents into nitrogen (99.999%), simulating solvent residue in the carrier gas when generating aerosols. A half-mini DMA (long/thin type) and an electrometer (Model 3068B, TSI, Inc.) were used to measure ion mobilities downstream a soft X-ray aerosol neutralizer (Model 3088, TSI, Inc.). Ion compositions were characterized by an atmospheric pressure interface high-resolution time-of-flight mass spectrometer (APi-HR-ToFMS). Based on these measured ion parameters, charging fractions were estimated using Fuchs diffusion charging theory. DOS aerosol size distributions with different levels of solvent residue were also measured. When increasing the concentration of IPA or methanol vapour in the carrier gas, the mobilities of both positive and negative ions were found decreased, indicating that organic vapour molecules might have participated in ionization reactions. An increase in water vapour concentration did not influence positive ions significantly, while the mobilities of negative ions were found increased, possibly due to the promotion of NO$_(3)$^(-) generation by adding water vapour. Significant influences on DOS size distribution measurement were observed when there are IPA vapour left in the carrier gas.