AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Aerosol Analysis Using a Thermal-Desorption Mass Spectrometer (TD-MS) Modified from a Conventional Carbon Analyzer
XUFEI YANG, L.-W. Antony Chen, Xiaoliang Wang, Jerome Robles, John Watson, Judith Chow, Desert Research Institute
Abstract Number: 440 Working Group: Instrumentation and Methods
Abstract The thermal-desorption/mass spectrometry (TD-MS) analysis can fingerprint the composition of aerosols, thereby offering useful information to better understand the aerosols’ sources, properties and environmental impacts. This presentation describes our recent modification of a thermal/optical carbon analyzer to enable it for TD-MS analysis of aerosol-laden filter samples, in parallel to conventional organic carbon (OC) and elemental carbon (EC) analysis. In this system, a filter punch is heated following a pre-specified temperature program (e.g., IMPROVE_A) in the carrier gas of ultrapure helium. The evolved gas products first pass through an empty quartz tube heated at 650ºC, a typical vaporization temperature of aerosol mass spectrometer (AMS), and then proceed to an electron-impact mass selective detector (EI-MSD) via a heated transfer line (heated at 220ºC). Heating at 650ºC breaks low-volatility, large organic molecules into small fragments, thus reducing the loss of signals due to condensation along the transfer line. Preliminary results show that although the oxidation by trace oxygen (O2) in the carrier gas causes a certain loss of organic signals at higher temperatures (e.g., at > 480ºC), the system is able to generate aerosol mass spectra similar to AMS operated in the electron impaction mode and provide information related to sulfate, nitrate, ammonium, hydrocarbon-like and oxygenated organic matter (OM). A series of model compounds differing in chemical composition and O/C ratios, such as paraffin, oxalic acid, sucrose, levoglucosan, PAHs, proteins/amino acids, humic acids, ammonium nitrate and ammonium sulfate, as well as real-world source (e.g., mobile exhausts and biomass burning smoke) and ambient samples have been tested. The TD/MS spectra will be presented, and the feasibility of using the spectra to estimate the OM/OC ratio and source contributions will be discussed.