Abstract View
Development of a Higher Mass Resolution Aerosol Chemical Speciation Monitor
PHILIP CROTEAU, Benjamin A. Nault, Leah Williams, Manjula Canagaratna, Harald Stark, Donna Sueper, John Jayne, Douglas Worsnop, Aerodyne Research, Inc.
Abstract Number: 490
Working Group: Instrumentation and Methods
Abstract
Over the past ten years, the aerosol chemical speciation monitor (ACSM) has become a valuable tool for understanding aerosol chemistry by enabling measurements of long-term trends in particle composition with high temporal resolution. However, the low mass resolution of the ACSM detector limits the chemical specificity of the measured mass spectra when compared with, for example, the high-resolution time-of-flight aerosol mass spectrometer (HTOF-AMS). Specifically, the detection limit of ammonium with the standard unit mass resolution ACSM is much higher than with HTOF-AMS because its largest signals, NH2+ at m/z 16 and NH3+ at m/z 17, are measured against the much larger isobaric signals of O+ and OH+ from oxygen and water. Furthermore, ACSM organic aerosol chemical composition measurements are limited by their inability to directly distinguish oxygen-bearing organic fragments from hydrocarbons, such as C2H3O+ and C3H7+ at m/z 43. Here we present instrumental details and data from a new version of the ACSM, the TOF-ACSM X, designed to mitigate these limitations. The TOF-ACSM X detector is a mass spectrometer designed to be robust and capable of long-term, unattended operation, like the standard ACSM, but to also provide enough mass resolution to dramatically improve the quantification of ammonium and to allow for more accurate quantification of the elemental ratios O:C and H:C in the organic aerosol.