HR: 1340h
AN: A33B-1185    [Abstracts]
TI: A Micro-Orifice Volatilization Impactor coupled to a Chemical Ionization Mass Spectrometer for the detection of organic acids in atmospheric aerosol particles
AU: * Yatavelli, R L
EM: reddy@atmos.washington.edu
AF: Department of Atmospheric Sciences, 408 ATG, University of Washington, Seattle, WA 98195, United States
AU: Thornton, J A
EM: thornton@atmos.washington.edu
AF: Department of Atmospheric Sciences, 408 ATG, University of Washington, Seattle, WA 98195, United States
AB: Significant uncertainties related to sources and removal processes of particulate organic matter persist due, in part, to a poor understanding of the molecular-level composition. To address these issues, we are developing a novel technique that couples a micro-orifice volatilization impactor (MOVI) to a chemical ionization mass spectrometer (CIMS) for fast, in situ measurements of specific organic acids expected to be in atmospheric particles. The MOVI-CIMS process has three steps: 1) aerosol collection by inertial impaction, 2) volatilization and sample transfer, and 3) chemical ionization and detection using a quadrupole mass spectrometer. We present results from laboratory characterization of two MOVI designs, one operating at low pressure (60 Torr) and the other at near ambient pressure. The low-pressure impactor has a theoretical cut point of 40nm while the atmospheric pressure impactor (API) has a theoretical cut point of 280nm with a pressure drop of less than 5%. We compare the advantages and disadvantages of these two designs in terms of typical atmospheric particle size distributions. Experimental tests of their theoretical cut-points are used to assess the importance of jet-to- plate distance and particle bounce. In addition, we demonstrate the utility of the MOVI-CIMS technique by employing it in studies of heterogeneous oxidation of particle organics and of secondary organic aerosol formation from biogenic hydrocarbon oxidation. Based on typical signal-to-noise ratio, the MOVI-CIMS demonstrates a detection limit of ~50 ng for monocarboxylic acids when using the LPI version and the iodide ion as a chemical ionization reagent. Preliminary results suggest even lower detection limits are possible with other reagent ions.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting