Development of a Micro Orifice Volatilization Impactor - Chemical Ionization -High Resolution Time of Flight Mass Spectrometer (MOVI-CI-HToFMS) for In-situ Detection of Gas and Particle Phase Organic Matter

REDDY L. N. YATAVELLI(1), Joel Thornton(2), Joel Kimmel(3), Timothy Bertram(4), Mark Gonin(5), Doug Worsnop(6)

(1) University of Washington, Seattle, WA (2) University of Washington, Seattle, WA (3) Aerodyne Research Inc, Billerica, MA and Tofwerk AG, Switzerland (4) University of California, San Diego, CA (5) Tofwerk AG, Switzerland (6) Aerodyne Research Inc, Billerica, MA

     Abstract Number: 783
     Last modified: May 14, 2010

Abstract
We discuss the development and characterization of a new technique for in-situ gas and particulate organic matter composition measurements. The technique, based on chemical ionization (CI), high-resolution time-of-flight mass spectrometry (HTOF-MS) utilizes a Micro-Orifice Volatilization Impactor (MOVI) to concentrate sub-micron particles by inertial collection on an impactor surface while simultaneously assaying gas-phase composition. The collected particles are subsequently analyzed by temperature-programmable thermal desorption CI-HTOF-MS.

The reagent ion chosen for CI as part of these initial characterization studies is the acetate anion (CH3C(O)O-, m/z 59), which reacts selectively via proton transfer with compounds that are stronger gas-phase acids than acetic acid [Veres, 2009]. Preliminary calibrations show that the CI-HTOF-MS achieves a sensitivity of ~ 100 counts/sec/pptv towards small gas-phase acids (e.g. formic acid), and sub-nanogram detection limits for low-volatility dicarboxylic acids deposited on the MOVI. The resolving power (m/delta m) approaches 4000 in the lower resolution V-mode, and >5000 in the higher resolution W-mode. We illustrate the unique advantages of this instrument via detection and volatility characterization of high molecular weight multi-functional carboxylic acids present in secondary organic aerosol generated from alpha-pinene photo-oxidation. We conclude with preliminary data from the first field deployment of the instrument as part of the CalNex-2010 campaign at the Pasadena, CA supersite.