HR: 1340h
AN: A13C-0926 INVITED     [Abstracts]
TI: Chemical Ionization Mass Spectrometry Techniques for Measurements of Gas-Phase Ammonia
AU: * Nowak, J B
EM: John.Nowak@noaa.gov
AF: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309 United States
AU: * Nowak, J B
EM: John.Nowak@noaa.gov
AF: NOAA Aeronomy Laboratory, 325 Broadway, Boulder, CO 80305 United States
AU: Neuman, J A
EM: Andy.Neuman@noaa.gov
AF: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309 United States
AU: Neuman, J A
EM: Andy.Neuman@noaa.gov
AF: NOAA Aeronomy Laboratory, 325 Broadway, Boulder, CO 80305 United States
AU: Yoshida, K
EM: kyoshida@hmc.edu
AF: Harvey Mudd College, 301 E. 12th Street, Claremont, CA 91711 United States
AU: Ryerson, T B
EM: Thomas.B.Ryerson@noaa.gov
AF: NOAA Aeronomy Laboratory, 325 Broadway, Boulder, CO 80305 United States
AU: Huey, L G
EM: Greg.Huey@eas.gatech.edu
AF: School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332 United States
AU: Tanner, D J
EM: Tanner@eas.gatech.edu
AF: School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332 United States
AU: Sjostedt, S J
EM: steve.sjostedt@eas.gatech.edu
AF: School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332 United States
AU: Hubler, G
EM: Gerhard.Hubler@noaa.gov
AF: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309 United States
AU: Hubler, G
EM: Gerhard.Hubler@noaa.gov
AF: NOAA Aeronomy Laboratory, 325 Broadway, Boulder, CO 80305 United States
AU: Fortin, T J
EM: Tara.J.Fortin@noaa.gov
AF: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309 United States
AU: Fortin, T J
EM: Tara.J.Fortin@noaa.gov
AF: NOAA Aeronomy Laboratory, 325 Broadway, Boulder, CO 80305 United States
AU: Sueper, D J
EM: Donna.T.Sueper@noaa.gov
AF: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309 United States
AU: Sueper, D J
EM: Donna.T.Sueper@noaa.gov
AF: NOAA Aeronomy Laboratory, 325 Broadway, Boulder, CO 80305 United States
AU: Fehsenfeld, F C
EM: Fred.C.Fehsenfeld@noaa.gov
AF: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309 United States
AU: Fehsenfeld, F C
EM: Fred.C.Fehsenfeld@noaa.gov
AF: NOAA Aeronomy Laboratory, 325 Broadway, Boulder, CO 80305 United States
AB: Chemical Ionization Mass Spectrometry (CIMS) can be a highly selective technique with fast time response for measuring many atmospheric trace gases (e.g., hydroxyl radical (OH), sulfuric acid (H₂SO₄), nitric acid (HNO₃)). CIMS is highly versatile and has been used under a wide variety of conditions with many different ion-molecule detection schemes, even for detecting the same molecule. Because of its high proton affinity (853.6 kJ/mol), ammonia (NH₃) is another ideal candidate for detection by CIMS. NH₃, the dominant gas-phase base in the atmosphere, is a precursor of ammonium nitrate and ammonium sulfates, compounds that are important constituents of airborne fine particulate matter that affect air quality. The characterization of three NH₃ CIMS instruments: an atmospheric pressure ionization instrument and a low-pressure flow tube reactor instrument, both utilizing protonated ethanol cluster ion chemistry, and a different low-pressure flow tube reactor instrument using protonated acetone dimer ion chemistry, is presented here. Instrument performance is assessed using ambient data from both ground-based and airborne field programs to examine detection sensitivity, background signal, and time response. Laboratory characterization of different inlet materials is also presented. All three instruments used PFA Teflon sampling inlets. Instrumental backgrounds were determined by scrubbing NH₃ from ambient air using silicon phosphates that release phosphoric acid when exposed to ambient levels of humidity. Standard addition calibrations were performed using NH₃ permeation devices whose output was determined via 185nm optical absorption. Regardless of CIMS technique or ion chemistry used, the observed detection sensitivities were all adequate for detecting changes in NH₃ at the 10 pptv level on a 1s timescale. The time responses, defined by a 1/e² decay in the calibration signal, ranged from 5s to 45s for the different sampling inlet configurations and are rapid enough for use on mobile platforms and for studying atmospheric processes such as aerosol nucleation. The absolute level of and variability in the instrument background was found to be more critical to accurate NH₃ measurements than were differences between CIMS techniques or ion chemistries. Over the course of a field deployment the background levels ranged from 0.1 to 1 ppbv. The short time scale (~15 minute) variability in the instrument background for each instrument ranged from 0.05 to 0.125 ppbv. A major component of the background signal in all cases was the release of NH₃ from instrument inlet surfaces, and these surface interactions varied with changing ambient conditions. Both the absolute level and the variability in the instrumental background need to be reduced and controlled to take advantage of the CIMS detector sensitivity and make fast, accurate, and precise measurements of NH₃ at the 0.1 pptv level.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0365 Troposphere: composition and chemistry
DE: 0394 Instruments and techniques
DE: 0399 General or miscellaneous
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005