Development and application of a GC system for NMHC analyses of air samples from the CARIBIC aircraft project [Elektronische Ressource] / Bohdan Řanda

Informations

• Publié par: johannes_gutenberg-universitat_mainz
• Publié le: 01 janvier 2008
• Nombre de lectures: 28
• Langue: English
• Poids de l'ouvrage: 7 Mo

Extrait

Development and application of a GC system for
NMHC analyses of air samples from the
CARIBIC aircraft project






Dissertation
zur Erlangung des Grades
„Doktor der Naturwissenschaften“

am Fachbereich Chemie
der Johannes Gutenberg-Universität in Mainz















Bohdan Řanda

geb. in Kutna Hora / Tschechische Republik
Mainz, 2007






































Abstract

The subject of this thesis is the development of a Gaschromatography (GC)
system for non-methane hydrocarbons (NMHCs) and measurement of samples within
the project CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere
Based on an Instrument Container, www.caribic-atmospheric.com). Air samples
collected at cruising altitude from the upper troposphere and lowermost stratosphere
contain hydrocarbons at low levels (ppt range), which imposes substantial demands on
detection limits. Full automation enabled to maintain constant conditions during the
sample processing and analyses. Additionally, automation allows overnight operation
thus saving time. A gas chromatography using flame ionization detection (FID)
together with the dual column approach enables simultaneous detection with almost
equal carbon atom response for all hydrocarbons except for ethyne.
The first part of this thesis presents the technical descriptions of individual parts of the
analytical system. Apart from the sample treatment and calibration procedures, the
sample collector is described. The second part deals with analytical performance of the
GC system by discussing tests that had been made. Finally, results for measurement
flight are assessed in terms of quality of the data and two flights are discussed in detail.
Analytical performance is characterized using detection limits for each compound,
using uncertainties for each compound, using tests of calibration mixture conditioning
and carbon dioxide trap to find out their influence on analyses, and finally by
comparing the responses of calibrated substances during period when analyses of the
flights were made. Comparison of both systems shows good agreement. However,
because of insufficient capacity of the CO trap the signal of one column was 2
suppressed due to breakthroughed carbon dioxide so much that its results appeared to
be unreliable.
Plausibility tests for the internal consistency of the given data sets are based on
common patterns exhibited by tropospheric NMHCs. All tests show that samples from
the first flights do not comply with the expected pattern. Additionally, detected alkene
artefacts suggest potential problems with storing or contamination within all
measurement flights. Two last flights # 130-133 and # 166-169 comply with the tests
therefore their detailed analysis is made. Samples were analyzed in terms of their origin
(troposphere vs. stratosphere, backward trajectories), their aging (NMHCs ratios) and
detected plumes were compared to chemical signatures of Asian outflows.
In the last chapter a future development of the presented system with focus on
separation is drawn. An extensive appendix documents all important aspects of the
dissertation from theoretical introduction through illustration of sample treatment to
overview diagrams for the measured flights.





Content

Content

CONTENT ...................................................................................................................... I
LIST OF FIGURES .................................................................................................... III
LIST OF TABLES ........................................................................................................V
APPENDIX .................................................................................................................VII
ABBREVIATIONS ..................................................................................................... IX
1. INTRODUCTION................................................................................................ - 1 -
1.1 OBJECTIVE OF THE WORK ..............................................................................................- 1 -
1.2 CARIBIC.......................................................................................................................- 1 -
2. NMHCS IN THE ATMOSPHERE..................................................................... - 3 -
2.1 NMHCS: SOURCES, ATMOSPHERIC CHEMISTRY, ABUNDANCE OF.................................- 3 -
ALKENES AND ALKADIENES .................................................................................................- 3 -
2.2 MEASUREMENT TECHNIQUES FOR NMHCS ..................................................................- 9 -
3. EXPERIMENTAL ............................................................................................. - 17 -
3.1 ANALYTICAL SYSTEM..................................................................................................- 17 -
3.1.1 The apparatus description............................................................................................... - 17 -
3.1.2 The gas chromatograph - 20 -
3.1.2.1 The detector........................................................................................................... - 21 -
3.1.2.2 The FID................................................................................................................. - 22 -
3.1.2.3 The used GC.......................................................................................................... - 25 -
3.1.3 The columns ................................................................................................................... - 26 -
3.1.3.1 The separation....................................................................................................... - 28 -
3.1.3.2 The used columns - 31 -
3.1.4 The gas supply................................................................................................................ - 33 -
3.1.5 The description of instrument components..................................................................... - 35 -
3.1.5.1 The CO and H O traps ......................................................................................... - 35 - 2 2
3.1.5.2 The enrichment trap (PF) ...................................................................................... - 36 -
3.1.5.3 The cryo-focusing trap (KF) ................................................................................. - 39 -
3.1.5.4 The dewars ............................................................................................................- 41 -
3.1.5.5 The pistons.. - 44 -
3.1.5.6 The mass flow controllers ..................................................................................... - 44 -
3.1.5.7 The V25 ................................................................................................................ - 45 -
3.2 ANALYTICAL PROCEDURE ...........................................................................................- 46 -
3.2.1 The automation............................................................................................................... - 47 -
3.2.1.1 Building the menu................................................................................................. - 47 -
3.2.1.2 The Data-option.................................................................................................... - 48 -
3.2.1.3 The Param - 50 -
3.2.1.4 The Control-option................................................................................................ - 51 -
3.2.2 The system procedure.- 52 -
3.3 CALIBRATION ..............................................................................................................- 58 -
3.3.1 The calibration curves .................................................................................................... - 58 -
3.3.2 The peak identification.. - 59 -
3.3.3 The dilution .................................................................................................................... - 59 -
3.3.4 The determination of the sample volume ....................................................................... - 60 -
3.4 AIR SAMPLING .............................................................................................................- 64 -
4. RESULTS AND DISCUSSION......................................................................... - 67 -

I Content

4.1 ANALYTICAL PERFORMANCE...................................................................................... - 67 -
4.1.1 Calibration function ........................................................................................................- 67 -
4.1.2 Conditioning of the calibration mixture..........................................................................- 75 -
4.1.3 Uncertainty...........................................................................