 |
| Titel |
Characterizing a Quantum Cascade Tunable Infrared Laser Differential Absorption Spectrometer (QC-TILDAS) for measurements of atmospheric ammonia |
| VerfasserIn |
R. A. Ellis, J. G. Murphy, E. Pattey, R. Haarlem, J. M. O'Brien, S. C. Herndon |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1867-1381
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 3, no. 2 ; Nr. 3, no. 2 (2010-03-30), S.397-406 |
| Datensatznummer |
250000972
|
| Publikation (Nr.) |
 copernicus.org/amt-3-397-2010.pdf |
|
|
|
|
|
| Zusammenfassung |
| A compact, fast-response Quantum Cascade Tunable Infrared Laser Differential
Absorption Spectrometer (QC-TILDAS) for measurements of ammonia (NH3)
has been evaluated under both laboratory and field conditions. Absorption of
radiation from a pulsed, thermoelectrically cooled QC laser occurs at
reduced pressure in a 0.5 L multiple pass absorption cell with an effective
path length of 76 m. Detection is achieved using a thermoelectrically-cooled
Mercury Cadmium Telluride (HgCdTe) infrared detector. A novel sampling inlet
was used, consisting of a short, heated, quartz tube with a hydrophobic
coating to minimize the adsorption of NH3 to surfaces. The inlet
contains a critical orifice that reduces the pressure, a virtual impactor
for separation of particles, and additional ports for delivering
NH3-free background air and calibration gas standards. The level of
noise in this instrument has been found to be 0.23 ppb at 1 Hz. The sampling
technique has been compared to the results of a conventional lead salt
Tunable Diode Laser Absorption Spectrometer (TDLAS) during a laboratory
intercomparison. The effect of humidity and heat on the surface interaction
of NH3 with sample tubing was investigated at mixing ratios ranging
from 30–1000 ppb. Humidity was seen to worsen the NH3 time response and
considerable improvement was observed when using a heated sampling line. A
field intercomparison of the QC-TILDAS with a modified Thermo 42CTL
chemiluminescence-based analyzer was also performed at Environment Canada's
Centre for Atmospheric Research Experiments (CARE) in the rural town of
Egbert, ON between May–July 2008. Background tests and calibrations using
two different permeation tube sources and an NH3 gas cylinder were
regularly carried out throughout the study. Results indicate a very good
correlation at 1 min time resolution (R2 = 0.93) between the two
instruments at the beginning of the study, when regular background
subtraction was applied to the QC-TILDAS. An overall good correlation of
R2 = 0.85 was obtained over the entire two month data set, where the
majority of the spread can be attributed to differences in inlet design and
background subtraction methods. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|