Signal processing and calibration procedures for in situ diode-laser absorption spectroscopy.

Results on NO2 instruments are reported from the NASA Global Tropospheric Experiment Chemical Instrumentation Test and Evaluation 2 (CITE 2) program in summer 1986. The instruments tested were (1) a two-photon LIF system using a laser for NO2-NO photolysis, (2) a chemiluminescence (CL) detector using FeSO4 for NO2-NO conversion, (3) a CL detector using an arc lamp for NO2-NO photolysis, and (4) a tunable-laser-diode multipath-absorption system. The procedures for the CITE 2 ground-based and flight tests are described in detail, and the results are presented in extensive graphs. Instrument (2) was eliminated because the FeSO4 converted atmospheric PAN to NO, resulting in spuriously high NO2 values. The remaining instruments gave readings in 30-40-percent agreement at NO2 mixing ratios of 100-200 parts per trillion by volume (pptv). At ratios below 50 pptv, the correlation among the measurements was very poor, with a tendency for system (4) to give higher values than (1) or (3).

/pdf/an-intercomparison-of-airborne-nitrogen-dioxide-instruments-1h4xynwyza.pdf

An Intercomparison of Airborne Nitrogen Dioxide Instruments

A versatile and integrated tunable diode laser system for high precision measurements of the important sulfur gas carbonyl sulfide is described. We explicitly address some of the major factors affecting tunable diode laser measurement precision as well as accuracy and have implemented a number of new features for increased system control and versatility. The system described herein provides the capability for measuring ambient concentrations of this gas with a precision in the range from ±0.3 to ±1% over time periods of many hours. Such a precision provides us with an important new capability for measuring true spatial and temporal variations of carbonyl sulfide in the atmosphere.

Versatile integrated tunable diode laser system for high precision: application for ambient measurements of OCS

This paper provides the rationale, objectives, approach, and a brief description of the instrumentation included in the second airborne Chemical Instrumentation Test and Evaluation (CITE 2) mission conducted on NASA's Electra aircraft. CITE 2 intercompared data from instruments measuring NO2, HNO3, and PAN in the troposphere. This study, conducted in August 1986, encountered marine and continental air with free tropospheric mixing ratios of NO2, HNO3, and PAN typically less than 120, 150, and 200 parts per trillion by volume, respectively.

Operational overview of NASA GTE/CITE 2 airborne instrument intercomparisons: Nitrogen dioxide, nitric acid, and peroxyacetyl nitrate

We present two new approaches in tunable diode laser absorption spectroscopy (TDLAS) for measuring the ratio of two components with high precision. These techniques, dual line fitting analysis and jump scanning, greatly extend the versatility and applicability of TDLAS. Three important applications for these approaches are discussed. In addition, we demonstrate the capability to quantify features that are different in amplitude by a factor of 22.4 with a precision of 0.3%. Such a precision is also achieved for features that are different in amplitude by a factor of 12.9 and separated by 0.2363 cm(-1). Both jump scanning and dual line fitting analysis are being used on a routine basis in a laboratory kinetics study to measure simultaneously the concentrations of H(2)O and NO, whose features are separated by 0.4866 cm(-1).

Tunable diode laser ratio measurements of atmospheric constituents by employing dual fitting analysis and jump scanning

An NO2 calibration system, based on a permeation device and a two-stage dynamic dilution system, was designed, constructed, and characterized at the National Bureau of Standards. In this system, calibrant flow entering the second stage was controlled without contacting a metal flow controller, and permeation oven temperature and flow were continuously maintained, even during transport. The system performance and the permeation emission rate were characterized by extensive laboratory tests. This system was capable of accurately delivering known NO2 concentrations in the ppbv and sub-ppbv concentration range with a total uncertainty of approximately 10 percent. The calibration system was placed on board NASA research aircraft at both the Wallops Island and Ames research facilities. There it was employed as the reference standard in NASA's Global Tropospheric Experiment/Chemical Instrumental Test and Evaluation 2 mission in August 1986.

Reference NO2 calibration system for ground-based intercomparisons during NASA's GTE/CITE 2 mission

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Reference NO2 calibration system for ground-based intercomparisons during NASA's GTE/CITE 2 mission