Ozone and Carbon Dioxide Tracer Experiment
Dr. Melody A. Avery, Ms. Stephanie A. Vay, NASA Langley Research Center
During the NASA TRACE-P mission we will make and interpret accurate, high precision measurements of ozone (O3) and carbon dioxide (CO2) from the NASA DC-8 and P-3B aircraft in outflow from the Asian continent in the troposphere over the western Pacific Ocean. Ozone is a photochemical oxidant and CO2 a useful tracer for transport in the troposphere. Both chemical species are radiatively active and characterization of their distribution in this rapidly industrializing region of the world is critical to accurately quantifying the total global oxidizing and warming potential. Fast-response data from the P-3B will be used to estimate fluxes and deposition rates, critical to chemical budget evaluation. Our instruments have flown successfully on both planes during numerous previous NASA missions.
Ozone:
Ozone is measured by reaction of sampled air with pure reagent nitric oxide (NO)
to produce excited state NO2. Near-infrared
light emitted by relaxation of the excited NO2 is measured with a
sensitive photocathode and photomultiplier tube and is proportional to the
amount of O3 in the sampled air. We propose to implement both
detectors with forward-facing Teflon-lined inlets that we have tested and found
to be insensitive to aircraft attitude. For the TRACE-P mission we will upgrade
a PMT cooler, amplifiers and signal conditioning circuitry to lower noise in our
fast response measurements. Ozone
data will be reported at 1 Hz in real-time to the mission scientist on the
plane.
Carbon Dioxide:
Carbon dioxide measurements will be provided by modified Li-COR model
6252 non-dispersive infrared (NDIR) spectrometers operated within constant
temperature, pressure, and flow sampling systems.
The instruments are composed of dual 11.9 cm3
volume sample/reference cells; a feedback stabilized infrared source; 500
Hz chopper; thermoelectrically-cooled solid state PbSe detector; and a narrow
band (150 nm) interference filter centered on the 4.26 mm CO2
absorption band. Using synchronous
signal detection techniques, they operate by sensing the differential absorption
between continuously flowing sample and reference gases.
Air is sampled through Rosemount inlet probes and dried to remove H2O(v).
Frequent calibrations are performed to achieve both high precision and
accuracy.
Instrument
Performance Characteristics;
| |
Ozone |
Carbon
Dioxide |
| Technique |
Chemiluminescense |
Non-dispersive infrared
spectrometer |
| Dynamic
Range |
0.5 to 1500 ppbv |
0 to 3000 ppmv |
| Response
Time |
2-3 Hz |
1 Hz, DC-8; 1 and 10 Hz, P-3B |
| Accuracy |
3% or 2 ppbv |
0.25 ppmv |
| Precision
(1s) |
1% or 0.5 ppbv (1 Hz) |
0.07 ppmv (1 Hz); 0.25 ppmv (10
Hz) |
| Data
Rate |
6 Hz, DC-8; 22 Hz, P-3B |
6 Hz, DC-8; 22 Hz, P-3B |
| Data
Reporting |
1 Hz, DC-8 and P-3B; 10 Hz, P-3B (post-mission) |
1 Hz, DC-8 and P-3B; 10 Hz, P-3B (post-mission) |
Analysis: Post-mission analyses will focus upon establishing background spatial distributions of CO2 and O3 over the region and examining how transport and regional source/sink processes influence these distributions. We will compare our O3 measurements to model projections to estimate the extent of stratospheric/tropospheric exchange and we will characterize variability associated with polar and subtropical jets to assess the potential impact on limb-scanning satellites retrievals. We plan to investigate CO2 sources by examining chemical correlations for “fingerprints” that correspond to emissions from biomass burning, agriculture, industry, or trop/strat exchange. We will examine geographic and vertical gradients in combination with air mass back-trajectory information to determine possible source regions/processes. Finally, we will contrast our TRACE-P data with observations from earlier (PEM West) missions to determine the impact of substantially increased industrialization.