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.
|