Stratospheric ozone was measured from a balloon utilizing an ultraviolet absorption cell. The ambient air was sampled by means of an aspirator attached to the output end of the optical cell. A nominal ozone distribution was obtained from 16 km to the float altitude of 38 km

Ashenfelter, T. E.

Hilsenrath, E.

English

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, . -* 
A BALLOON OZONE MEASUREMENT 
UTILIZING A N  OPTICAL ABSORPTION CELL 
A N D  A N  EJECTOR AIR SAMPLER 
Ernest Hilsenrath and Thomas E.  Ashen filter 
Goddard Space Flight Center 
Greenbelt, Md.  20771 
N A T I O N A L  AERONAUTICS A N D  SPACE A D M I N I S T R A T I O N  W A S H I N G T O N ,  JULY 1976 
\ &  
https://ntrs.nasa.gov/search.jsp?R=19760022777 2020-03-22T13:10:10+00:00Z
1; ReporNo. 2. Government Accession No. 
NASA TN D-8281 
4. Ti t le and Subtitle 
A Balloon Ozone Measurement Utilizing an Optical 
Absorption Cell and an Ejector Air Sampler 
Ernest Hilsenrath and Thomas E. Ashenfelter 
Goddard Space Flight Center 
Greenbelt, Maryland 2077 1 
7. Author(s) 
9. Performing Organization Name and Address 
2. Sponsoring Agency Name and Address 
National Aeronautics and Space Administration 
Washington, D.C. 20546 
5. Supplementary Notes 
6. Abstract 
--1 . .  3. Recipient's Cotolog No. 
5. Report Date 
J u l y ,  1976 
6. Performing OrgonizotionCode 
912 
8. Performing Organization Report No. 
G-7698 
176-10-41 
10. Work Unit No. 
11. Contract or Grant NO. 
13. Type of Report and Period Coverec 
Technical Note 
14. Sponsoring Agency Code 
Stratospheric ozone was measured, in situ , from a balloon utilizing an ultraviolet 
absorption cell. The instrument was carried to  a 38-km float altitude from Holloman 
Air Force Base, Albuquerque, New Mexico on June 27, 1974. The ambient air was 
sampled by means of an aspirator attached to  the output end of the optical cell. 
A nominal ozone distribution was obtained from 16 km to the float altitude of 
38 km. 
'. Key Words (Selected by Author(s)) 
Ozone, Balloon measurement, 
Stratosphere 
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This document makes use of international metric units according to the 
Systeme Internationale d’Unites (SI). In certain cases, utility requires the 
retention of other systems of units in addition to  the SI units. The con- 
ventional units stated in parentheses following the computed SI equivalents 
are the basis of the measurements and calculations reported. 
.. 
11 
CONTENTS 
Page 
ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
INSTRUMENTATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
FLIGHT RESULTS . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
CONCLUSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
... 
111 
A BALLOON OZONE MEASUREMENT UTILIZING 
AN OPTICAL ABSORPTION CELL AND AN 
EJECTOR AIR SAMPLER 
Ernest Hilsenrath 
Goddard Space Flight Center 
Greenbelt, Maryland 
Thomas E. Asheiifelter 
NOAA Air Resources Laboratory 
Silver Spring, Maryland 
INTRODUCTION 
Ozone in the lower stratosphere has been routinely measured by electrochemical (Reference 
1) and chemiluminescent (Reference 2) detectors attached to  radiosondes. The upper 
limit of these soundings is determined by the attainable height of the balloon and the 
sampling efficiency of the mechanical air pump. At high altitudes the data from these 
sondes becomes uncertain (Reference 3).  Rocket techniques are also employed to  measure 
the vertical ozone distribution in the upper atmosphere (References 4 and 5). 
The objective of the experiment described herein was to  measure the diurnal variability of 
ozone at constant altitude above the concentration maximum. Since the variability was 
expected to  be relatively small, the instrument was required to be precise as well as accurate. 
This experiment also involved the first attempt to utilize an air ejector pump (Reference 6) 
for continuous sampling of stratospheric air for trace gas measurements. A night launch 
and balloon float during sunrise had been planned, but,  because of weather conditions, the 
launch occurred during the day. 
I NSTRUM ENTATl ON 
Ozone Detector 
A Dasibi Corporation optical ozone monitor (Reference 7) was modified to be compatible 
with a balloon gondola prepared by the University of Denver (figure 1). The instrument 
was packaged to withstand the thermal and pressure environment of an ascent to  40 km, as 
well as to  be compatible with the gondola electrical support system. Additional housekeeping 
functions were provided to  assure photometric stability during the flight. 
The instrument operates on the principle of differential optical absorption at 253.7 nm by the 
sampled ambient air of an onboard light source. The absorption cell length is 0.71m. Ambi- 
ent air is brought into the cell through an ozone scrubber which effectively removes the ozone 
from the sampled air. The cell is illuminated by a mercury lamp where the light intensity 
i 
f 
s" 
f 6 
"> ' 
t 
OZONE 
'MONITOR 
AIR 
EJECTOR 
GAS 
RESERVOIR 
Figure 1. Balloon-borne gondola. 
2 
is measured at the end of the cell by a photodiode. The intensity of this light is converted 
to  a frequency which is stored in a counter when the level reaches a predetermined number 
of counts. This level is determined by a second detector that monitors the lamp output 
directly, establishing a reference. 
At the end of a 5-second interval, during which time the sampled air (ozone removed) has 
flushed the cell, a switch is activated t o  allow ambient air containing ozone to enter the cell 
continuously for an additional 5 seconds. At this time the attenuated light intensity due to 
ozone absorption is detected and the counter counts back down for the time determined 
by the light source monitor detector. The remaining counts are then proportional to the 
ozone. The source monitor detector removes any instability in the light source. This pro- 
cess may be described analytically by the following, where: 
N = counts proportional to the light intensity 
A = 133cm-1 (base lo),  ozone absorption coefficient at 253.7 nm (Reference 8) 
L = absorption cell length = 7 1 .O cm 
C = ozone concentration 
From Beer's Law: 
N = N e-*LC 
0 
N(up) = No, when C = 0 
N(down) = No (1 - ALC), when ALC < < I 
Then N(up) - N(down) = No ALC, which is proportional t o  the instrument output recorded 
during the flight. The instrument gain is set so that No AL = 1. Therefore, the output 
is directly proportional to  ozone concentration with corrections for the optical cell tempera- 
ture and pressure during the flight. 
Air Sampler 
Devices for air sampling at an altitude of 40 km are virtually nonexistent. Large fans become 
inefficient above 30 km and cryopumping is impractical if large air samples are required. An 
air sampler utilizing the aspirator principle was selected for this experiment because i t  could 
move substantial amounts of air near 40 km, and had been flown previously for stratospheric 
carbon14 measurements (Reference 6). The principle feature of this unit is a jet of high- 
velocity primary gas (nitrogen for this experiment) which is ejected into a mixing tube,, 
expands, and, by turbulent exchange of momentum, creates a pressure drop at the back end 
of the instrument. This causes ambient air to be drawn through the instrument. A diagram 
of the flight package is shown in figure 2 (flowmeter and manometer were utilized in an 
altitude test chamber but not in flight). The thermoconductivity-type flowmeter created 
no additional pressure drop in the system, but became insensitive to flow above a simulated 
altitude of about 35 km. Instrument pressure drop becomes critical t o  instrument perform- 
ance and subsequent data reduction since this value becomes comparable t o  the ambient pres- 
sure. For example at 30 km and 38 km the instrument pressure drop was 0.036 N/m2 and 
0.027 N/m2, respectively while the ambient atmospheric pressure at these levels is 0.12 N/m2 
3 
M 
BOM- BALLOON OZONE MONITOR N - A I R  EJECTOR NOZZLE 
R - D Y N A M I C  PRESSURE REGULATOR 
P -PRIMARY GAS 
E - EXHAUST 
T - T E F L O N  INLET TUBE 
M - DIFFERENTIAL OIL  MANOMETER 
F - FLOWMETER 
Figure 2. Schematic of balloon-borne ozone experiment. 
and 0.037 N/m2,  respectively (100 mb = 1N/m2). The pressure drop across the monitor as a 
function of altitude is shown in figure 3 and was used in the flight data reduction. This pres- 
sure drop is a function of the dynamic pressure set at the injector nozzle. The optimum dy- 
namic pressure represents a trade-off in air sampling time and flow rate. A 4-hour sampling 
time was achieved with a 9.07-kg (20-lb) dynamic pressure and a reservoir pressurized to  
1315.42 kg (2900 lbs).” 
FLIGHT RESULTS 
A 3 X 1 0+5 -cubic meter balloon was launched from Holloman Air Force Base, Albuquerque, 
New Mexico on June 27, 1974, a t  07 15 MDT with an average ascent rate of 0.27 km/min to 
38 km, and began descent at 1230 MDT. Ascent ozone data began at 16 km, when barometric 
switches activated the air sampler. A tabulation of measured ozone density as a function of 
altitude is shown in table 1. Figure 4 shows this measurement and a model compiled by Krueger 
and Minzner.? The ozone concentration remained essentially constant at the ceiling altitude 
*Pressure gage reading. 
TKrueger, A. J. and R. A. Minzner, “A Mid-Latitude Ozone Model for the 1976 U. S. Standard Atmosphere,” accepted 
for publication by J. Geophys. Res., Oceans and Atmospheres, 1976. 
4 
40 
35 
30 - 
E 
Y 
w 
- 
a 
k 
t-, a 
3 
25 
20 
100 mb = 1N/m2 
15 I- 
I I 
0.01 0.02 0.03 0.04 0.05 
PRESSURE DROP (N/m2) 
Figure 3. Pressure drop in optical ozone monitor with 
9.07-kg (20-lb) dynamic pressure a t  air ejector nozzle. 
5 
Altitude 
(km) 
17.0 
17.5 
18.0 
18.5 
19.0 
19.5 
20.0 
20.5 
21 .o 
21.5 
22.0 
22.5 
23 .O 
23.5 
24.0 
24.5 
25.0 
25.5 
26.0 
L 
Table 1 
Ozone Density versus Altitude 
Ozone Density 
(moIecule/m3 ) x 
1.12 
1.58 
2.29 
3.20 
4.08 
3.58 
3.94 
4.57 
4.59 
4.53 
4.45 
4.64 
4.64 
4.69 
4.85 
4.71 
4.90 
4.79 
4.72 
4.56 
4.37 
4.10 
Altitude 
(km) 
28.0 
28.5 
29.0 
29.5 
30.0 
30.5 
31.0 
31.5 
32.0 
32.5 
33.0 
33.5 
34.0 
34.5 
35.0 
35.5 
36.0 
36.5 
37.0 
37.5 
38.0 
Ozone Density 
(molecule/m3 ) x 
3.98 
3.82 
3.39 
3.19 
2.97 
2.80 
2.57 
2.32 
2.17 
2.01 
1.83 
1.75 
1.51 
1.46 
1.41 
1.22 
1.09 
1.09 
0.899 
0.806 
0.693 
c 
40 
30 
- 
E 
Y 
w 
3 
- 
n 
t 
5 
4 
20 
IC 
0 THIS MEASUREMENT 6-27-74 
O O MID-LATITUDE MODEL 
f 0 0 
7 
1 2 3 4 5 
OZONE DENSITY (molecule/m3) x IO-'* 
6 
Figure  4. Ozone dens i ty  versus a l t i tude .  
7 
until about 1200 MDT at which time the balloon support system was shut down. No descent 
data were obtained. 
Errors due to uncertainties in the flow and unaccountable ozone losses in the inlet system 
above an altitude of 35 km cannot be evaluated for this flight. The altitude chamber tests 
with the aspirator were not conclusive above this altitude since the flowmeter became 
insensitive. Instrument pressure drop data and extrapolation of flow data obtained in the 
altitude chamber to  40 km indicated there would be sufficient volume flow to ventilate the 
optical cell. Ozone fluxes, but not pressures expected in flight, were simulated on the 
ground and approximately 15-percent ozone losses were measured in the Teflon inlet system. 
These losses were taken into account in the flight data reduction, but could be greater at 
lower pressures because of higher diffusion rates. In either case, insufficient flow or 
additional ozone losses would cause an undermeasurement of the ambient ozone by an 
additional amount. Below about 35 km, where flow data are available, the combined 
systematic error is 13 percent. This value is derived from the square root of the sum of the 
independent errors or uncertainties in the following: electronics (signal to noise, gain, linearity, 
etc.), the measured 15 percent loss in the inlet system, ozone scrubber efficiency, leaks in the 
inlet system, absorbtion cell temperature, and pressure drop determined from the altitude 
chamber test. The pressure drop error is the most significant. Utilization of a suitable 
pressure gage would result in an improved measurement accuracy better than 10 percent. 
Comparison of the data with the reference model shows reasonably good agreement. The 
ozone distribution below the maximum is highly influenced by dynamical processes, in 
particular, the height of the tropopause. The measurement was performed near 32" N in 
June, while the model represents a seasonal average at a latitude of 45" N.  The tropopause 
was near 16.5 km at the time of the measurement, thus accounting for the lower measured 
values below the ozone maximum. 
CONCLUSION 
An in situ measurement of ozone was accomplished on a balloon platform to an altitude of 
38 km, utilizing an air ejector t o  provide the ambient air sample. The measurement is 
absolute since it is based on the attenuation of light by ozone in spectral region where the 
absorption coefficient is well established. The flight resulted in a vertical ozone distribution 
which is comparable with levels of ozone measured by other techniques. Errors in the data, 
mainly near floating altitude, are due to  uncertainties in providing adequate flow and 
unaccountable losses of ozone in the inlet system. These uncertainties could be removed by 
additional altitude chamber tests and the use of a more sensitive flow measurement. a 
Goddard Space Flight Center 
National Aeronautics and Space Administration 
Greenbelt, Maryland June 1976 
8 
REFERENCES 
1. Komhyr, W. A. and D. R. Sticksel, Ozone Observations 1962-1 966, ESSA Technical 
Report, IER SI-IASI, August 1967. 
2. Regener, V. H., “Measurement of Atmospheric Ozone with the Chemiluminescent 
Method,” J. Geoplzys. Res., 69, (1 8), 1964, pp. 3775-3800. 
3. Herring, W. S., “Comparison of Chemiluminescent and Electrochemical Ozonesonde 
Observations,” f. Geophys. Res., 70, (22), 1965, pp. 5483-5490. 
4. Krueger, A. J., “The Mean Ozone Distribution from Several Series of Rocket Soundings 
to  52 kin at Latitudes from 58”s to  64”N,” Pure Appl .  Geophys., 106-108, 1973, 
pp. 1272-1 280. 
5.  Hilsenrath, E., “Ozone Measurements in the Mesosphere and Stratosphere During Two 
Significant Geophysical Events,”J. Atm.  Sci., 28,  (2), 1971, pp. 295-297. 
6. Ashenfelter, T. E., J. Gray, Jr., R. E. Sowl, M. Svendsen, and K. K. Telegadas, “A 
Lightweight Molecular Sieve Sampler for Measuring Stratospheric Carbon-1 4,” J. 
Geophys. Res., 77, (3), 1972, pp. 412-419. 
7. Bowman, L. D. and R. F. Horak, “A Continuous Ultraviolet Absorption Ozone 
Photometer,’’ ISA, AID 72430, 1972, pp. 103-108. 
8. Inn, E. C. and T. Tanaka, “Ozone Absorption Coefficients in the Visible and Ultraviolet 
Regions,” Ozone Clieinistry and Technology, No. 21 of Advances in Chemical 
Series, American Chemical Society Publishers, Washington, D.C., 1959. 
NASA-Langley, 1976 9 
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A balloon ozone measurement utilizing an optical absorption cell and an ejector air sampler

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