Vertical distribution profiles of N2O and CH4 have been measured from Hyderabad, India using a balloon-borne cryogenic air sampler. The samples have been analyzed using gas chromatographic techniques. Results for two balloon flights made in 1987 and 1990 show effects of tropical characteristics like higher tropopause and upwelling motion due to Hadley circulation. These profiles also exhibit perturbations around 25 km height, which are likely to be due to dynamical effects. A comparison with the SAMS data show that the SAMS values for both these gases are higher by a factor of about 1.5 to 2 around 30 km height

Borchers, R.

Fabian, Peter

Lal, Shyam

Subbaraya, B. H.

English

NASA Technical Reports Server

N95-11099
VERTICAL DISTRIBUTION OF CH 4 and N20 OVER
THE TROPICAL SITE HYDERABAD
Shyam Lal and B.H. Subbaraya
Physical Research Laboratory
Ahmedabad 380 009, India
P. Fabian* and R. Borchers
Max Planck Institute for Aeronomy
D-3411, Katlenburg-Lindau-3, Germany
ABSTRACT
Vertical distribution profiles of N20 and
CH 4 have been measured from Hyderabad, India
uslng balloon borne cryogenic air sampler. The
samples have been analysed using gas
chromatographic techniques. Results for two
balloon flights made in 1987 and 1990 show
effects of tropical characteristics like higher
tropopause and upwelling motion due to Hadley
circulation. These profiles also exhibit
perturbations around 25 km height, which are
likely to be due to dynamical effects. A
comparison with the SAMS data show that the SAMS
values for both these gases are higher by a
factor of about 1.5 to 2 around 30 km height.
i. INTRODUCTION
Nitrous oxide and methane are the two
important trace gases which have biogenic
sources. Both these gases play important role in
atmospheric chemistry and radiation processes,
particularly relating to ozone and global
warming. Methane also reacts with OH radical
which is the controlling radical for entry into
the stratosphere for many trace gases. These
gases have also been identified to play
significant role in global warming through the
absorption of the outgoing earth's infrared
radiation (Ramanathan et al., 1985; IPCC, 1990).
It has been found that methane and nitrous oxide
contribute about 21% to the total change in
radiative forcing from 1980 to 1990 (IPCC, 1990).
Abundances of these gases have been increasing in
the earth's atmosphere. While, nitrous oxide is
found to be increasing at a rate of about 0.2-
0.3% per year (Weiss, 1981; Rasmussen and Khalil,
1986; Robinson, 1988; Prinn et al., 1990; Sheel
et al., 1990; WMO, 1991), methane is increasing
at a rate of about 0.8-1% per year (Blake and
Rowland, 1988; WMO, 1992). Tropical regions
contribute about 50% of the total global sources
*Presently at :
Lehrstuhl fur Bioklimatologie und Immissions-
forschung, der Universitat Munchen
Hohenbachernstr.22,
W-8050 Freising Weihenstephan, Germany
of both these gases (WMO, 1985). Tropical forests
and oceans are the major sources of N20. The
North-West Indian ocean (15-25°N) represents one
of the most significant marine source of N20 (Law
and Owens, 1990). Major sources of methane are
natural wetlands, rice paddies and enteric
fermentation. These too have large spread in the
measurements (IPCC, 1990).
The vertical distribution data, which are
important for modelling the chemistry of the
troposphere and stratosphere are also limited
particularly in the tropical region. There have
been a series of measurements from the mid-
latitude region using balloonborne sampling
technique (Ehhalt, 1980; Fabian et al., 1981;
Schmidt et al., 1984; Lal et al., 1989a).
However, only few measurements of these gases
have been made in the tropical regions (Ehhalt
and Toennissen, 1979; Lal et al., 1989b; Borchers
et al., 1989).
A programme has been undertaken jointly by
Physical Research Laboratory (PRL), Ahmedabad,
India and Max Planck Institute for Aeronomie
(MPAE), Lindau, Germany to study the vertical
distribution of trace gases from Hyderabad
(17.5°N). This paper presents the results of two
balloon flights conducted from this site on March
27, 1987 and April 9, 1990.
2. EXPERIMENTAL DETAILS
Three balloon flights carrying a composite
payload consisting of a cryogenic air sampler of
MPAE, Lindau and a suntracking multichannel
photometer of PRL, Ahmedabad were launched from
the tropical site, Hyderabad (17.5°N). The
details of the balloon flights are given in Table
I. The neon cooled cryogenic air sampler
collected 15 samples during each flight in the
height range of 10 to 35 km. The descent of the
balloon was controlled using an apex valve and
some of the samples were collected during this
part of the trajectory also. The first flight in
1985 was a test flight and adequate amount of
samples could not be collected during this
flight. Air samples of about i0 litre at STP
were collected with sampling times ranging from 1
823
https://ntrs.nasa.gov/search.jsp?R=19950004686 2020-06-16T11:29:05+00:00Z
Table 1 : Details of balloon flights from Hyderabad, India for trace gas studies
Launch Date Launch Time Cut-off Time Ceiling Altitude Experiments
Hrs. (IST) Hrs. (IST) (km.)
27.03.1985 0608 1150 35.3 Cryogenic air
sampler and
multichannel
photometer
-do-26.03.1987 0545 1508 34.5
09.04.1990 0536 1350 33.7 -do-
minute at Ii km to 60 minutes at 34 km during the
last two flights. Further, details of the
cryogenic air sampler and sampling procedure are
given in Fabian (1981).
The collected air samples have been
analysed at the MPAE, Lindau using gas
chromatographic and coupled mass-spectrometric
techniques for N O and CH alongwith many other
trace gases. Nitrous oxid_ was analysed using a
gas chromatograph coupled with a quadrupole mass-
spectrometer while methane was analysed using a
gas chromatograph with a Flame Ionization
Detector (FID). The analyses were done against a
laboratory standard which was calibrated using
known mixtures of high purity gases. The
repeatability of the analyses is better than 2%.
However, the errors in calculating absolute
mixing ratios which arise mainly due to
calibration mixtures are of the order of 5%.
3. RESULTS
The profiles of CH 4 and N O obtained from
balloon flights in 1987 and 19_0 are shown in
Figures 1 and 2 respectively. Both the gases
show almost uniform mixing ratio in the altitude
region below 20 km. Above this height the mixing
ratios start decreasing. This feature is
concurrent with the high tropical tropopause.
Also, there is no appreciable difference in the
tropospheric values of these gases for the two
flights.
In the stratosphere, mixing ratio of N20
decreases much faster than CH 4 due to higher loss
rate compared to CH 4. The variability observed
in the two sets of profiles for the two gases is
identical. The 1987 profiles of CH and N20 show4
sudden change around 25 km but thls feature is
not observed in the profiles of 1990. The 1987
flight shows an increasing trend in the mixing
ratios of the two gases above 25 km followed a
slow decrease. However, there is a sharp fall
beyond 30 km but there is only a single data
point. Contrary to this, the 1990 flight shows a
steady decreasing trend throughout except for a
small decrease in the height range of 22 to 25
km. This indicates that the region around 25 km
height has some special features. Wind data for
the two flight dates do not show any appreciable
change around 25 km altitude eventhough the wind
profiles do differ in the tropospheric region
(Fig. 3a,b). Similar abnormality in several
504
CH,
40- o
o x
o
30- =
Z0-
o D Hyderabad, March 27, 1987
10- _ _ _ Hyderabad. April 9, 1990
o o o SAilS Average, March (20_)
_ _ avaos SL-a, (28"N)
---- Southern France (44"N), kverl_e
l
Mixing Ratio (ppmv)
o
s
o
A
_ x a
_ sa
L _ a
t_
A',
/
\
i
Fig. i. Vertical distribution of CHA measu-
red over Hyderabad during 1987 and
1990 and a comparison with other
measurements.
longlived trace gases has been seen in the
profiles measured from Southern France (44°N) but
at a lower height around 22 km (Lal et al.,
1989a,b); Borchers et al., 1989). The
perturbation observed in these profiles appears
to be due to dynamical effects as there cannot be
sudden change in the photo-dissociation rates of
these gases. Spectroscopic measurements of CH 4
and N20 during a shuttle mission from April 30 to
May 6, 1985 consistently showed a 'fold' around
30 km altitude (Gunson et al., 1990).
4. COMPARISON WITH OTHER MEASUREMENTS
Figures 1 and 2 also show a comparison of
the Hyderabad profiles with the average profile
based on measurements made from Southern France
(44°N) using similar sampling and analysis
techniques. Measurements made with spaceborne
techniques like Stratospheric and Mesospheric
824
50
N_0
40-
_,_30 -
Z0-
_.0-
x
o
o x
o
_ o
a _ _ D
_ A
a x zs
' no
\.%
[] o D Hyderabad, March 27, 1987 _
a _ Hyderabad, April 9, 1990
o o o S/t.MS Aver_ge_ March (80*N)
× _ x ATMOS SL-3 (28"N) ° i
--- Southern. France (44 N), Average
,6o z_o 3_o " '
Mixing Ratio (ppbv)
Fig. 2. Vertical distribution of N 0 measu-
red over Hyderabad during _987 and
1990 and a comparison with other
measurements.
Sounder (SAMS) and the Atmospheric Trace Molecule
Spectroscopy (ATMOS) flown onboard Spacelab-3
(SL-3) mission given by Taylor et al. (1989) and
Gunson et al. (1990) respectively, are also
presented in these diagrams. Comparison with the
mean mid-latitude data show very clearly the
effect of upwelling in the Hyderabad profiles.
The Hyderabad profiles show decrease in the
mixing ratio only above 20 km while the mid-
latitude profile shows decrease above 15 km
itself. However, above about 28 km the Hyderabad
data fall within the range of the mid-latitude
data. This sharp gradient above 25 km in the
Hyderabad profiles appear to be due to intense
solar radiation prevailing in the tropical region
compared to the mid-latitude region and
consequent increased photodissociation.
Average data for 20°N for the month of
March based on the SAMS data for both the gases
are presented in Figures 1 and 2. In case of
CH., the SAMS values are higher than the
Hy_erabad values at all altitudes except three
data points of the 1987 flight in the 26 to 30 km
altitude. The increase is by a factor of about
1.5. Similarly, N 0 values derived from the
SAMS results are h_gher but the difference
increases with height. Around 30 km, the SAMS
values are higher by a factor of about 2.
The ATMOS experiment data for CH is within
the average values of the mean m_d-latitude
profiles. However, the N 0 values are almost
2
representing the Southern France data.
5. SUMMARY
The measurements of CH 4 and N20 made from
Hyderabad show the effect of strong upwelling
motion. Over Hyderabad, the constant mixing
ratio region extends upto almost 20 km height as
against 15 km observed in the mid-latitude
region. There is a sharper decrease in the
mixing ratios of these gases above 25 km
compared to the mid-latitude profiles, probably,
due to higher amount of solar radiation reaching
at these heights in the tropics.
The SAMS data show higher mixing ratio of
these gases compared to the Hyderabad profiles
while the ATMOS experiment data for both the
gases for 28°N almost represent the mid-latitude
profiles. This aspect needs more in-situ,
preferably simultaneous, observations, to
delineate the biases.
ACKNOWLEDGEMENTS
These balloon flights were conducted
jointly by PRL, Ahmedabad and MPAE, Lindau,
Germany under the ISRO (India) and the DLR
(Germany) collaborative programme. We would
like to thank the members of two organizations
for their help in coordinating and executing
this programme. Thanks are also due to
Prof.S.V. Damle, Mr.R.T. Redkar and other team
members of TIFR Balloon Facility, Hyderabad and
to the members of PRL, MPAE and DLR who helped
in conducting these experiments. We also
acknowledge the support of Mr. P. Rajaratnam of
ISRO Headquarters, Bangalore for successfully
managing these campaigns.
REFERENCES
Blake, D.R. and F.S. Rowland, 1988: Continuing
worldwide increase in tropospheric
methane, 1978 to 1987, Science, 239, 129.
Borchers, R., P. Fabian, O.N. Singh, S. Lal and
B.H. Subbaraya, 1989: The vertical
distribution of source gases at tropical
latitudes, In "Ozone in the Atmosphere",
Proceedings of the Quadrennial Ozone
Symposium, 1988 and Tropospheric Ozone
Workshop, Eds. R.D. Bojkov and P. Fabian,
A. Deepak Publishing, USA., 290.
Ehhalt, D.H., 1980: In-situ observations, Phil.
Trans. R. Soc., Lond., A.296., 175.
Ehhalt, D.H. and A. Toennissen, 1980: Hydrogen
and carbon compounds in the stratosphere,
In "Proceedings of the NATO Advanced Stud_
Institute on Atmospheric Ozone : Its
variations and Human Influences, Rep.
No.FAA-EE-80-20, USA., Ed. C. Aikin, 129.
Fabian, P., 1981: Atmospheric sampling, Adv.
Space Res., l, 17.
Fabian, P., R. Borchers, G. Flentje, W.A.
Mathews, W. Seller, H. Giehl, K. Bunse, F.
Muller, U. Schmidt, A. Volz, A. Khedim and
F.J. Johnen, 1981: The vertical
distribution of stable trace gases at mid-
latitudes, J. Geophys. Res., 86, 5179.
825
4O
3O
v
w
r_
_ 2O
I0
1 i i
J,
,i'
"-(:
HYDERABAD
26 MARCH,87
Merldionol
Zonol
f,.
i i [
-30 -20 I0 0
I I 1
I0 20 30
WIND SPEED (rnls)
50 ¸.
40-
---_30-
OJ
_-_ 2O-
.<
I0-
Hyderabad
April 8,1990
.... Zonal
-- Meridional
?
0-
-40 o 23
Wind Speed (m/see)
Fig. 3a & b. Wind profiles measured during the flight periods.
Gunson, M.R., C.B. Farmer, R.H. Norton, R.
Zander, C.P. Rinsland, J.H. Shaw and B.C.
Gao, 1990: Measurements of CH 4, N_O and 03
in the middle atmosphere by the a_ospheric
trace molecule spectroscopy experiment on
spacelab 3, J. Geophys. Res., 95, 13867.
I.P.C.C., 1990: Climate Change : "Th__e
Inter_overnmental Panel on Climate Change -
Scientific Assessment, Eds. J.T. Houghton,
G.J. Jenkins and J.T. Ephraums, Cambridge
Univ. Press., Cambridge, USA.
Lal, S., R. Borchers, P. Fabian and B.C. Krueger,
1989a: The vertical distribution of CH ,
and CFC-II in the middleN O, CFC-12
a_osphere at mid-latitudes, J. Atmos.
Terr. Phys., 51, 81.
Lal, S., B.H. Subbaraya, S. Venkataramani, P.
Fabian and R. Borchers, 1989b: Minor
constituents in the tropical atmosphere,
Ind. J. Radio & Space Physics, 18, 171.
Law, C.S. and N.J.P. Owens, 1990: Significant
flux of atmospheric nitrous oxide from the
north-west Indian ocean, Nature, 346, 826.
Prinn, R., D. Cunnold, R. Rasmussen, P. Simmonds,
F. Alyes, A. Crawford, P. Fraser and R.
Rosen, 1990: Atmospheric emissions and
trends of nitrous oxide deduced from i0
years of ALE-GAGE data, J. Geophys Res.,
95, 18369.
Ramanathan, V., R.J. Cicerone, H.B. Singh and
J.T. Kiehl (1985) : Trace gas trends and
their potential role in climate change, J___.
Geophys. Res., 90, 5547.
Rasmussen, R.A. and M.A.K. Khalil, 1986:
Atmospheric trace gases : Trends and
distributions over the last decade,
Science, 232, 1623.
Scheel, H., E. Brunke and W. Seiler, 1990: Trace
gas measurements at the monitoring
station, Cape Point, South Africa, between
1978 and 1988, J. Atmos. Chem., ii, 197.
Schmidt, U., A. Khedim, D. Knapska, G. Kulessa
and F.J. Johnen, 1984: Stratospheric trace
gas distributions observed in different
season, Adv. Space Res., 4, 131.
Taylor, F.W., A. Dudhia and C.D. Rodgers, 1987:
Proposed reference models for nitrous
oxide and methane in the middle
atmosphere, Adv. Space Res., 7(9__!), 49.
Weiss, R.F., 1991: The temporal and spatial
distribution of tropospheric nitrous
oxide, J. Geophys. Res., 86, 7185.
W.M.O., 1985: "Atmospheric Ozone 1985", World
Meteorological Organization, Rep. No. 16,
Vol. 1,
W.M.O., 1991: "Scientific Assessment of Ozone
Depletion : 1991, World Meteorological
Organization, Rep. No. 25.
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Vertical distribution of CH4 and N2O over the tropical site Hyderabad

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