Preliminary calculations suggest that heterogeneous reactions are important in calculating the impact on ozone from emissions of trace gases from aircraft fleets. In this study, three heterogeneous chemical processes that occur on background sulfuric acid aerosols are included and their effects on O3, NO(x), Cl(x), HCl, N2O5, ClONO2 are calculated

Kinnison, Douglas E.

Wuebbles, Donald J.

English

NASA Technical Reports Server

N95- 10666
IMPACT OF SUPERSONIC AND SUBSONIC AIRCRAFT ON OZONE: INCLUDING HETEROGENEOUS
CHEMICAL REACTION MECHANISMS.
Douglas E. Kinnison and Donald J. Wuebbles
Lawrence Livermore National Laboratory
Livermore CA 94550, USA
ABSTRACT
Preliminary calculations suggest that heterogeneous
reactions are important in calculating the impact on ozone
from emissions of trace gases from aircraft fleets. In this
study, three heterogeneous chemical processes that occur on
background sulfuric acid aerosols are included and their
effects on 03, NOj t , C11, IICI, N205, CIONO 2 are calculated.
INTRODUCTION
The aircraft industry is showing interest in the
development of supersonic, lligh Speed Civil Transports
(HSCT's) for intercontinental passenger flights. The purpose
of this study is to extend recent research (Johnston et al.,
1989; Weisenstein et al., 1991; Kinnison and Wuebbles,
1991; and Jackman et al., 1991) examining global
environmental effects from potential future emissions of
commercial aircraft fleets. In addition to the gas-phase
reaction mechanism believed to be important in the
troposphere and stratosphere, three heterogeneous chemical
processes that occur on and within the bulk of sulfuric acid
aerosols are investigated. In this study the LLNL two-
dimensional zonally averaged chemical-radiative-transport
model of the troposphere and stratosphere is used to
investigate the effects of NO x emissions from future fleets of
both subsonic and supersonic aircraft on ozone and other
trace gas distributions. Recent uses of this model include
those of Johnston et al., 1989 and Wuebbles et al, 1992. For
a general description of the LLNL 2-D model, see Kinnison et
at., 1992.
ItFTEROGENEOUS REACTIONS
In this study, we added the following reactions to the
LLNL 2-D model chemistry package:
N205 (g) [+1120 in aerosol] --> 2 IlNO 3 (g) (1)
C1ONO 2 (g) [+1120 in aerosol] --> IINO 3 (g) + 110(21 (g) (2)
Since a complete treatment of these reactions would require a
sophisticated aerosol microphysical model, which currently
has both the'dCretical and practical limitation, we treated these
reactions using the following relationship to calculate the
two rate coustants for the above cases.
for this study. The reaction probability per collision (30 is
based on laboratory measurements (WMO/UNEP, 1992). For
N20 5 on sulfuric acid aerosols the reaction probability (Yt)
is set to 0.1 and does not have a temperature dependence. The
reaction probability for C1ONO 2 on sulfuric acid aerosols
does have a temperature dependent expression:
y2=0.006exp(-0.15(T-200)).
In addition, Burley and Johnston (1992), have proposed
an additional heterogeneous chemical mechanism. This
mechanism has the net effect of converting IICI into CINO. A
brief description of the major points about this mechanism
are described below. For a more complete description of the
modeling approach use in this study, see Connell et al.,
1992.
*Nitrosyl sulfuric acid (NSA) -- NOHSO 4 -- has been observed
as a solid crystalline precipitate in the stratospheric
sulfuric acid aerosol
*NSA can be present in sulfuric acid solutions where the
I!2SO 4 weight per cent is greater than 60 % at typical
stratospheric temperatures, either as an ionic solid --
NO+IISO4" -- or as Ii2ONO + and HSO,( in solution
*Potential NSA formation reactions (13urley and Johnston,
1992) on sulfuric aerosols include:
NO + NO2 + 2 II2SO4 = 2 NOitSO4 + 1120
NO + IINO 3 + i 12SO4 = NOI ISO4 + NO.2 + 1120
IIONO + 112SO 4 = NOHSO 4 + i!20
*ItCI reacts with NSA to form CINO:
ilCI + NOHSO 4 = CINO + H2SO 4
*The CINO produced is readily photolyzed to form CI:
CINO + hv = CI + NO
*The overall process is the acid-catalyzed conversion of the
chlorine reservoir species IIC1 to active atomic CI
EMISSION SCENARIO FOR 2015 AIRCRAFT
FLEET
K = (V)(T)(Surface Area I)cnsity)
Surface area density (cm2/cm 3) for the reference atmosphere is
based on analysis of Sage II data by Poole, Thomason, and
Yue (WMO/UNEP, 1992). This distribution is representative
of an atmosphere that has not been influenced by a major
volcanic eruption. The surface area density distribution has
altitude (12-32 km), latitude (90N-90S), and temporal
resolution. The effective collision velocity (V) is 5200 cm/s
Emission scenarios for this study are taken from a recent
investigation conducted by the NASA Iligh Speed Research
Program (Prather et al, 1992). In these scenarios both
subsonic and supersonic aircraft fleets are represented for the
year 2015. The trace gas emissions for the 2015 subsonic
scenario are based on the Boeing B6 scenario. The subsonic
emission scenario was divided into two regions, flights under
400 miles or sbort range, and flights greater than 400 miles
or long range. The total amount of fuel consumed is 20 x 109
kg/year and 150 x 109 kg/year for short and long range
318
https://ntrs.nasa.gov/search.jsp?R=19950004254 2020-06-16T11:25:58+00:00Z
flights respectively. The subsonic emission index for NO x is
20.'/ g/kg fuel consumed. The altitude of injection for short
range flight is between 6.1 and 9.1 km and between 9.1 and
12.2 km for long range flights. For this study only the Mach
2.4 (16.8-19.8 km) airframc was considered. The total
amount of fuel consumed for the supersonic scenario is kept
constant at 70 x 109 kg/year, which represents
approximately 500 aircraft. The supersonic emission index
for NOx is 15g/kg fuel consumed. For the above prototype,
fuel use during take off, climb, and descent is ignored. In both
the subsonic and supersonic emission scenarios, the NOx
emitted is 90% NO and 10% NO 2 on a molecular basis.
60
5O
_ 4o
< 20
10
- 400.-
0 , , i ........ _--'---,
-90 -60 -30 EQ 30 60 90
LATITUDE
Figure 1: Rate of reaction of IICI + O11 = CI + 1120 (molec.
cm 3 s l) for an ambient 2015 atmosphere that includes N205
and CIONO 2 reactions on sulfuric acid aerosols, summer
solstice.
6O
5O
UJ 4O
a
I- 3O
I--
_._1
< 2O
10
• ' I ' ' I ' ' I ' ' 1 ' ' I ' '
0 I , I , , I , , I , , I , , I , ,
-90 -60 -30 EQ 30 60
LATITUDE
9O
Figure 2: Rate of reaction of IICI + NSA = CINO (g) +
ll2SO 4 (molec. cm "3 s"l) for an ambient 2015 atmosphere that
includes NSA, summer solstice. Contour intervals are: 200,
400. 600... with a maximum of 1200.
RESUI,TS
In figure 1, the IICI and Oil rate of reaction is shown for
the ambient 2015 heterogeneous atmosphere that includes
the reactions of N205 and CIONO 2 on sulfuric acid aerosols.
Figures 2 indicates the importance of the NSA mechanisms
for converting IICI to reactive chlorine in the lower
stratosphere. Including the NSA mechanism reduces HCI by
up to 10-20 percent in the lower stratosphere, increasing the
CIONO2/ilCI ratio by 20-30 %; CI s (CI + C10) and NO x (NO +
NO2) change by +50 to +200 % and -4 to +g % respectively
(see Connell et al., 1992 for more details on the impact of
NSA on trace gas distributions). As NO x is increased from the
proposed aircraft scenario, the NSA concentration will
increase which increases the NSA + IICI reaction rate, at high
latitudes, Northern Hemisphere, from 1200 to 1800
molecules cm "3 s"1. The iiCI concentration decreases by
another 15 percent in this region.
Table I: Percent change in CIONO2/HC1, CI x, and NO x from
the Mach 2.4 aircraft fleet emission of NO x, at midlatitudes,
in the Northern Hemisphere, Jul_t 15.
Chemistry Set CIONO2/HC1 CI x NO t
Gas-phase -20 to -30 -50 to -60 +80
Heterogeneous -4 to -8 -40 +60
Her. with NSA +20 to +40 -20 +50
In figure 3, the percent change in column and local ozone
is plotted for gas-phase, heterogeneous (N205 and CIONO 2
reactions) and heterogeneous (N205 and CIONO 2 reactions)
with the NSA mechanism. Without the heterogeneous
chemical reactions, the NO x emissions decrease global
ammal-average column ozone by -1.4 %. This decrease is due
to the 80 % increase in NOx which increases the rate of odd
oxygen loss from the NO x catalytic cycles (table 1).
Including both the N20 5 and CIONO 2 heterogeneous
reactions decreases the effect on ozone of the Mach 2.4
scenario (figures 3b and 3c). The percent global annual-
average column ozone change is -0.21 %. With the
heterogeneous reactions present, the odd oxygen loss from
the NO x catalytic cycles are reduced and the CI x catalytic
cycles are increased. As the emitted NOx reacts with the
enhanced CI x in the heterogeneous atmosphere, the local
excess NOx is reduced, minimizing the fleets impact on
ozone. When the NSA mechanism is included, the change in
global annual-average column ozone is -0.15 %. The net
effect of the aircraft NO x emissions is to increase the
CIONO2/HCI ratio, but at least for this Math 2.4 scenario, did
not change ozone concentrations dramatically (compare
figures 3c and 3e).
Derived local ozone increases in the troposphere when the
heterogeneous reactions are present. This is not observed in
the gas-phase case (compare figures 3b with 3d). Since the
heterogeneous reactions decrease NO x relative to the gas-
phase only mechanism, additional input of NOx is very
efficient in producing ozone via the Cll4-NOx-smog
reactions.
When emissions of the proposed subsonic fleet are
included with the Mach 2.4 supersonic fleet, maximum local
ozone changes in the troposphere are greater than 10 % for
the heterogeneous case without NSA chemistry (figure 4).
Approximately 3 percent (see figure 3d) of this change is
from supersonic emissions and the rest is due to subsonic
emissions. Both the heterogeneous with and without NSA
showed similar increases in tropospheric ozone. The global
319
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Figure 3: Percent change in ozone relative to an ambient atmosphere withoul aircraft for: a) column ozone, gas-phase reaction
set; b) local ozone, gas-phase, July 15; c) column ozone, heterogeneous (it.. N205 and CIONO 2 reactions); d) lo_al o.'.onc,
heterogeneous, July 15; e)column ozone, heterogeneous with NSA; f) local ozone, heterogeneous with NSA , July 15. q2_c_t, ar_: n,,
subsonic emissions included in these cases.
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REFERENCES
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CONCI,USIONS
1) The rate ofOll + NSA is comparable to Oll+ 11CI in the
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2_ With the gas-phase only chemistry mechanism, relatively
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3) Including N20 5 and CIONO 2 reactions on sulfuric acid
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4) Including NSA chemistry with the N20 5 and CIONO 2
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6) When subsonic emissions are included with the proposed
IISCT fleet, large positive changes in tropospheric
oT_one are derived (Figure 4).
ACKNOWI,EDGMENTS
The authors would like to thank Chi Tang for her
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stt_dy. This work was performed under the auspices of the U.S.
Department of Energy by the l.awrence Livermore National
I.aboratory under contract No. W-7405-Eng-48 aud wa_
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Impact of supersonic and subsonic aircraft on ozone: Including heterogeneous chemical reaction mechanisms

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