Atmospheric perturbations caused by the emission of nitrogen oxides from a projected fleet of stratospheric aircraft are studied with a two dimensional chemistry, transport model. Photochemistry of the lower stratosphere, the region where these aircraft may fly, is now known to be influenced by heterogeneous reactions involving sulfuric acid aerosols. This study examines the sensitivity of the atmospheric effects of aircraft to heterogeneous reactions. Information of background aerosols based on the SAGE 2 measurements have been used in the parameterization of the heterogeneous conversion rates. It is found that heterogeneous reactions make the lower stratospheric ozone less sensitive to perturbations in the odd nitrogen level. The calculated reduction in global ozone due to NO(x) injection from a fleet of Mach 2.4 aircraft is 1.28 percent if gas phase reactions only are considered in the model, and 0.06 percent if heterogeneous reactions are included

Boughner, R. E.

Callis, L. B.

Lambeth, J. D.

Natarajan, M.

English

NASA Technical Reports Server

N95-10678
IMPACT OF STRATOSPHERIC AIRCRAFT EMISSIONS ON
OZONE: A TWO DIMENSIONAL MODEL STUDY
M. Natarajan 1, L. B. CaUis 2, R. E. Boughner 2, and J. D. Lambeth 1
1 Science Applications International Corporation
Hampton, Virginia 23666, USA.
2 Atmospheric Sciences Division, NASA Langley Research Center
Hampton, Virginia 23681, USA.
ABSTRACT
Atmospheric perturbations caused by the emission of
nitrogen oxides from a projected fleet of stratospheric air-
craft are studied with a two dimensional chemistry, trans-
port model. Photochemistry of the lower stratosphere, the
region where these aircraft may fly, is now known to be in-
fluenced by heterogeneous reactions involving sulfuric acid
aerosols. This study examines the sensitivity of the atmo-
spheric effects of aircraft to heterogeneous reactions. In-
formation on background aerosols based on the SAGE II
measurements have been used in the parameterization of
the heterogeneous conversion rates. It is found that het-
erogeneous reactions make the lower stratospheric ozone
less sensitive to perturbations in the odd nitrogen level.
The calculated reduction in global ozone due to NOx injec-
tion from a fleet of Mach 2.4 aircraft is 1.28% if gas phase
reactions only are considered in the model, and 0.06% if
heterogeneous reactions are included.
1. INTRODUCTION
Recent interest in the development of high speed civil
transport aircraft has revived the concerns regarding the
effects of aircraft exhaust gases on atmospheric ozone. Re-
sults from early model calculations of the perturbation due
to a projected fleet of aircraft have been documented by
the High Speed Research Program (NASA RP-1272, 1992).
Ambient atmosphere with source gas mixing ratios pro-
jected for the year 2015 has been used in these studies as
the baseline case. Aircraft fuel usage scenario as a function
of latitude, and NOx emission index in the range 5 to 45
gins of NOx /kg of fuel have been adopted. Model results
for NOx injection at three different altitudes (based on the
Mach number of the aircraft) have been reported. The
calculated reductions in global ozone for different models
ranged from 0.72% to 2.1%, for Mach 2.4 aircraft with an
emission index of 15 for NOx. All these models consid-
ered only gas phase reactions. The identification of the
heterogeneous reactions on polar stratospheric clouds as
a necessary component of the mechanism leading to the
springtime ozone loss in the antarctic region, and the sub-
sequent advances in laboratory studies of possible hetero-
geneous reactions on sulfuric acid droplets have revolution-
ized our understanding of the lower stratospheric photo-
chemistry. Reaction probability for the reaction,
N20s + H=O _ HNOs + HNOs (i)
involving sulfuric acid aerosols is believed to be high. Re-
cent work by Hanson and Ravishankara (1991) suggests
that the probability of the reaction,
C1ONO2 + H20 --* HOC1 + HNOs (2)
on sulfuric acid aerosols is a function of the acidity of the
aerosol, and this reaction could be important under colder
temperatures and/or larger aerosol loading. The conver-
sion of reactive odd nitrogen into HNOs will also shift the
partitioning of odd chlorine species, and recent measure-
ment campaigns have reported data on C10 that are con-
sistent with this theory. It is therefore essential that model
studies of the aircraft effects should take into account the
heterogeneous reactions on sulfuric acid aerosols. This pa-
per describes one such study. Weisenstein et al. (1991)
have also reported a similar study of the impact of reac-
tion (1) on ozone response to aircraft emissions.
2. MODEL DESCRIPTION
The basic tool used in this study is a two dimensional
chemistry, transport model developed on a potential tem-
perature - latitude grid. This 'model extends from the
ground to 2700 K surface. Main features of the model
have been described by Callis et al.(1991). We have used
NMC temperature data and ozone climatology in a ra-
diative transfer code to calculate the monthly averaged
diabatic heating rates. The advective fields are derived
from these heating rates. Tropospheric fields have been
calculated from heating rates based on FGGE data. We
have adopted the horizontal mixing coefficients from Yang
et al. (1990). The following chemical species are trans-
ported in the model: Ox, NOy, HNOs, Cly, CH4, H20,
CO, N_O, CC14, CHsC1, CHsCCls, CFCls, CF2C12, HC1,
and CHF_C1. SAGE II H20 data have been used in the
troposphere. Photochemical and kinetic data are adopted
from NASA Evaluation JPL 90-1.
367
https://ntrs.nasa.gov/search.jsp?R=19950004266 2020-06-16T11:24:55+00:00Z
40
3O
9
I0
_ ---::-.....::-::::.):.::------::-_i_i_
... -.... ... .... ..,,_.---.0 4 I I
-90 -80 -30 0 30 80 90 1 2 3 4 5 8 7 8 9 10 11 12
Latitude Month
Figure 1: Percent change in total odd nitrogen in July due to
NOx injection from Mech 2.4 aircraft.
Figure 3: Same as figure 2, for Model H.
For the model with heterogeneous reactions, the dis-
tribution of the background aerosol surface area density is
based on the information derived from the SAGE II mea-
surements for 1989. 71, the reaction probability for reac-
tion (1) is 0.I, and ?_ iscomputed as a function of the acid-
ity of the aerosol (Hanson and Ravishankara, 1991). Het-
erogeneous reations involvingpolarstratospheric clouds
have not been included. The boundary values for the
source gases are taken from NASA RP-1272, and these
are the recommended data to simulate the conditions in
the year 2015. The baseline atmosphere in this study in-
cludes the NO= injection from the subsonic aircraft flying
in the altitude range 6.1-12.2 kin. The fuel usage for the
subsonic aircraft is 170 x 109 kg/year and that for the
supersonic fleet is70 x 109 kg/year. The latitudinal distri-
bution of the fuel use is taken from NASA RP-1272. We
have considered only the effects of NOx emission in this
study.
.of. ,;,,.;,:p,i, ,_:._:,, _
::::::::::::::::::::::::::....?J____.
=====================================
=======================.....-_::_-:_:
1 2 3 4 5 6 7 8 9 10 11 12
Month
Figure 2: Percent change in totalozone for Model G (gas phase
chemistry only) due to NOx injection from Mech 2.4 aircraft.
3. RESULTS AND DISCUSSION
In the following discussion, 'Model G' denotes the case
with only gas phase chemistry, and 'Model H' includes, in
addition, the heterogeneous reactions on the background
aerosols. NO= injection from Mach 2.4 aircraft occurs in
the altitude range 16.8-19.8 kin. The percent change in the
total edd nitrogen due to this injection for July is shown
in Figure i. The maximum change is about 80%, and this
occurs between 30 ° N and 60° N. Total ozone perturbation
caused by this increase in NO r isshown in Figures 2 and 3
for the model G and H respectively. Model G yields ozone
reductions at all latitude regions. Maximum reduction of
3.2% occurs in the northern high latitudes. The response
of the atmospheric ozone to NOx injection in the presence
of heterogeneous reactions isdramatically different. In this
case, most regions in the northern hemisphere show small
increases in total ozone. In the high latitude southern
hemisphere ozone reductions of 0.8% are seen. It should
be noted that the aircraft fuel usage and hence the NO=
input are weighted heavily towards the northern latitudes.
The vertical distribution of the ozone perturbation in July
are shown in Figures 4 and 5. When only gas phase reac-
_,:..:_--.... ,........ ....,....
.6 " "-:"'" "' "" -""
• 20
m
10 ....
-90 -§0 -30 0 30 60 90
Latitude
Figure 4: Latitude-Altitude distribution of percent change in
ozone due to NOx injection, Model G.
368
4O
3O
20
lO
o
-9o
m
-60 -30 0 30 60 90
Latitude
Figure 5: Same as figure 4, for Model H.
Aircraft Gas Phase Gas Phase +
Type Chemistry Het. Chemistry
Mach 2.4 -1.28 -0.06
(16.8-19.8 km)
Mach 3.2 -4.5 -2.2
(21.3-24.4 km)
Table I: Calculated percent change in global ozone.
tions are considered (model G), ozone lossesoccur in the
region above 10 km where the NOx catalyticcycleisdom-
inant. There is some increase in the tropospheric ozone
which is partly due to increased production from smog
reactions. For the model with heterogeneous reactions,
ozone reductions are confined to the region between 22
and 35 kin. Below thisregion ozone increasesby about i
to 3%
The main reason for this change in the ozone response
to NOx injection is the modification of the photochem-
istry by the heterogeneous reactions, especially reaction
(1). By converting reactive NO_ into HNO3, this reac-
tion effectively alters the relative importance of various
catalytic cycles in destroying odd oxygen. The ratio of
the odd oxygen loss rate due to NOx cycle as a percent
of the total odd oxygen loss rate is shown in Figure 6 for
July. The solid lines represent results from model H, and
the dashed lines represent model G. The contribution of
NOx catalytic cycle is clearly reduced to about 10% in the
lower stratosphere because of the heterogeneous reactions.
Correspondingly, there are increases in the odd oxygen loss
3O
25
,_ 20
15
-90 -60 -30 0
Latitude
30 60 90
Figure 6: Ratio, in percent, of odd oxygen loss rate due to
NOx catalytic cycle to the total odd oxygen loss rate. Solid
fines denote model with heterogeneous chemistry; dashed lines
represent model with gas phase chemistry only.
369
due to Clx catalytic cycle. With the reduced significance
of the NOx cycle, the atmosphere with heterogeneous re-
action becomes less sensitive to NOx perturbations from
stratospheric aircraft. Ozone increases, in the lower alti-
tudes nearly balance the ozone reductions in the upper re-
gions, with the result that there is very little change in the
total ozone in model H for the Mach 2.4 case. If the cruise
altitude is higher, as in the case of Mach 3.2 aircraft, there
will be larger ozone reductions in the mid stratosphere,
and some reduction in the total ozone also. But even in
this case, total ozone reduction is less for an atmosphere
with heterogeneous reactions. The results from our model
study are summarized in Table I.
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Callis, L. B., R. E. Boughner, M. Natarajan, J. D. Lam-
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Impact of stratospheric aircraft emissions on ozone: A two dimensional model study

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