As a consequence of the non-linear behavior of the chemistry of the atmosphere and because of the short lifetime of nitrogen oxides (NO(x)), two-dimensional models do not give an adequate description of the production and destruction rates of NO(x) and their effects on the distributions of the concentration of ozone and hydroxyl radical. In this study, we use a three-dimensional model to evaluate the contribution of increasing NO(x) emissions from industrial activity and biomass burning to changes in the chemical composition of the troposphere. By comparing results obtained from longitudinally-uniform and longitudinally-varying emissions of NO(x), we demonstrate that the geographical representation of the NO(x) emissions is crucial in simulating tropospheric chemistry

Crutzen, Paul J.

Kanakidou, Maria

Zimmermann, Peter H.

English

NASA Technical Reports Server

N95- 10605
3o" /73
ESTIMATES OF THE CHANGES IN TROPOSPHERIC CHEMISTRY WHICH RESULT FROM
HUMAN ACTIVITY AND THEIR DEPENDANCE ON NO X EMISSIONS AND MODEL
RESOLUTION
Maria K anakido u
Centre des Faibles Radioactivitts, Laboratoire mixte CNRS/CEA, Domaine du CNRS, F-91198 Gif-sur-Yvette
Cedex, France.
Paul J. Crutzen and Peter H. Zimmernm_
Max Planck Institute for Chemistry, Atmospheric Chemistry Division, P.O.Box 3060, D-6500 Mainz, Germany.
ABSTRACT
As a consequence of the non-linear behavior of the
chemistry of the atmosphere and because of the short lifetime
of nitrogen oxides (NOx), two-dimensional models do not
give an adequate description of the production and destruction
rates of NO x and their effects on the distributions of the
concentration of ozone and hydroxyl radical.
In this study, we use a three-dimensional model to
evaluate the contribution of increasing NO x emissions from
industrial activity and biomass burning to changes in the
chemical composition of the troposphere. By comparing
results obtained from longitudinally-uniform and
longitudinally-varying emissions of NO x, we demonstrate that
the geographical representation of the NO x emissions is crucial
in simulating tropospheric chemistry.
1. INTRODUCTION
The impact of anthropogenic trace gas emissions on
ozone (0 3) and hydroxyl radical (OH) concentrations and
generally on the oxidizing efficiency of the troposphere is a
matter of great concern. There have been many modeling
efforts devoted to simulating tropospheric chemistry and
examining trends in the atmospheric concentrations of
important trace gases (e.g. Isaksen and Hov, 1987; Crutzen
and Zimmermann, 1991). However, the ability of models to
adequately account for non-linear chemical interactions
affecting the distributions of nitrogen oxides (NOx), 0 3 and
OH needs to be examined carefully.
In this study, we use a three-dimensional model to
evaluate the contribution of increasing NO x emissions from
industrial activity and biomass burning to changes in the
chemical composition of the troposphere. By comparing
results obtained from longitudinally-uniform and
longitudinally-varying emissions of NO x, we demonstrate that
the geographical representation of the NO x emissions is crucial
in simulating tropospheric chemistry.
2. MODEL DESCRIPTION
The model used is a climatological three-dimensional
global model of the troposphere with a 10 ° latitude x 10 °
longitude spatial resolution. It contains 10 vertical layers from
the surface to 100 hPa. The model design is described in detail
by Zimmermann et al. [1989] and Crutzen and Zimmermann
[1991]. The parametrization of deep cumulus convection,
which is of particular importance for _,hort-lived tracers, is
decribed by Feichter and Crutzen [1990]. In its current form,
the model is coupled with a chemical scheme containing about
100 photochemical reactions describing the 0 3 - OH - NO x -
CO - CH 4 - C2H 6 - C3H 8 chemistry. The transport of 20
species in the troposphere is considered, whereas transport
processes are neglected for another 31 species which are
assumed to be in photochemical steady-state [Kanakidou et al.,
1991]. A time step of 2 hours is used.
In the present study downward fluxes of 0 3 at 100 hPa
that vary monthly and latitudinally are adopted totalling
approximately 300 Tg-O3/Yr. Global NO x emissions amount
to 34 Tg-N/yr. Their adopted distribution is discussed later. We
also adopted CO surface emissions that vary monthly
(including indirect CO emissions by oxidation of the NMHC
other than C2H 6 and C3H 8) totalling about 1700 Tg CO/yr.
C2H 6 and C3H 8 emissions amount to 15 Tg-C2H6/Yr and 17
Tg-C3H8/Yr, respectively, and vary by longitude, latitude, and
month. CH 4 volume mixing ratios at the lower boundary are
assigned, according to observations (Steele et al., 1987). Other
66
https://ntrs.nasa.gov/search.jsp?R=19950004193 2020-06-16T11:46:58+00:00Z
featuresofupperandlowerboundary conditions used in the
model are described in Crutzen and Zimmermann [1991] and
Kanakidou et al. [1992].
Case Studies.
We will concentrate on the impact of NO x emissions
from industry and biomass burning on the oxidizing efficiency
of the atmosphere. We will then evaluate uncertainties in the
computed concentrations of OH radicals and in the net
chemical production of 0 3 related to the distribution of NO x
emissions.
For this purpose, 5 different scenarios of longitudinally
and latitudinally varying NO x emissions have been considered:
In the base case, NO x industrial emissions of 20 Tg N/yr are
distributed proportional to the industrial CO 2 emissions
[Marland and Rotty, 1984] and when possible readjusted to fit
the NO x emission data published by World Resources Institute
[1990]. Tropical NO x emissions of 6 Tg N/yr from biomass
burning are spatially distributed according to the analysis of
Hao et al. [1990]. These emissions occur mainly during the
dry season in the tropics and subtropics. NO x emissions from
lightning totalling 5 Tg N/yr were varied spatially and
temporally and are based on flash frequency observations
[Turman and Edgar, 1982]. Another 4 Tg N/yr released by
soils are distributed as a function of soil productivity [Crutzen
and Zimmermann, 1991]. In the other 4 cases, we adopted the
emissions of NO x from industry and biomass burning shown
in Table I. The NO x emissions by lightning and by soils are
the same as in the base case.
3. RESULTS AND DISCUSSION
Changes in the chemical composition of the atmosphere due to
increasing NOx emissions from industry and biomass burning.
The chemical production and destruction of 0 3 in the
troposphere and the global tropospheric annual mean diurnal-
average OH concentration computed for each of the 5 case
studies are presented in Table 1.
Focusing on the chemical production and destruction of
03 in the troposphere computed when NO x emissions by
industry are neglected and those computed for the present day,
we can derive that 26% of the present day net chemical
production of 0 3 (664 Tg-O3/Yr ) in the troposphere could be
due to NO x emissions by industrial activity. This is the net
result of increasing both chemical production (+17%) and
chemical destruction ofO 3 (+14%) when NO x emissions are
increasing (from 0 to 20 Tg-N/yr).
Table i. Adopted global NO x emissions by industry (E l) and
biomass burning (E B) (in Tg N/yr). Chemical production
(PO3), chemical destruction (DO 3) and net chemical
production (PO 3 - DO3) of 0 3 in the troposphere (in Tg
O3/Yr ) and global tropospheric annual mean diurnal average
OH concentration (in 106 cm-3).
EI EB PO 3 I)O 3 PO 3 - DO 3 OH
20 6 3013 2349 664 0.83
0 6 2511 2020 491 0.72
20 0 2837 2222 615 0.76
40 6 3275 2518 757 0.89
20 12 3113 2405 708 0.85
The difference in the net chemical production of O 3
calculated without consideration of NO x emissions by biomass
burning (615 Tg-O3/Yr) from that calculated for the base case
(644 Tg-O3/Yr) shows that only about 5% could be due to
emissions by biomass burning. Similarly, NO x industrial
emissions may explain up to 13% of the changes in the global
tropospheric mean OH concentration whereas the impact of
biomass burning NO x emissions on this OH concentration
reaches 8%. Note however that in this study we do not take
into account changes in the emissions of NMHC and CO or the
concentrations of CH 4.
Doubled industrial emissions of NO x will perturb the
OH global mean value by only 7% (0.89 10 6 cm -3 instead of
0.83 106 cm -3 in the base case) and the 0 3 net chemical
production by about 14% (757 Tg-O3/Yr compared to 664 Tg-
O3/Yr ). This percent change is about half the present day effect
of NO x emissions by industry on the net chemical production
of 0 3 , which as above mentioned, is 26%. This clearly
demonstrates that the effect of NO x emissions on tropospheric
chemistry is not directly proportional to the amount of NO x
emitted into the atmosphere.
Doubled NO x emissions from industry or biomass
burning do not imply a double impact of NO x on tropospheric
chemistry. These calculations suggest that the changes in the
chemical composition of the atmosphere are not linearly related
to the changes in NO x emissions.
Differences between results ol)t_lin¢_J with longitudinally-
oniform and v_a'ying emissions of NOx.
67
Kanakidou and Crutzen [1992] demonstrated by
running a three-dimensional model both with longitudinally-
uniform (2-D) and varying (3-D) NO x and NMHC input rates
that the use of varying input rates leads to significantly lower
03 and OH concentrations.
Here we examine the differences between results
computed with "2-D" distribution of NO x emissions and those
computed with "3-D" distribution of NO x emissions and in
addition to the earlier study we discuss the dependence of these
differences on the amount of NO x emitted by industry and by
biomass burning. We produced a second series of 5
simulations using a longitudinally-uniform distribution of NO x
emissions summing up at each latitude to those used in the
previous cases, respectively. This second series of simulations
should reproduce the main features of the results which are
obtained with two-dimensional models. A direct comparison
between two-dimensional and three-dimensional models is not
strictly possible because of non-equivalent transport
formulation.
We compare the results obtained with longitudinally-
uniform NO x emissions to those obtained with longitudinally-
varying NO x emissions. In Table 2 we report the percent
differences for the 5 studied scenarios of NO x emissions from
industry and biomass burning.
Table 2. Differences (in percent) between values computed
with longitudinally-uniform (2-D) and those computed with
longitudinally-varying (3-D) NO x emissions ( [2-D - 3-D] / 3-
D xl00) for the 5 senarios of NO x emissions by industry (El)
and by biomass burning (EB)'
El E B % in the 0 3 % in the OH
net chem. production global annual mean
a. Industrial emission scenarios *
0 6 16 16
20 6 16 14
40 6 16 14
b. Biomass burning emission scenarios **
20 0 13 12
20 6 16 14
20 12 18 17
* in increasing order of industlial emissions of NO x.
* * in increasing order of biomass burning emissions of NO_.
The results of this comparison agree well with the earlier
study by Kanakidou and Crutzen, [1992] and the reader is
referred to this paper for further information regarding the
spatial and temporal variation of the computed differences in
03, NO x and OH concentrations.
We focus here on the dependence of the degree of non-
linearity (i.e. of the computed differences between "2-D" and
"3-D" global tropospheric amounts) on the amount of NO x
emitted in the atmosphere. As shown in Table 2, increasing
emissions of NO x by biomass burning lead to an increase in
the differences between the computed "2-D" and "3-D" 03 net
chemical production and OH global tropospheric mean
concentration. This is not the case for increasing NO x
emissions from industry mainly in the northern hemisphere
where zonal mixing by the winds is more effective than at the
equator. The strong dependence of the computed results on the
strength of the NO x source in the tropics is probably due to the
relatively small zonal mixing by the winds, implying that the
assumption of longitudinally-uniform emissions of NO x leads
to large inaccuracies in the computed 0 3 and OH
concentrations in this region.
Furthermore, the difference between the results
computed with longitudinally uniform and those computed
with longitudinally varying emissions depend also on the
adopted CO levels. For instance, a preliminary test of
sensitivity of these differences to CO emissions shows that a
reduction on the surface CO emissions by a factor of 3 (to
about 500 Tg/yr instead of about 1700 Tg/yr adopted in this
study) leads to a higher degree of non-linear dependence of the
net chemical production of 0 3 on NO x emissions (up to 23%
compared to 18%) but simultaneously to smaller differences
between the 2-D and 3-D computed OH concentrations (9% to
12%).
4. CONCLUDING REMARKS
These results clearly show that 0 3 and OH
concentrations computed with longitudinally-uniform
emissions of NO x are higher than those computed with
logitudinally-varying emissions. However, the relationship
between the overestimation of the computed 0 3 and OH
concentrations and the adopted distribution and strength of the
NO x atmospheric sources is not straightforward. Thus, the
accuracy in NO x emissions data is crucial to simulating
changes in tropospheric chemistry resulting from human
,activity.
68
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Estimates of the changes in tropospheric chemistry which result from human activity and their dependence on NO(x) emissions and model resolution

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