Geoscience Reference
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The reaction between NO and HO
2
in all the cases considered, favors a decrease
of HO
2
concentration. In some cases the calculated values of OH concentration
doubled, but at a maximum level of NO
x
concentration the loss of hydroxyl due to
the reaction OH + NO
2
compensates the formation of hydroxyl due to reactions
NO
2
+ NO. An additional increase of OH by 30
60 % can, however, result from
-
convective transfer of CH
3
COOH.
To form an estimate of the contribution of lightning and anthropogenic sources
to the formation of NO
x
concentration on global scales, Kurz and Grewe (2002)
undertook a numerical modeling of the frequency and global distribution of
lightning strikes and the resulting formation of NO
x
using the complex model of
climate and chemical processes taking place in the atmosphere ECHAM4.L39
(DRL)/CHEM(E39/C), whose important feature is a realistic simulation of pro-
cesses responsible for the formation of penetrating convection.
Calculated estimates of the height of convective clouds, on the whole, agree well
with those observed. But in mid-latitudes of Western Europe the calculated values
were underestimated. The calculated spatial distribution of lightning strikes agrees
well with the observed distribution, though the calculated ratio of the density of
strikes over land and over the oceans turned out to be underestimated. In the mid-
latitudes of Western Europe the density of strikes is underestimated compared to
that observed, which can be explained by inadequate scheme of convection
parameterization.
According to numerical modeling results, the NO
x
formation is most intensive in
the tropics and in mid-latitudes, and is clearly separated (in space) from NO
x
emissions due to aviation. The lightning-induced maximum level of NO
x
emissions
is located at altitudes approximately 5 km below the level of the tropopause, with
the level of emissions exceeding 3 times the respective anthropogenic level. Besides
this, it is important that maximum aircraft emissions of NO
x
tend to be at much
higher altitudes and farther north (being concentrated mainly within the North-
Atlantic corridor 30
N at a level of about 200 h Pa, that is, 12 km) compared to
NO
x
formed due to lightning strikes.
Zhang et al. (2003a, b) analyzed the possibilities of numerical modeling of
nitrogen oxides formed due to lightning strikes using the 2D version of the model
that simulates an electrization of the storm. It is supposed that the formation of NO
is determined by dissipation of energy, whose value is calculated from the value of
the electric
60
°
-
field before and after a lightning strike. The rate of formation of energy
responsible for NO formation is 9.2
10
16
molecules J
−
1
. Considering a limited set
of chemical reactions in which NO, NO
2
, and O
3
participate, a numerical modeling
has been carried out of processes taking place in a small storm with 10 intra-cloud
strikes during 2 min. The level of dissipation of energy varied between 0.024 and
0.28 GJ. After cessation of lightning strikes the integration continued during 18 min
more. Analysis of the modeling results has shown that the mixing ratio of NO
formed within a cloud (by order of magnitude) is 10 ppb after most powerful strikes
and 1
×
2 ppb on the windward side of the thundercloud anvil at the end of the
integration interval. These estimates agree with the data of observations. A com-
parison with results of the earlier numerical modeling with the use of different 2D
-
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