|
Items in cart [1] |
Questions? Call 888-624-8373 |
| Copyright © 2009. National Academy of Sciences. All rights reserved. Terms of Use and Privacy Statement |
Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 70
6
INTRODUCTION
The Role of Lightning in the Chemistry
of the Atmosphere
WILLIAM L. CHAMEIDES
Georgia Institute of Technology
ABSTRACT
The high temperatures in and around the discharge tube of a lightning stroke cause the dissocia-
tion of the major atmospheric constituents N2, 02, C02, and H2 and the formation of trace
species such as NO, CO, N2, OH, N. O. and H. As this cylinder of hot air cools, the levels of these
trace species drop. However, if the cooling is sufficiently rapid the concentrations of these trace
species can be "frozen-in" at levels significantly above their ambient, thermochemical equilib-
rium abundances, thereby leading to a net source of these gases to the background atmosphere. It
is estimated that about 3 tg of N yr- ~ as NO are produced in the present-day atmosphere by
lightning through this process. Other gases produced by lightning are CO and N2O in the Earth's
atmosphere; HCN in the Earth's prebiological atmosphere; CO, NO, and O2 in the cvtherian
atmosphere; and CO, N2, and a variety of hydrocarbons in the Jovian atmosphere. The major
uncertainty in quantifying the role of lightning in the chemistry of the terrestrial atmosphere, as
well as that of other planetary atmospheres, arises from the lack of accurate statistics on the
energy and frequency of lightning. The role of coronal discharges in the chemistry of clouds also
needs to be investigated.
In addition to the spectacular visual and aural effects
that accompany a lightning flash, intense chemical re-
actions occur, which, on a relatively short time scale,
can radically alter the chemical composition of the air in
and around the discharge tube and, on longer time
scales, can ultimately affect the composition of the at-
mosphere as a whole. The short-term chemical changes
associated with lightning have been well documented
by spectroscopic studies of lightning strokes (cf., Sa-
lanave, 1961; Uman, 1969~. For instance, the strong
70
emissions from neutral atomic nitrogen (N If, singly io-
nized atomic nitrogen (N all, neutral atomic oxygen
(O If, and singly ionized atomic oxygen (O ~) typically
observed from the hot core of discharges, are indicative
of the widespread dissociation of atmospheric N2 and O2
and the subsequent ionization of their atomic daugh-
ters. Other prominent spectroscopic features are the
emission lines from CN and H. species arising from the
dissociation of CO2 and H2O.
For the most part the large changes in the chemical
composition of the air in and around the discharge tube
can be related to the rapid variations in temperature in
OCR for page 71
THE ROLE OF LIGHTNING IN THE CHEMISTRY OF THE ATMOSPHERE
this region. The lightning bolt and associated shock
wave produce a cylinder of very hot air within which
chemical reactions between the atmospheric gases pro-
ceed rapidly to bring the mixture into thermochemical
equilibrium. Immediately after the energy deposition,
the temperature in the discharge tube approaches
30,000 K and the gas is a completely ionized plasma. As
the gas cools by hydrodynamic expansion and turbulent
mixing, the equilibrium composition of the gas changes
from a plasma to a mixture of neutral atoms such as N
and O and then to a mixture of molecular species and
ultimately as the temperatures return to ambient to a
mixture of N2, 02, H2O, and CO2 much like the back-
ground composition of the atmosphere. This variation
in the equilibrium composition of air as a function of
temperature is illustrated in Figure 6.1; note that as the
temperatures fall below 5000 K the equilibrium shifts
from N. O. H. and CO to NO, OH, and CO and then to
N2, 02, H2O, and CO2.
If the gas around the lightning discharge was always
to remain in thermochemical equilibrium, the net effect
of lightning on the atmospheric composition would be
negligible; once the temperature of the gas returned to
its ambient level, its composition would be essentially
the same as that of the background atmosphere's, and
thus there would be no net production or destruction of
atmospheric chemical species by lightning discharges.
On the other hand, it is well known that laboratory
sparks can have significant effects on the composition of
air; most notable is the fixation of atmospheric nitrogen
(N2) by sparks to produce nitric oxide (NO). Given the
basic equivalence between laboratory sparks and light-
ning discharges it would seem reasonable to expect that
lightning also affects the composition of air. In fact, the
knowledge that NO is produced by laboratory sparks led
von Liebig to propose in 1827 that the NO 3 typically
observed in rainwater arises from the fixation of atmo-
spheric N2 by lightning discharges. This nineteenth cen-
tury hypothesis of von Liebig's has only recently been
qualitatively confirmed by direct observations of en-
hanced levels of NO and NO2 in and around active thun-
derclouds (Noxon, 1976, 1978; Davis and Chameides,
1984) and in the vicinity of a cloud-to-ground lightning
flash (Drapcho et al., 1983~.
The identification of the mechanisms responsible for
the net production of trace species such as NO by light-
ning and the quantification of their source rates on a
global scale define the current frontier in the field of the
chemistry of atmospheric lightning and will, therefore,
be the major subject of this review. The discussion be-
gins by focusing on the production by lightning of atmo-
spheric NO, a species of special interest because of its
central role in the photochemistry of the atmosphere
10 '
10-2
rat
in.
O_
10-3
=-4
10-5
71
_ I'::
1000 2000 3000 4000 5000
T [°K]
FIGURE 6.1 Equilibrium volume mixing ratios of selected atmo-
spheric species as a function of temperatures in heated tropospheric
air.
(cf., Crutzen, 1983~. Following the discussion of NO
production by lightning, a more general presentation
will be given of the production of other trace species in
both the present and the prebiological, terrestrial atmo-
sphere, as well as in other planetary atmospheres. A
brief discussion is then presented on the possible effect of
electrical discharges on the chemistry of cloudwater and
the generation of acids in precipitation. Finally, a brief
outline of the needs for future work in this area is pre-
sented.
OCR for page 72
72
NO PRODUCTION BY LIGHTNING
Similar to the Z'elovich mechanism for the fixation of
nitrogen in explosions (Z'elovich and Raizer, 1966), the
production of NO in lightning discharges is believed to
be driven by high-temperature chemical reactions
within a rapidly cooling parcel of air; the rapid cooling
causes NO levels above its thermochemical abundance
to be "frozen" into the gas. A simple physical analogy to
this chemical production mechanism is that of dropping
a bead through a column of rapidly cooling water in a
gravitational field. Because the bead wants to minimize
its potential energy with respect to the gravitational
field, the bead will tend to fall to the bottom of the wa-
ter column. If, however, the water were to cool so rap-
idly that it froze before the bead reached the bottom of
the column, the head would be frozen in the column at a
position of higher potential energy and would be pre-
vented from reaching its energetically preferred posi-
tion at the bottom of the column.
In the case of NO production in lightning, the high
temperatures in and surrounding the discharge channel
result in a series of chemical reactions that both produce
and destroy NO. NO production is initiated by the ther-
mal dissociation of O2.
O2 ~ ~ O + O (Reaction6.1)
followed by the production of NO via the reaction chain
O + N2 - NO + N (Reaction6.2)
and
N + O2 - NO + O. (Reaction6.3)
In competition with these NO-producing reactions are
NO + N ~ N2 + O (Reaction6.4)
and
NO + O ~ N + 02, (Reaction6.5)
which convert NO back to N2 and O2 as well as
NO ~ - N + O. (Reaction6.6)
the thermal dissociation of NO itself, and
NO + NO - N2O + O. (Reaction6.7)
the formation of N2O from NO.
The equilibrium NO concentration, /°O, is the NO
level at which NO-producing and NO-destroying reac-
tions are in balance. As illustrated in Figure 6. 2, f° O is a
strong function of temperature. As the temperature rises
above 1000 K the dissociation of N2 and O2 causes an
increase in the NO equilibrium level. At about 4000 K,
WILLIAM L. CHAMEIDES
f ) O peaks at a value approaching 10 percent. For higher
temperature, N and O atoms become increasingly more
stable relative to NO (See Figure 6.2) and; ~ O decreases.
Thus if NO were always to maintain thermochemical
equilibrium, its concentration would reach a maximum
when the temperature in and around the discharge tube
was ~ 4000 K and would then decrease to a negligibly
small value as the heated air cooled to ambient tem-
peratures. However, similar to the equilibrium NO
concentration, the time, TNo, required to establish ther-
mochemical equilibrium for NO also varies with tem-
perature. As illustrated in Figure 6. 2, this time becomes
increasingly longer as temperature decreases because
the reactions acting to establish equilibrium become
slower. (In this figure, TNo was calculated by summing
the loss frequencies for NO due to Reactions 6.4-6.7.)
Whereas only a few microseconds are required for NO
to equilibrate at 4000 K, equilibrium requires millisec-
onds at 2500 K, a second at 2000 K, and approximately
103 years at 1000 K. Hence, as the air cools, a tempera-
ture is eventually reached at which the rates of reaction
10-' ~ ~, ~ lOt
1 /\
1/ \
aeo-2 ~\
/ ~X'os
0-3~ 1 1l \\
0-4 1 ~\ ~ 1o~2
0-5 ~10-3
. .i . 1 ~ 10-4
0oo 2000 3000 4000 sooo 6000
10-6
TEMPERATURE, °K
10°
FIGURE 6.2 The NO equilibrium volume mixing ratio f`', repre-
sented by the solid curve, and the NO chemical lifetime TNo, repre-
sented by the dashed curve, as a function of temperatures in heated
tropospheric air. (After Borucki and Chameides, 1984.)
OCR for page 73
THE ROLE OF LIGHTNING IN THE CHEMISTRY OF THE ATMOSPHERE
become too slow to keep NO in equilibrium. Instead of
falling to the thermochemical equilibrium concentra-
tion of the ambient temperature, a higher NO level be-
comes frozen into the gas. This higher concentration,
which corresponds to the NO equilibrium level at the
temperature at which the NO concentration departs
from equilibrium, is called the "freeze-out" tempera-
ture.
The freeze-out temperature of NO, TF, is approxi-
mately determined by the relationship
TT; TF\) = TNO ~ TF),
(6.1)
where TT iS the characteristic cooling time of the heated
air. When T > TF, then TNO < TT and the chemical reac-
tions are sufficiently rapid to keep NO in the thermo-
chemical equilibrium. However, for T IT
and chemical reactions are too slow to adjust to the rap-
idly decreasing T;NO, therefore, freezes out with a mix-
ing ratiof° o(TF). Although a lower abundance of NOis
favored thermodynamically at low T. the kinetics are
too slow for readjustment. P. the net yield of NO pro-
duced by this process, is then approximated by
P(NO) =f°o(TF)M(TF)Eo imoleculesl~i, (6.2)
where M is the number of molecules per meter heated
to, or above, TF in the region where NOis being pro-
duced for a discharge energy of En (in units of l/m). Thus
it is necessary to determine values for TF and M that,
when combined with the results of Figure 6.2, will al-
low an estimate of P(NO) from Eq. (6.2~.
Once P(NO)is obtained, the global rate of NO pro-
duction by lightning, ¢(NO), can be estimated from
¢(NO)=P(NO). R
(14g/mole) (10-~2tg/g) (3.16 x 107 sec/yr) `6 3'
(6.02 x 1023 molecules/mole)
in units of teragrams (tg) (i.e.,10 ~ 12 gor 106 metric tons)
of N per year, where R is the number of joules dissipated
globally by lightning per second. Because of the current
interest in developing global budgets for the flow of
fixed nitrogen and nitrogen oxides through the atmo-
sphere, reasonably accurate estimates for ¢(NO) are de-
sirable. A brief discussion of how the parameters needed
to solve ¢(NO) are calculated is presented below.
Estimate of P(NO)
Following the approach of Borucki and Chameides
(1984), we infer values for TF and M that are needed to
73
calculate P(NO) in Eq. (6.2) from the laboratory study
of linear discharge channels by Picone et al. (1981~. This
study indicated that lightning-like discharge channels
cooled with a TT of about 2.5 x 10-3 sec. For this choice
°f TT, TF andf° o(Tf) can be estimated from Figure 6.2 to
be about 2660 K and 0.029, respectively. Furthermore,
using the result of Picone et al. (1981) that in spark dis-
charges 1 ~ of energy is required to heat each 1 cm3 of air
to a temperature of 3000 K and assuming that the gas
cools from 3000 K to the freeze-out temperature of 2660
K by mixing with the ambient atmosphere, it can be
inferred that
M(2660K)IEo = 3.2 x 10~9molecules/~. (6.4)
Substituting the above values for/° o(TF) and M(TF)/EO
into Eq. (6.2),
P(NO) = (0.29) (3.2 x 10~)
= 9.2 x 10~6molecules/~. (6.5)
A comparison of the above-estimated NO yield with
those of previous investigators is presented in Table 6.1
and indicates a rather good agreement with a wide vari-
ety of theoretical calculations, laboratory spark experi-
ments, and atmospheric measurements. The largest dis-
crepancy appears to be with the NO yield attributed to
Drapcho et al. (1983~. The yield of Drapcho et al. was
based on their observation of a sudden increase in NO
and NO2 levels in the vicinity of a cloud-to-ground dis-
charge; given the many assumptions necessary to infer a
yield from this observation the disparity between the
yield of Drapcho et al. and the others in Table 6.1 is not
· ~
very surprlslng.
The Global Dissipation Rate, R
The rate at which energy is dissipated by lightning
globally can be expressed as a function of two other pa-
rameters, i.e.,
R = EF F.
(6.6)
where EF is the average number of joules dissipated per
lightning flash and F is the number of lightning flashes
occurring globally per second. Borucki and Chameides
(1984) recently examined the existing data base on light-
ning flashes to estimate these parameters. Combining
optical and electrical measurements of the energy of a
single stroke, observations of the number of strokes per
flash, as well as measurements of the distribution of en-
ergy among the first and subsequent strokes, EF was esti-
mated to be about 4 x 108 ]/flash with a factor of 2.5
uncertainty. From satelliteborne optical detection sys
, . ..
. ~.
OCR for page 74
74
TABLE 6.1 Estimates of NO Yield from Lightning Discharge
P(NO) (molecules/J)
(9 + 2) x 1016
WILLIAM L. CHAMEIDES
Investigator
Based on the calculations of
A. This work
Borucki and Chameides (1984)
B. Theoreticalcalculation 3 x 1Oi6a Tuck(1976)
(3-7.5) x 10~6 Chameides et al. (1977)
(4-6) x 10'6a Griffing(1977)
80 X 10~6 b Hill et al. (1980)
16 x 10~6 Hill et al., as corrected by
Borucki and Chameides (1984)
(8-17) x 10~6 Chameides (1979)
C. Laboratory spark (6 + 1) 10~6 Chameideset al. (1977)
experiment (5 + 2) x 10~6 Levine et al. (1981)
(2 + 0.5) x 10~6 Peyrous and Lapeyre (1982)
D. Atmospheric measurement (20-30) x 10~6a Noxon(1976)
(25 2500) X 1016 a Drapcho et al. (1983)
aThe NO yields obtained by these investigators were expressed as molecules/flash. These yields were converted to units of molecules/Joule by
assuming EF = 4 X 108 J/flash.
bDerived from Hill et al. (1980) by dividing their NO yield (6 x 1025 molecules/flash) by their energy per flash [(1.5 x 104 Jim) (5 x 103 m/flash)~.
tems, a value of 100 flashes/sec was assigned to F by
Borucki and Chameides (1984) with an uncertainty fac-
tor of 25 percent. Substituting these parameters into Eq.
(6.6), R was thus estimated to be about 4 x 10~° W with
a possible range of (1.3 to 12) x 10~° W.
The Global NO Production Rate, ¢(NO)
The above estimates for R and P(NO) can be com-
bined in Eq. (6.3) to yield a global NO production rate
of ~ 2.5 tg of N/yr. However, it should be noted that this
number is highly uncertain; Borucki and Chameides
(1984) in a similar analysis arrived at a possible range in
¢(NO) from 0.8 to 8 tg of N/yr. By far the largest source
of uncertainty arises from the uncertainty in EF, the en-
ergy dissipated by a lightning flash. A comparison be-
tween the estimate for the global fixation rate calculated
here and those of previous investigators is presented in
Table 6.2. For the most part our result is consistent
with, although somewhat smaller than, the other esti-
mates.
Biological processes fix atmospheric N2 at a rate of
about 200 tg of N/yr and anthropogenic fixation (pri-
marily due to the synthesis of fertilizers) occurs at a rate
of about 60 tg of N/yr (Burns and Hardy, 1975~. Thus it
would appear that, at present, lightning is responsible
for at most a few percent of the Earth's total nitrogen
fixation. On the other hand, lightning appears to repre-
sent one of, if not the, major natural source of NOX to the
atmosphere. The other natural sources of atmospheric
NOr include stratospheric oxidation of N2O at a rate of
0.6 tg of N/yr (Levy et al., 1980~; oxidation of NH3,
which is not well known but could be important (Mc
TABLE 6.2 Estimates of the Amount of Nitrogen Fixed by
Lightning
Investigator
Tuck (1976)
Chameideset al. (1977)
Chameides (1979)
Dawson (1980)
Hill et al. (1980)
Levine et al. (1981)
Kowalczyck and Bauer (1982)
Ehhalt and Drummond (1982)
Peyrous and Lapeyre (1982)
Logan (1983)
Drapchoet al. (1983j
Present result [based on
calculations of
Borucki and Chameides (1984)]
al tg = 1012 g = 106 metric tons.
Nitrogen Fixed
per Year (tg)a
4.2
30to40
35 to 90
3
4.4
1.8
5.7
30
Best Estimate: 2.6
Range: 0.8 to 8
Connell, 1973~; and NO emissions from soils as a result
of microbial activity at a rate of (1 to 10) tg of N/yr
(Galbally and Roy, 1978; Lipschultz et al., 1981~. As
noted earlier, qualitative confirmation of the impor-
tance of lightning as a natural source of atmospheric
NOX has been obtained from a variety of NO and NO2
measurements (Noxon, 1976, 1978; Drapcho et al.,
1983; Davis and Chameides, 1984), which reveal anom-
alously high concentrations of NO and NO2 in air within
and above clouds in remote regions of the globe. In re-
gions strongly affected by anthropogenic activities,
however, this natural NO source is swamped by NO
production from the burning of fossil fuel and biomass
OCR for page 75
THE ROLE OF LIGHTNING IN THE CHEMISTRY OF THE ATMOSPHERE
at a combiner] rate of about 30 tg of N/yr (Crutzen,
1983~. It is for this reason that NOX levels in urban areas
are some 104 to 105 times higher than in remote regions
of the marine atmosphere (McFarland et a]., 1979) and
in conjunction with the anthropogenic release of non-
methane hydrocarbons is the cause of photochemical
smog and related air pollution problems. Nevertheless,
it is interesting to note that even the extremely low levels
of NOX that are characteristic of the remote troposphere
are believed to have a significant effect on the chemistry
of the atmosphere, catalyzing the photochemical pro-
duction of tropospheric O3 and enhancing OH levels
(Logan et at., 1981; Davis and Chameides, 1984~. To
the extent that lightning is responsible for the NOX levels
in the remote troposphere, it would appear that light-
ning plays an important role in the photochemistry of
the atmosphere.
~1~ ~ 1~ T TO L! ~ _ 1 _ 1 ~_ 1 1 ~. 1 1 ~r _ ~
75
OTHER TRACE GASES PRODUCED BY
LIGHTNING
While NO has received the bulk of the attention with
regard to production by lightning because of its impor-
tance in the photochemistry of the atmosphere, research
has revealed that a myriad of other trace gases in addi-
tion to NO can be generated by lightning in a variety of
interesting environments. These gases and their yields in
electrical discharges as determined by both theoretical
calculations ant! laboratory experiments are listed in
Table 6.3. The comparison between experimentally and
theoretically derived yields is quite good over a wide
range of gases and atmospheric compositions.
The production of HCN in a reducing, prebiological
terrestrial atmosphere is of particular interest because it
has been proposed that lightning-produced HCN was an
1 EDEN O.O ~alcularea ana ~xperlmentally L'erlvecl Y 1elds of 1 race Gases in Various Atmospheresa
S.
pecles
Calculated Yield
(molecules/J)
A. Present-Day Terrestrial Atmosphere
NO 9 x 1016
CO (0.1-5) x 1014
N2O (3-13) x 1012
B. Reducing Prebiological Terrestrial Atmosphere (95 % N2, 5 % CH4)
HCN (6-17) x 1016
C. Cytherian Atmosphere (95 % CO2, 5 To N2)
CO (1-1.4) x 1017
NO (5-6) x 1015
(O~ + O) (6-9) x 1016
D. Jovian Atmosphere (99.95 % H2, 0.05 % CH4)
CO5 x 1015
5 x 1014
x loll
x loll
X 1012
X 1011
X 1011
1011
N2
HCN 9 x 1013
C2H2 3 x 1013
C2H ~2 x 1012
HCHO 8 x 10
COG 3 x 10
C2H6 4 x 1011
E. Titan Atmosphere (97 % N2, 3 % CH4,
HCN 1.2 x 101'
C~N2 2.5 x 1014
C2H2 7.5 x 1015
C2Hi SX1
aReferences:
1. Borucki and Chameides (1984)
2. Chameides et al. (1977)
3. Levine et al. (1981)
4. Peyrous and Lapeyre (1982)
5. Chameides (1979)
6. Levine et al. (1979)
7. Chameides and Walker (1981)
8. Sanchez et al. (1967)
Experimental Yield
J~L=W
(2-6) x 1016
1 x 1014
4 x Boll
~ loll
3 x 1016
4 x 1015
9. Bar Nun and Shaviv (1975)
10. Bar Nun et al. (1980)
11. Chameides et al. (1979)
12. Bar Nun (1980)
13. Levine et al. (1982)
14. Lewis (1980)
15. Bar Nun (1975)
16. Borucki et al. (1984)
Reference
1,2,3,4
5,6
6
7, 8, 9, 10
6, 11, 12
11, 12, 13
11
14, 15
14, 15
14, 15
14, 15
14, 15
14, 15
14, 15
14, 15
16
16
16
16
OCR for page 76
76
organic precursor that ultimately led to the chemical
evolution of life on Earth (Miller and Urey, 1959~. Both
laboratory and theoretical calculations indicate that in
a highly reducing atmosphere, rich in hydrocarbons,
lightning could have produced HCN in copious quanti
ties, possibly large enough to allow HCN levels in ponds
and ocean water to build to levels large enough to trig
ger the formation of peptide chains and similar precur
sors to amino acids. On the other hand, the calculations
of Chameides and Walker (1981) indicate that the HCN
yield rapidly decreases as the atmosphere becomes less
reducing. For an atmosphere where C is primarily in the
form of CO, the HCN yield decreases by about 3 orders
of magnitude from that of a hydrocarbon atmosphere,
and it decreases by an additional 3 orders of magnitude
for a COB atmosphere. Thus in order to better under
stand the role of lightning in the evolution of life, studies
are needed to better determine the relative amounts of
CHAD, CO, and CO2 in the primitive atmosphere.
THE POSSIBLE ROLE OF ATMOSPHERIC
DISCHARGES IN CLOUD CHEMISTRY CONCLUSION
In recent years the growing concern over the possible
deleterious effects of acidic precipitation on lakes, forest
ecosystems, and crops has led to an increased interest in
the chemistry of clouds, a region where acids can be effi-
ciently generated and incorporated into rainwater. One
aspect of cloud chemistry that has yet to be adequately
studied is the role of atmospheric electrical phenomena
in acid generation in electrified clouds. One possible ef-
fect of electrical discharges on cloud chemistry is briefly
described below.
Suppose, under the appropriate conditions, continu-
ous, low-level positive point coronal discharges from
droplets occurred in a cloud. These discharges would
cause 1 electron to be deposited on the droplet and 1
positive ion (most often O 2 ~ to be produced in the gas
phase for each ion pair produced (Loeb, 1965~. The
electrons deposited on the droplet would be incorpo-
rated into the droplet and become hydrated electrons
ti.e., (e~)aq]. In the presence of dissolved 02, these hy-
drated electrons would rapidly form O 2 via
(e ja.q + (°2)aq ~ O2. (Reaction6.8)
The O 2 species is related to the aqueous-phase HO2 rad-
ical by the acid-base equilibrium reaction
HO2 ~ - O2 + H+. (Reaction6.9)
REFERENCES
The O 2 ions produced in the gas phase would lead to the
eventual formation of an OH radical and a hydrated
oxonium ion, H3O + (Good et al., 19704. Heterogeneous
scavenging of the H3O + nH2O ion and its incorpora-
tion into the droplets to form H+ would maintain the
WIL`L`lAM L`. CHAMElDES
nominal charge neutrality of the droplets. A sizable
fraction of the gas-phase OH radicals produced by the
discharge would also be scavenged, either as OH or HO2
in the gas phase, and incorporated into the droplet rep-
resenting an additional radical source to the aqueous
phase. Calculations similar to those of Chameides
(1984) indicate that about 1.5 aqueous-phase HO2 free
radicals would be produced for each ion pair generated.
The HO2 radicals thus produced in the aqueous phase
would rapidly react to form dissolved H2O2 via reactions
such as
HO2 + O2 H+' H2O2 + O2 (Reaction6.10)
Since aqueous-phase H2O2 is believed to be, in many
cases, the most important oxidant of dissolved SO2 in
cloud droplets leading to the production of sulfuric acid
(Martin, 1983), it is conceivable that this electrical pro-
cess could play a significant role in the generation of ac-
ids in clouds.
The agreement between theoretical calculations and
experimental determinations of chemical yields from
discharges for a wide range of gaseous species and a wide
range of atmospheres suggests that the basic chemical
mechanism by which trace species are produced by
lightning is fairly well understood. However, in order to
infer global production rates from these chemical yields,
accurate values for the rate at which energy is dissipated
.by lightning is needed. Because these dissipation rates
are not well known (uncertainty factors of 10 for the
Earth and much larger for other planets are estimated),
the role of lightning in the global budgets of species such
as NO remains uncertain. To reduce this uncertainty,
studies are needed to characterize more accurately the
energy and frequency of lightning strokes on a global
scale.
Another area where research is needed concerns coro-
nal discharges and their role as local sources of trace spe-
cies. Mechanisms exist, for instance, by which positive-
point corona from cloud droplets could lead to
enhanced generation of sulfuric acid in cloudwater. To
determine if this and similar processes occur at a signifi-
cant rate, the magnitude of low-level coronal currents
in clouds needs to be more accurately established.
Bar Nun, A. (1975). Thunderstorms on Jupiter, icaTus 24, 86-94.
Bar Nun, A. (1980). Production of nitrogen and carbon species by
thunderstorms on Venus, Icarus 42, 338-342.
Bar Nun, A., and A. Shaviv (1975). Dynamics of the chemical evolu
tion of Earth~s primitive atmosphere, Icarus 24, 197-211.
OCR for page 77
THE ROT Fi OF LIGHTNING IN THE CHEMISTRY OF THE ATMOSPHERE
Borueki, W. L., and W. L. Chameides (1984). Lightning: Estimates
of the rates of energy dissipation and nitrogen fixation, Re?;.
Geophy.s. 22, 364.
Borueki, W. L., C. P. McKay, and R. C. Whitten (1984). Possible
production by lighting of aerosols and trace gases in Titan's atmo-
sphere, Icarus 60, 260-274.
Burns, R. C., and R. W. Hardy (1975). Nitrogen Fixation in Bacteria
and Hig~heTPlant.s, Springer-Verlag, Berlin.
Chameides, W. L. (1979). The implications of CO production in elee-
trieal di.scharge.s, Geophy.s. Re.s. Lett. 6, 287-290.
Chameides, W. L. (1984). The photochemistry of a remote marine
.stratiform cloud, J. Geo phy.s. Re.s. 89, 47-39-47.5.5.
Chameide.s, W. L., and J. C. G. Walker (1981). Rates of fixation by
lightning of carbon and nitrogen in possible primitive atmospheres,
Origins of Life 11.
Chameide.s, W. I,., D. H. Stedman, R. R. Dickerson, D. W. Busch,
and R. J. Cicerone (1977). NOX production in lightning, J. Atmo.s.
Sci..34, 14.~-149.
Chameide.s, W. I,., J. C. G. Walker, and A. F. Nagy (1979). Possible
chemical impact of planetary lightning in the atmospheres of Venus
and Mars, Nature 280, 820-822.
Crutzen, P. J. (198.3). Atmospherie interactions-Homogeneous gas
reactions of C, N. and S containing compounds, in The Major Bio-
~,eochemicc~l Cycles and Their Interactions, B. Bolin and R. B.
Cook, eds., SCOPE, Paris.
Davis, D. D., and W. I,. Chameides (1984). The atmospheric chemis-
try of electrified ck~ud.s, presented at VII International Conference
on Atmospheric Electricity, Albany, N.Y.
Daw.son, C. A. (1980). Nitrogen fixation by lightning, J. Atmo.s. Sci.
.~37, 174-178.
Drapcho, D. I,., D. Sisterson, and R. Kumar (1983). Nitrogen fixation
by lightning activity in a thunderstorm, Atmo.s. Environ. 17, 729-
734.
Calhally, I. E., and C. B. Roy (1978). I,oss of fixed nitrogen from soils
lay nitric oxide exhalation, Nature 275, 734-735.
Good, A., A. Durden, and P. Kebarle (1970). Mechanism and rate
constants of ion-molecule reactions leading to formation of
H- (H2O),, in moist oxygen and air, J. Chem. Phys. 52, 222-229.
Griffing, G. W. (1977). Ozone and oxides of nitrogen during thunder-
storms, J. Geophys. Res. 82, 943-950.
Hill R. D., R. G. Rinker, and H. Die Wilson (1980). Atmospherie
nitrogen fixation by lightning, J. Atmo.s. Sci. 37, 179-192.
I,evine, J. S., R. E. lIughe.s, W. I,. Chameides, and W. E. Howell
( 1979). N O and CO production by electric discharge: Atmospherie
implications, (;c~`,phy.s. Re.s. Lett. 6.
I,evine, J. S., Il. S. Rogow.ski, G. I,. Gregory, W. E. Howell, and J.
Fishman (1.98l). Simultaneous measurements of NOX, NO, and 03
~rr~d~ctir~n in a laboratory di.seharge: Atmospherie implications,
(:e~'phy.s. Ite.s. I,~tt. 8, 357-360.
77
Levine, J. S., G. L. Gregory, G. A. Hershey, W. E. Howell, by. J.
Borueki, and R. E. Orville (1982). Production of nitric oxide by
lightning on Venus, Geophy.s. Re.s. Lett. 9, 893-896.
Levy, H., II, J. D. Mahlman, and W. J. Moxim (1980). Stratospheric
NO!,: A major source of reactive nitrogen in the unpolluted tropo-
sphere, Geophy.s. Res. Lett. 7, 441-444.
I,e~ is, J. S. (1980) . Lightning synthesis of organic compounds on Jupi-
ter, Icarus 42, 85-95.
Lipschultz, F., O. C. Zafirious, S. C. Wofsy, M. B. McElroy, F. W.
Valois, and S. W. Watson (1981). Production of NO and N O by soil
vitrify ing bacteria: A source of atmospheric nitrogen oxides, Nature
294, 641-643.
Loeb, L. B. (1965). Electrical Coronas: Their Basic Physical Mecha-
'`i.sm.s, Univ. of California Press, Berkeley, 694 pp.
I,ogan, J. A. (1983). Nitrogen oxides in the troposphere: Global and
regional budgets, J. Geo phy.s. Res. 88, 10785- 10807.
Logan, J. A., M. J. Prather, S. C. Wofsy, and M. B. McElroy (1981).
Tropospheric chemistry, J. Geophys. Re.s. 86, 7210-7254.
Martin, I,. R. (1983). Kinetic studies of sulfite oxidation in aqueous
solution, in Acicl Precipitation, J. G. Calvert, ea., Ann Arbor Sci-
ence, Ann Arbor, Mich.
McConnell, J. C . (1973) . Atmospheric ammonia, J. Geo phys. Res. 78,
7812-7821.
McFarland, M. C., D. Kley, J. W. Drummond, H. L. Schmeltekopf,
and R. H. Winkler (1979). Nitric oxide measurements in the equato-
rial pacific region, Geophys. Res. Lett. 6, 605-608.
Miller, S. L., and H. C. Urea (1959). Organic compounds synthesis on
the primitive Earth, Science 130, 245-251.
Noxon, J. A. (1976). Atmospheric nitrogen fixation of lightning,
Gcophy.s. Re.s. Lett. 3, 463-465.
Noxon, J. A. (1978). Tropospheric NO, J. Geophy.s. Res. 83, 3051-
3057.
Pet rous, W., and R. M. Lapeyre (1982). Gaseous products created by
electrical discharges in the atmosphere and condensation nuclei re-
.sulting from gaseous phase reactions, Atmo.s. Environ. 16, 959-968.
Picone, J. M., J. P. Boris, J. R. Greig, M. Rayleigh, and R. F. Fernster
(1981). Convective cooling of lightning channels, J. Atmos. Sci. 38,
2056-2062.
Salanave, L. E. (1961). The optical spectrum of lightning, Science
134, 1395-1399.
Sanchez, R. A., J. P. Ferris, and L. E. Orgel (1967). Studies in pre-
hiotic synthesis. II. Synthesis of purine precursors and amino acids
from aqueous hydrogen cyanide, J. Mol. Biol. 30, 223-253.
Tuck, A. F. (1976). Production of nitrogen oxides by lightning dis-
charges, Q. J. R. Meteorol. Soc. 102, 749-755.
Uman, M. A. (1969). Lightning, McGraw-Hill, New York, 264 pp.
Z elovich, Y. B., and Y. P. Raizer (1966). Phy.sic.s of Shock Waves and
High-Temperature Hydrodynamic Phenomena, Academic Press,
New York.
OCR for page 78
OCR for page 79
II
CLOUD AND THUNDERSTORM
ELECTRICITY
OCR for page 80
Representative terms from entire chapter:
trace species
