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The NOxN2O fixation ratio from electrical discharges
Atnwqhcric
End~~unr
CXXU 4981188 S3.00+0.00
Vol. 22, No. 11, pp. 2477..248% 1988.
(3 1988 Pcrgamon Press plc
Printed in Great Britain.
THE NOJN,O
FIXATION RATIO FROM ELECTRICAL DISCHARGES
DONALD
K.
BRANDVOLDand PATRICK MARTINEZ
Chemistry Department, New Mexico Institute of Mining and Technology, Socorro, NM 87801, U.S.A. (First received 18 February 1988 end in ~n~~or~
8 April 1988)
Ahatm&--For energies between 0.005 and 0.1 J, it was observed that NO, (NO + NO& production was approximately linear with electrical discharge energy. This was the case when either the discharge voltage or capacitance was varied. However, N,O production was highly dependent on the discharge conditions (capacitance and voltage). When the discharge capacitance was increased, keeping the discharge voltage constant, N20 production decreased relative to increased discharge energy. When the capacitance was held constant and the discharge voltage varied, the NrO production increased with increased discharge energy. Therefore, different amounts of N,O could be produced from electrical discharges of the same energy. In conclusion, the N,O produced was much less than NO,, however the ratio of the two species was not constant in relation to energy, but depends on the discharge conditions. Key word index: Nitrogen oxides, nitrous oxide, electrical discharges.
I~ODU~ION
The purpose of this research was to examine the NOJN,O ratio produced by electrical discharges as a function of the discharge energy. Laboratory studies regarding NO, production have stated that between 0.25 and 1.25 x lo-’ moles J-’ of NO, were produced (Chameides et al., 197% Levine et aI., 1981; Martinez and Ohline, 1988; Peyrous and Lapeyre, 1982). Levine et al. (1979) reported the N,O production rate as 7 x lo- ‘* moles J- I. They also reported that different discharge energies and multiple discharges gave consistent yields of N20. According to the literature cited, approximately 2 x 10’ times more NO, was produced from equivalent electrical discharges than N,O. EXPERIMENTAL The N,O analyses were performed using a Tracer 550 Gas Chromato~ph equipped with a ‘L3Ni electron capture detector, a Tracer S60 Electron Capture Lmearizer, and a Valco lC+ort valve system equipped with a S.Oml gas ;sampling loop and a pr&olumn. Nttrous oxide samples were analyzed isothermally at 55°C usinn a 12 foot bv 1/84nch (3.6 m x0.32 cm) 0.d: stainless stazi Porapak 6 column (sO/lOOmesh) with a 2-foot pre-column of the same material. The carrier and the make-up gas used for the determinations was 95% Ar/S % CH, which gave better sensitivity than nitrogen. The electrical discharge energies used in this experiment were between 0.005 and 0.1 J. The discharge source was a Wimshurst Generator (Page and Adams, 1969). The discharge energy was varied by placing di5erent capacitors in paralkl with the discharge spheres or by adjusting the dischare voltage by varying the distance between the discharge spheres. The energy per dischatlpc is given by the equation:
where W is the work in joules C is the capacitance in farads V is the voltage in volts. The factor 0.9 is the relative amount of stored energy discharged. This was determined by integrating the work equation between the discharge voltage and the residual voltage (after the discharge). The voltages were measured with a parallel plate held mill meter (Seeker, 1975) and with an electrostatic voltmeter (Singer Metrics, model ENS). The discharge spheres, 1.6 cm in diameter, were enclosed in a Teflon discharge container with a free volume of about 2 ml, Ambient air was drawn into the discharge container from a source several meters removed from the generator since N,O was produced from the plates and the brushes of the generator. The outlet of the discharge container was connected to a 25 ml gas syringe. After a given number of discharges, the syringe was used to draw a sample from the Teflon container. The discharge rate was about 1 s-i. Sample homogeneity was insured by sampling the entire contents of the discharge container. The samples were analyxed immediately after collection. The ambient N,O concentration was about 320 ppb which was determined using N,O standards obtained from Scott Specialty Gases. This value was subtracted from the N?O concentration in the syringe. Given the N,O concentratton in the syringe, the volume of the syringe, the ambient temperature and pressure and the number of discharges, the number of moles of N,O produced from each discharge was determined. The standard deviation of N,,O measurements from the same discharge energy and number of discharges was about 2%. The total NO, produced by electrical discharges was determined by drawing the air exposed to a single discharge from the Teflon discharge container into a Monitor Labs Nitrogen Oxides Analyzer Model 8440. The analyzer was calibrated on the NO and NO, channels with two-tanks of NO (in N,) from Scott Marrin. Standard concentrations were .verit% by the Aeronomy Laboratory of NOAA in Boulder, Colorado. The analyzer was also calibrated on the NO, channel with an NBS NO, permeation tube in conjunction with a calibrated dilution system. From these two methods, the conversion etlickncy was determined to be greater than 95% (Ellis, 1976). A 5.0 ml sample of standard
2477
DONALD
2478
K. BRANDVOLD
and PATRICKMARTINEZ
NO, (in N,) was withdrawn from the output of the permeation tulx mixing chamber and was injected into the intake line of the nitrogen oxides analyzer. From the integrated responseof the injection and the number of moles of NO, in the 5.0 ml sample, the ratio of moles per unit area was determined. The standard deviation of NO, measurements from the same discharge energy was about 5 %. The experimental error for NO, measurements was at most I5 % and was due to uncertainties in the NO, analyzer standardization and in the instrument response measurement.
RESULTS AND DISCUSSION
The NO, formation from ektrical discharges as a function of the discharge energy is shown in Figs 1 and 2. In Fig. 1, the discharge energy was adjusted by changing
the capacitance MOLES
in parallel
OF NO x fX
with the dis-
charge spheres whiie holding constant.
the discharge voltage In Fig. 2, the capacitance was held constant
while the discharge voltage was varied. In both cases a near-linear relationship between the discharge energy and the amount of NO, produced was observed. The NO, formation rate was i.OkO.2 x lo-’ moles J _t which compares well with cited laboratory studies. The N,O analysis was performed by measuring the cumulative effect of several discharges on the air in the discharge container. To determine if each discharge was linearly independent, the number of moles of N,O produced was measured as a function of the number of discharges (Fig. 3). The N,O formation was linear with the number of discharges (at least up to 80 discharges) which indicated that the build-up of NO, in the discharge container was not affecting NzO
10 -’ f
5r
3
21 0
;I
0
ZJ
0
~'.'.'.'~'.'.“"'.J 0.01 0.02 0.03
0.04
DISCHARGE
0.05 ENERGY
0.06
0.07
0.08
0.09
0. 1
(JOULES1
Fig. I. NO, production as a function of the discharge energy. The discharge voltage was 29, Ooo V and the capacitance was varied from 22 to 274 pF.
MU.ES
of
MO,
(X
10.’
)
Fig. 2. NO, production aa a function of the diacharm energy. The capacitance was 154 pF and the discharge voltage was varied from 13,800 to 29,500 V.
NO,/N,O
formation. After 50 discharges, there was a sufficient increase in the NxO concentration above the ambient level for analysis. Next, the N,O formation as a function of discharge energy was examined (Figs 4 and 5). In Fig. 4, the discharge capacitance was held constant and the discharge voltage varied. The graph shows a trend for increased N,O formation with increased discharge energy. In Fig. 5, the discharge capacitance was varied while the discharge voltage was held constant. This was done at two different voltages. The lowest discharge energy, for a given voltage, produced the most N,O. As the discharge energy was increased, the N,O concentration initially decreased and then remained essentially constant.
MOLESOF N20
2479
fixation ratio from ekctrical discharges
Therefore, N,O formation was not a linear function of the discharge energy. Different amounts of N,O could be produced from electrical discharges of the same energy. Nitrous oxide production is thought to occur in the corona column which surrounds a hot discharge channel (Hill et al., 1984). The length of the corona column could affect the amount of N,O produced with a longer column producing more N,O than a shorter column. This may explain the results shown in Fig 4 where N,O production increased with increased discharge distance (voltage). The consistent yields of N,O from different energy discharges observed by Levine et al. (1979) could have been caused by chang-
(X 10 -I0 )
“0
20
ul NlMBER
80
60
im
OF OISCHARCES
Fig. 3. N,O production as a function of the number of discharges. The discharge voltage was 29,500 V and the capacitance was 151 pF, giving a diachargc energy of 0.057 J. Shown is the total amount of N,O produced from the multiple discharges.
MOLES
OF N20
0
(X
10 -I2
0.01
)
0.02 DISCHARGE
0.03 ENERGY
0.04
0.05
0.06
(JOULES)
Fig. 4. N,O production as a function of the discharge energy. The discharge capacitance was 151 pF and the discharge voltage was varied from 15,300 to 28,400 V. A total of 50 discharges was used. Shown is the number of moles of N,O produced from each discharge at a given discharge energy.
2480
DONALD K. BRANDVOLDand PATRICKMAUTINEZ MOLES
OF N20
(X
10 -I*
)
“l-
26.600
v
19.900
v
--*__
t 0’
I
0
0.02
0. 04 OISCHARCE
0.06 ENERGY
0.06
0. 1
0. 12
(JOULES)
Fig. 5. N,O production as a function of the discharge energy. Two discharge voltages were used, 19,800 and 28,600 V. The capacitance was varied from 19 to 274 pF in both cases. A total of 50 discharges was used. Shown is the number of moles of N,O produced from each discharge at a given discharge energy.
ing the discharge distance to increase or decrease the discharge energy. The results in Fig. 5 indicated that N20 production was not directly related to the discharge energy. This implies that a second mechanism besides the corona column may also produce N,O. An electrical discharge begins through an initiation process involving the formation of electrons which excite N2 to the meta-stable N, (A3 Z) state. This species reacts with oxygen to produce N,O (Hill et al., 1984). After the initiation process, channel heating occurs. Some of the species produced during the initiation process are now decomposed in the hot discharge channel. Less decomposition would occur at lower discharge energies because of a smaller volume being heated. This may he the effect shown in Fig. 5. The amount of N,O produced by electrical discharges is equal to the amount from the cold areas of the discharge, both from the initiation process and the corona column surrounding the hot discharge. Acknowledgements-The authors would like to thank Professor C. B. Moore for use of equipment and advice on experimental procedures. Thanks to Edward Franzblau for helping with the NO, measurements and for reviewing this manuscript. Also, thanks to Barbara Romero for helping prepare the manuscript.
REFERENCES
Chameides W. L., Stedman D. H., Dickerson R. R.. Rusch D. W. and Cicerone R. J. (1977) NO, production in lightning. J. afmos. Sci. 34, 143-149. Ellis E. C. (1976) Technical assistance document for the chemiluminesccnce measurement of nitrogen dioxide. EPA-600/4-75-003. Hill R. D.. Rinker R. G. and Coucouvinos A. (1984) Nitrous oxide production by lightning. J. geophys. Res. 89, 141I-1421. Levine J. S., Hughes R. E., Chameides W. L. and Howell W. E. (1979) N,O and CO production by electrical discharges: atmospheric implications. Geophys. Res. Lat. 6, 557-559. Levine J. S., Rogowski R. S., Gregory G. L., Howell W. E. and Fishman J. (1981) Simultaneous measurements of NO,, NO and 0, production in a laboratory discharge: atmospheric i&&cations. Geophys. Res. Ldtt. 8, 3571360. Martinez P. and Ohline R. W. (1988) Investigations into the chemical forms of ekctricall~ fixed nitrog&. Atmospheric Environment 22, 175-t 76. Page L. and Adams N. 1. (1969) Principles of Electricity. pp. 7-9. D. Van Nostrand, Princeton, NJ. Peyrous R. and Lapeyrc R.-M. (1982) Gaseous products created by electrical discharges in the atmosphere and condensation nuclei resulting from gaseous phase reactions. Atmospheric Environment 16, 959-968. Se-cker P. E. (1975) In Sroric Elec?r$cation pp. 173-181, (edited by Blythe A. R.). Inst. Phys. Conf. Ser. No. 27. The Institute of Physics, London.
End~~unr
CXXU 4981188 S3.00+0.00
Vol. 22, No. 11, pp. 2477..248% 1988.
(3 1988 Pcrgamon Press plc
Printed in Great Britain.
THE NOJN,O
FIXATION RATIO FROM ELECTRICAL DISCHARGES
DONALD
K.
BRANDVOLDand PATRICK MARTINEZ
Chemistry Department, New Mexico Institute of Mining and Technology, Socorro, NM 87801, U.S.A. (First received 18 February 1988 end in ~n~~or~
8 April 1988)
Ahatm&--For energies between 0.005 and 0.1 J, it was observed that NO, (NO + NO& production was approximately linear with electrical discharge energy. This was the case when either the discharge voltage or capacitance was varied. However, N,O production was highly dependent on the discharge conditions (capacitance and voltage). When the discharge capacitance was increased, keeping the discharge voltage constant, N20 production decreased relative to increased discharge energy. When the capacitance was held constant and the discharge voltage varied, the NrO production increased with increased discharge energy. Therefore, different amounts of N,O could be produced from electrical discharges of the same energy. In conclusion, the N,O produced was much less than NO,, however the ratio of the two species was not constant in relation to energy, but depends on the discharge conditions. Key word index: Nitrogen oxides, nitrous oxide, electrical discharges.
I~ODU~ION
The purpose of this research was to examine the NOJN,O ratio produced by electrical discharges as a function of the discharge energy. Laboratory studies regarding NO, production have stated that between 0.25 and 1.25 x lo-’ moles J-’ of NO, were produced (Chameides et al., 197% Levine et aI., 1981; Martinez and Ohline, 1988; Peyrous and Lapeyre, 1982). Levine et al. (1979) reported the N,O production rate as 7 x lo- ‘* moles J- I. They also reported that different discharge energies and multiple discharges gave consistent yields of N20. According to the literature cited, approximately 2 x 10’ times more NO, was produced from equivalent electrical discharges than N,O. EXPERIMENTAL The N,O analyses were performed using a Tracer 550 Gas Chromato~ph equipped with a ‘L3Ni electron capture detector, a Tracer S60 Electron Capture Lmearizer, and a Valco lC+ort valve system equipped with a S.Oml gas ;sampling loop and a pr&olumn. Nttrous oxide samples were analyzed isothermally at 55°C usinn a 12 foot bv 1/84nch (3.6 m x0.32 cm) 0.d: stainless stazi Porapak 6 column (sO/lOOmesh) with a 2-foot pre-column of the same material. The carrier and the make-up gas used for the determinations was 95% Ar/S % CH, which gave better sensitivity than nitrogen. The electrical discharge energies used in this experiment were between 0.005 and 0.1 J. The discharge source was a Wimshurst Generator (Page and Adams, 1969). The discharge energy was varied by placing di5erent capacitors in paralkl with the discharge spheres or by adjusting the dischare voltage by varying the distance between the discharge spheres. The energy per dischatlpc is given by the equation:
where W is the work in joules C is the capacitance in farads V is the voltage in volts. The factor 0.9 is the relative amount of stored energy discharged. This was determined by integrating the work equation between the discharge voltage and the residual voltage (after the discharge). The voltages were measured with a parallel plate held mill meter (Seeker, 1975) and with an electrostatic voltmeter (Singer Metrics, model ENS). The discharge spheres, 1.6 cm in diameter, were enclosed in a Teflon discharge container with a free volume of about 2 ml, Ambient air was drawn into the discharge container from a source several meters removed from the generator since N,O was produced from the plates and the brushes of the generator. The outlet of the discharge container was connected to a 25 ml gas syringe. After a given number of discharges, the syringe was used to draw a sample from the Teflon container. The discharge rate was about 1 s-i. Sample homogeneity was insured by sampling the entire contents of the discharge container. The samples were analyxed immediately after collection. The ambient N,O concentration was about 320 ppb which was determined using N,O standards obtained from Scott Specialty Gases. This value was subtracted from the N?O concentration in the syringe. Given the N,O concentratton in the syringe, the volume of the syringe, the ambient temperature and pressure and the number of discharges, the number of moles of N,O produced from each discharge was determined. The standard deviation of N,,O measurements from the same discharge energy and number of discharges was about 2%. The total NO, produced by electrical discharges was determined by drawing the air exposed to a single discharge from the Teflon discharge container into a Monitor Labs Nitrogen Oxides Analyzer Model 8440. The analyzer was calibrated on the NO and NO, channels with two-tanks of NO (in N,) from Scott Marrin. Standard concentrations were .verit% by the Aeronomy Laboratory of NOAA in Boulder, Colorado. The analyzer was also calibrated on the NO, channel with an NBS NO, permeation tube in conjunction with a calibrated dilution system. From these two methods, the conversion etlickncy was determined to be greater than 95% (Ellis, 1976). A 5.0 ml sample of standard
2477
DONALD
2478
K. BRANDVOLD
and PATRICKMARTINEZ
NO, (in N,) was withdrawn from the output of the permeation tulx mixing chamber and was injected into the intake line of the nitrogen oxides analyzer. From the integrated responseof the injection and the number of moles of NO, in the 5.0 ml sample, the ratio of moles per unit area was determined. The standard deviation of NO, measurements from the same discharge energy was about 5 %. The experimental error for NO, measurements was at most I5 % and was due to uncertainties in the NO, analyzer standardization and in the instrument response measurement.
RESULTS AND DISCUSSION
The NO, formation from ektrical discharges as a function of the discharge energy is shown in Figs 1 and 2. In Fig. 1, the discharge energy was adjusted by changing
the capacitance MOLES
in parallel
OF NO x fX
with the dis-
charge spheres whiie holding constant.
the discharge voltage In Fig. 2, the capacitance was held constant
while the discharge voltage was varied. In both cases a near-linear relationship between the discharge energy and the amount of NO, produced was observed. The NO, formation rate was i.OkO.2 x lo-’ moles J _t which compares well with cited laboratory studies. The N,O analysis was performed by measuring the cumulative effect of several discharges on the air in the discharge container. To determine if each discharge was linearly independent, the number of moles of N,O produced was measured as a function of the number of discharges (Fig. 3). The N,O formation was linear with the number of discharges (at least up to 80 discharges) which indicated that the build-up of NO, in the discharge container was not affecting NzO
10 -’ f
5r
3
21 0
;I
0
ZJ
0
~'.'.'.'~'.'.“"'.J 0.01 0.02 0.03
0.04
DISCHARGE
0.05 ENERGY
0.06
0.07
0.08
0.09
0. 1
(JOULES1
Fig. I. NO, production as a function of the discharge energy. The discharge voltage was 29, Ooo V and the capacitance was varied from 22 to 274 pF.
MU.ES
of
MO,
(X
10.’
)
Fig. 2. NO, production aa a function of the diacharm energy. The capacitance was 154 pF and the discharge voltage was varied from 13,800 to 29,500 V.
NO,/N,O
formation. After 50 discharges, there was a sufficient increase in the NxO concentration above the ambient level for analysis. Next, the N,O formation as a function of discharge energy was examined (Figs 4 and 5). In Fig. 4, the discharge capacitance was held constant and the discharge voltage varied. The graph shows a trend for increased N,O formation with increased discharge energy. In Fig. 5, the discharge capacitance was varied while the discharge voltage was held constant. This was done at two different voltages. The lowest discharge energy, for a given voltage, produced the most N,O. As the discharge energy was increased, the N,O concentration initially decreased and then remained essentially constant.
MOLESOF N20
2479
fixation ratio from ekctrical discharges
Therefore, N,O formation was not a linear function of the discharge energy. Different amounts of N,O could be produced from electrical discharges of the same energy. Nitrous oxide production is thought to occur in the corona column which surrounds a hot discharge channel (Hill et al., 1984). The length of the corona column could affect the amount of N,O produced with a longer column producing more N,O than a shorter column. This may explain the results shown in Fig 4 where N,O production increased with increased discharge distance (voltage). The consistent yields of N,O from different energy discharges observed by Levine et al. (1979) could have been caused by chang-
(X 10 -I0 )
“0
20
ul NlMBER
80
60
im
OF OISCHARCES
Fig. 3. N,O production as a function of the number of discharges. The discharge voltage was 29,500 V and the capacitance was 151 pF, giving a diachargc energy of 0.057 J. Shown is the total amount of N,O produced from the multiple discharges.
MOLES
OF N20
0
(X
10 -I2
0.01
)
0.02 DISCHARGE
0.03 ENERGY
0.04
0.05
0.06
(JOULES)
Fig. 4. N,O production as a function of the discharge energy. The discharge capacitance was 151 pF and the discharge voltage was varied from 15,300 to 28,400 V. A total of 50 discharges was used. Shown is the number of moles of N,O produced from each discharge at a given discharge energy.
2480
DONALD K. BRANDVOLDand PATRICKMAUTINEZ MOLES
OF N20
(X
10 -I*
)
“l-
26.600
v
19.900
v
--*__
t 0’
I
0
0.02
0. 04 OISCHARCE
0.06 ENERGY
0.06
0. 1
0. 12
(JOULES)
Fig. 5. N,O production as a function of the discharge energy. Two discharge voltages were used, 19,800 and 28,600 V. The capacitance was varied from 19 to 274 pF in both cases. A total of 50 discharges was used. Shown is the number of moles of N,O produced from each discharge at a given discharge energy.
ing the discharge distance to increase or decrease the discharge energy. The results in Fig. 5 indicated that N20 production was not directly related to the discharge energy. This implies that a second mechanism besides the corona column may also produce N,O. An electrical discharge begins through an initiation process involving the formation of electrons which excite N2 to the meta-stable N, (A3 Z) state. This species reacts with oxygen to produce N,O (Hill et al., 1984). After the initiation process, channel heating occurs. Some of the species produced during the initiation process are now decomposed in the hot discharge channel. Less decomposition would occur at lower discharge energies because of a smaller volume being heated. This may he the effect shown in Fig. 5. The amount of N,O produced by electrical discharges is equal to the amount from the cold areas of the discharge, both from the initiation process and the corona column surrounding the hot discharge. Acknowledgements-The authors would like to thank Professor C. B. Moore for use of equipment and advice on experimental procedures. Thanks to Edward Franzblau for helping with the NO, measurements and for reviewing this manuscript. Also, thanks to Barbara Romero for helping prepare the manuscript.
REFERENCES
Chameides W. L., Stedman D. H., Dickerson R. R.. Rusch D. W. and Cicerone R. J. (1977) NO, production in lightning. J. afmos. Sci. 34, 143-149. Ellis E. C. (1976) Technical assistance document for the chemiluminesccnce measurement of nitrogen dioxide. EPA-600/4-75-003. Hill R. D.. Rinker R. G. and Coucouvinos A. (1984) Nitrous oxide production by lightning. J. geophys. Res. 89, 141I-1421. Levine J. S., Hughes R. E., Chameides W. L. and Howell W. E. (1979) N,O and CO production by electrical discharges: atmospheric implications. Geophys. Res. Lat. 6, 557-559. Levine J. S., Rogowski R. S., Gregory G. L., Howell W. E. and Fishman J. (1981) Simultaneous measurements of NO,, NO and 0, production in a laboratory discharge: atmospheric i&&cations. Geophys. Res. Ldtt. 8, 3571360. Martinez P. and Ohline R. W. (1988) Investigations into the chemical forms of ekctricall~ fixed nitrog&. Atmospheric Environment 22, 175-t 76. Page L. and Adams N. 1. (1969) Principles of Electricity. pp. 7-9. D. Van Nostrand, Princeton, NJ. Peyrous R. and Lapeyrc R.-M. (1982) Gaseous products created by electrical discharges in the atmosphere and condensation nuclei resulting from gaseous phase reactions. Atmospheric Environment 16, 959-968. Se-cker P. E. (1975) In Sroric Elec?r$cation pp. 173-181, (edited by Blythe A. R.). Inst. Phys. Conf. Ser. No. 27. The Institute of Physics, London.