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Implications for atmospheric negative ion composition measurements of laboratory ECA studies of sulfuric acid cluster ions
Planet. Printed
Space Sci., Vol. 34, No. 2, pp. 245.252, in Great Britain.
1986.
0032-0633186 $3.CKl+O.tM Pergamon Press Ltd.
SHORT PAPERS IMPLICATIONS FOR ATWW’HERIC NEGATIVE IDN COMPOSITION MEASUREMENTS OF LABORATORY ECA STUDIES OF SULFURIC ACID CLUSTER IONS
ii. Schlager
Postfach
and F. Arnold
Max-Planck-Institut fiir Kernphysik 103 908, D-6900 Heidelberg, F.R. Germany (Received
22 November
1985)
ABSTRACT Laboratory studies of electric field-induced collisional activation (ECA) of HSO;(H$04), cluster ions were made revealing fragmentation via two channels: HSOi + H2S04 and HSO,SO, + H20. This result suggests that mixed cluster ions of the type HSO;(H2S04)1 X with X having a mass of 8121 amu which were recently detected in the stratosphere may not represent true ambient ions but are fragments formed by ECA of ambient HSOi(H2S04), clusters during ion sampling into the mass spectrometer. Implications for stratospheric negative ion composition measurements are discussed. INTRODUCTION Electric field-induced collisional activation (ECA)' of ions may cause severe ion fragmentation problems in atmospheric ion composition measurements using pumped mass spectrometers. In these experiments ECA is induced by electric fields employed for extraction of ions from the gas jet forming behind the inlet orifice of the mass spectrometer. Apart from being a disturbing effect, however, ion fragmentation by ECA may also serve as a powerful tool for composition and structure analysis of ion species particularly ones with large mass numbers. Mainly due to this application, ECA has recently attained increasing interest which has initiated various laboratory ECA studies involving ions of atmospheric interest (Knop and Arnold, 1985; Schlager and Arnold, 1985a; Schlager and Arnold, 1985b). The present paper reports on the first laboratory ECA studies of HSO~(H$04), cluster ions which represent the most abundant atmospheric negative ions between about 25 km and 50 km and which were originally detected by Arnold and Henschen (1978). More recently, improved balloon-borne mass spectrometers with larger mass resolution and sensitivity have detected small mass peaks accompanying the mass peaks of the HSOi(H$04), clusters and having mass numbers, which are smaller by 1721 amu (atomic mass units).relative to the mass numbers of the HSO~(HZSO~)~ clusters (Arnold et al., 1982; Qiu and Arnold, 1984). It was hypothesized by these authors that the newly detected ion species may represent mixed clusters of the type HSOi(H2S04)lHS03 and that these may be formed in the stratosphere by attachment of HS03 radicals. An alternative possibility that these ions being HSO,(H,SO,)lSO3 clusters seemed to be unlikely, as pointed out by these authors, since the abundance of stratospheric SO3 is expected to be very low as SO3 reacts quickly with HZ0 leading to H2S04 (Holland and Castleman, 1978). Recent laboratory measurements of Stockwell and Calvert (1983), however, showed that HS03 reacts quickly with 02 leading to SO3 and HO2 which implies that HS03 should also not reach a significant abundance in the stratosphere and therefore should not influence the negative ions.
246
Short Paper
In order to resolve the nature of the newly detected stratospheric negative ions HSOi(H2S04),X with X having mass 8151 amu, the present paper investigates the possibility these ions may represent fragments formed by ECA. EXPERIMENTAL
METHOD
The experimental method used for the present studies is similar to the ones used in previous studies of ECA and ion-molecule reactions carried out by our group (Schlager et al., 1983; Glebe and Arnold, 1983; Knop and Arnold, 1985; Schlager and Arnold, 1985a; Schlager and Arnold, 1985b) and will therefore only briefly reviewed here. It employs an ion drift cell apparatus (Fig. l), which consists of three major elements: an ion drift cell, a high pressure glow discharge ion source, and a quadrupole mass spectrometer.
DI P
r TMP I
Figure
1: Schematic illustration of the ion drift-cell apparatus. IS: Ion source, DE: Discharge electrodes, SI: Source gas inlet, El: Ion source extraction electrode, E2: Ion shutter, 0: Drift-cell, FP: Front plate, RP: Rear plate, DI: Drift-cell gas inlet, P: Pressure gauge port, QMS: Quadrupole mass spectrometer, CEM: Channeltron, TMP: Turbomolecular pump.
that
Short Paper
247
Cluster ions of the type HSOi(H2S04), are formed in the ionsource using a gas mixture of air, water vapour and SO*. After leaving the ion source chamber via an exit hole drilled into the planar extraction electrode (diameter: 0.03 cm) primary ions are gently injected into the ion drift cell via an inlet hole (diameter: 0.1 cm) drilled into the front electrode of the drift cell. The cylindrical drift cell has a length of 2.45 cm and In order to is filled with argon (pressure: 0.08 Torr) serving as an inert buffer gas. avoid severe ion fragmentation during injection the front electrode of the drift cell is kept at a very small attractive potential (usually less than 1 V) relative to the extraction electrode of the ion source chamber. After injection the ions traverse the cell in a drift motion imposed by a nearly uniform electric field (strength E) between the front and rear electrodes. Mass analysis of the ions leaving the drift cell via an exit hole (diameter: 0.05 cm) is provided by a quadrupole mass spectrometer with a channeltron detector. By raising E increasing internal ion excitation can be induced and the "hot" ions undergo increasing fragmentation. RESULTS
AN0 DISCUSSION
Figure 2 shows mass spectra of ions leaving the drift cell for low (a; 4.1 V cm-I), medium (b; 8.2 V cm-I), and high (c; 16.3 V cm-l) drift field E. For low E HSO,(H2SO4) (195) is most abundant, for medium E the fragment HS04 (97) becomes most abundant while some HSO;;SO, (177) becomes also noticeable (expanded part of Figure 2b) and for high E the fragments HSOi (97), SOS (80), and OH- (17) are most abundant. Figure 3 shows
the variation
of fractional
count rates for ion species
leaving
the
drift cell with increasing E. As E is raised, the most abundant injected ions HSO~(H~SO4) (195) and HSO~(H~SO4)~ (293) decrease quickly due to fragmentation while the fragment HSOi (97) increases. At larger E even HSP; decomposes and the secondary fragments are SOi (80) and OH- (17). Interestingly, an additional fragment namely HSOiSO3 (177) is formed at E values around 7 to 9 V cm- where HSOiH2S04 is still abundant. Therefore it appears that ECA of HSOi H~SOQ which decomposes via two channels: (HSO~H~SO4)*
leads to an excited
--> HSO; + H2S04
(la)
--> HSO,SO,
(lb)
i Hz0
complex
(HSOiH2S04)*
and that HSO;IS03, in turn, is lost by ECA leading to HSO;. The maximum abundance ratio reached for HSO,SO, and HSOgH2S04 is around 0.1. The measurements also imply that SO3 bonds relatively strongly to HSO;j. Interestingly, the energy required to fragment H~SOJ into SO3 and Hz0 (about 23 kcal/mol; Holland and Castleman, 1978) is only slightly larger than the estimated lower limit to the strength of the HSOi-H2S04 bond (> 22 kcal/mol; Arnold and Qiu, 1984). Thus, the efficiency of channel (lb) can be significant compared to (la) as in fact indicated in the present studies. In this regard, the cluster ions HS0i(H2S04)n seem to be exceptional. The branching ratio for the two decomposition channels (la) and (lb) is difficult to estimate from our measurements as the efficiency for ECA-induced fragmentation of HSO,SO, is not known. The present data give a lower limit of about one percent to the fractional production of HSO$03 via process (lb). The maximum
abundance
ratio for HSO$O,
and HSO;H$04
of 0-I as measured
in our
laboratory studies may be compared to the abundance ratios for HSO~(H*S04)n_~x and HSO;j (~zSO4)n with n equal to two (275/293) and three (3731391) as observed in ion composition ~asurements on two balloon flights of our group (Figure 4). These abundance ratios range between about 0.03 and 0.5 with a tendency towards higher values at lower altitudes and
248
are,
Short Paper
thus,
measured
of the same order as the maximum in our laboratory experiment. 4.800
j
I
abundance
I
ratio for HSOiSO3
I_
I
%
a I
(a)
-% rl F
3.600 -
2.400
and HSOiH2S04
-
4000 a (b)
3000-
moo
-
1200 8 Cc) 900-
6Oo-
8
300 $ 09-..!
.“V
. . . . 100
..:... 200
MASS Figure 2:
;
.: 300
I....: 400
(A.M.U.)
Mass spectra of negative ions leaving the drift cell for low (a), medium (b), and high (c) drift field E. Mass numbers are given (17: 195: HSOiH2S04; 293: HSOi OH-; 80: SOj; 97: HSO;; 177: HS0$03; (H2SO4)2).
ShortPaper
249
Pressure
2931
0.1
’
’
’
’
1 ’ 5
177
f ’
’
The a change pressure the mass
3:
Torr
Ar
A
’
1 ’
10
’
3
’
Field StrenQth ( Volt/cm
Figure
0.08
’
1 ’
15
’
’
’
1 ’
20
)
Fractional abundances of negative ions as a function of the electric field strength in the drift cell. Ion mass numbers are given (see Fig.2). Arrows indicate upper limits.
increase of the ion abundance ratios (Figure 4) at the lower heights may reflect in the ECA conditions for the atmospheric ions with increasing ambient gas due to an increasing intenseness of the gas jet forming behind the inlet hole of spectrometer.
Very recently, in-situ ECA studies of negative cluster ions have been performed by our group during ion composition measurements in the stratosphere using a mass spectrometer probe equipped with an ECA chamber (these data will be reported in a separate paper). The measurements revealed that mixed HS0,(H2S04)l(HN03)m cluster ions have a similar fragmentation behaviour as observed in the laboratory studies forHSOi(H2S04), cluster ions. For example, ECA of HSO;jHN03 involves two fragmentation channels (HSO;HN03)*
--> HSOZ + HNO3
(2a)
--> (N03S03)-
(2b)
+ H20
250
Short Paper
This indicates that, in addition to the cluster ions of the type HSO,(H2SO4)T X with X having a mass of 8151 amu also various other minor negative cluster ions which were detected in the stratosphere may represent fragments formed during ion sampling. A compilation of observed mass numbers for minor negative ions in ion composition measurements which may represent fragment ions is given in Table 1 along with previous tentative identifications.
Table 1:
Mass numbers
of minor
stratospheric
negative
ions which
may r2ptTSent
fragment
ions.
Mass in amu
Previous tentative identification
8022
NOjH20
9122
NOjHCl,
Possible
Ref.
fragment
so; HSO;i
HSOi 1
14321
~~~~~3H20 3 3
14422
NOjHN03H20
17822
HSO~HN03H20 HS0,HS03
17922
HS0,HN03H20 NOjHNO3HOCl
20522
NOj(HN03)2H20
(No,SO,)-HN03
24121
HSO~'(HN03) H20 HSO~HN03HS 6 3
(NO,SO,)-H2S04
27522
HSOqH2S04HN03H20
27621
HSO~H2S04HS03
37421
HSOi(H2S04)2HS03
(1) Arnold and Qiu (1984) (2) Arijs et al. (1982)
(NQjSO3)-
1
ttso;so3
.I
I
tiSO,(H2SO4)SO3
HSOq(H2S04)2S03
ion
251
Short Paper
38
32
30 0.0 1
I
I
I
t Illill
I
I I I IlId 1
0.1
ION RATIO
Figure 4:
Abundance ratios for HSOq(H2S04)n_TX and HS0i(H2S04)n cluster ions with n equal to two (275/293) and three (373/391) as observed in two balloon-borne ion composition measurements.
CONCLUSIONS The present laboratory ECA studies show that ECA of HSOjH2SO4 leads to the formation of HSOiSO3 besides HSOi. Considering this result, it is conceivable that the mixed cluster ions of the type HSO~(H*SO4)~X with X having a mass of 8151 amu which were recently observed in balloon-borne ion composition measurements in the stratosphere do not represent true ambient ions but are fragments formed by ECA of ambient HS0i(H2S04)n clusters during ion sampling into the mass probes for stratospheric HS03 or SO3.
spectrometer.
If
so,
these ions cannot
serve as
Recent in-situ ECA studies revealed that ECA of mixed HSO,(H2SO4),(HNO3), clusters involves also additional fragmentation channels resulting in fragment ions which may be misinterpreted as ambient ions in ion composition measurements.
252
ShortPaper
ACKNOWLEDGEMENTS The authors wish to express their thanks to E. Ferguson and A.A. Viggiano for stimulating discussions. Support by the technical staffs of the Max-Planck-Institut fir Kernphysik and the balloon group of the Centre National d-Etudes Spatiales at Aire-surl‘Adour, France is gratefully appreciated. This work was supported in part by the Bundesministerium fUr Forschung und Technologie through Gesellschaft fiir Strahlen- und Umweltforschung. REFERENCES Arijs,
E., Nevejans, D., Frederick, P. and Ingels, J.(1982). Stratospheric negative composition measurements, ion abundances and related trace gas detection. J.Atmos.Terr.Phys. 44, 681.
Arnold, F. and Henschen, Nature 275, 521.
G. (1978). First
mass
analysis
of stratospheric
negative
ion
ions.
Arnold, F., Viggiano, A.A. and Schlager, H.(1982). Implications for trace gases and aerosols of large negative ion clusters in the stratosphere. Nature 297, 371. Arnold, F. and Qiu, S. (1984). Upper stratosphere negative ion composition and inferred trace gas abundances. Planet. Space Sci. 32, 169.
measurements
Glebe, W. and Arnold, F. (1983). Negative acid cluster ion hydration studies of atmospheric interest. Proc.Intern. Swarm Seminar, Innsbruck, Austria 1983, 132. Holland, P.M. and Castleman, A.W. (1978). Gas phase complexes: Considerations of the stability of clusters in the sulfurtrioxide-water system. Chem.Phys.Lett. 56, 511. Knop, G. and Arnold, F. (1985). Acetone measurements in the upper troposphere stratosphere. Planet. Space Sci. (to be published).
and lower
Qiu, S. and Arnold, F. (1984). Stratospheric in situ measurements of H2SO4 and HS03 vapors during a volcanically active period. Planet. Space Sci. 32, 87. Schlager, H., Fabian, R. and Arnold, F.(1983).A new cluster ion source/ion drift cell apparatus for atmospheric ion studies - First mobility and reaction rate coefficient measurements. Proc.Intern. Swarm Seminar, Innsbruck, Austria 1983, 257. Schlager, H. and Arnold, F. (1985a). Balloon-borne of stratospheric positive ions: Unambiguous Planet.
fragment detection
ion mass
spectrometry
Space Sci. (submitted).
Schlager, H. and Arnold, F. (1985b). Acetonitrile in the stratosphere - Unambiguous identification using fragment ion mass spectrometry (to be published). Stockwell, W.R. and Calvert, J.G. (1983). The mechanism Atmos.Environ. 17, 2331.
studies
of H+(CHCN)l(H20),-clusters.
of the HO-SO2
reaction.
Space Sci., Vol. 34, No. 2, pp. 245.252, in Great Britain.
1986.
0032-0633186 $3.CKl+O.tM Pergamon Press Ltd.
SHORT PAPERS IMPLICATIONS FOR ATWW’HERIC NEGATIVE IDN COMPOSITION MEASUREMENTS OF LABORATORY ECA STUDIES OF SULFURIC ACID CLUSTER IONS
ii. Schlager
Postfach
and F. Arnold
Max-Planck-Institut fiir Kernphysik 103 908, D-6900 Heidelberg, F.R. Germany (Received
22 November
1985)
ABSTRACT Laboratory studies of electric field-induced collisional activation (ECA) of HSO;(H$04), cluster ions were made revealing fragmentation via two channels: HSOi + H2S04 and HSO,SO, + H20. This result suggests that mixed cluster ions of the type HSO;(H2S04)1 X with X having a mass of 8121 amu which were recently detected in the stratosphere may not represent true ambient ions but are fragments formed by ECA of ambient HSOi(H2S04), clusters during ion sampling into the mass spectrometer. Implications for stratospheric negative ion composition measurements are discussed. INTRODUCTION Electric field-induced collisional activation (ECA)' of ions may cause severe ion fragmentation problems in atmospheric ion composition measurements using pumped mass spectrometers. In these experiments ECA is induced by electric fields employed for extraction of ions from the gas jet forming behind the inlet orifice of the mass spectrometer. Apart from being a disturbing effect, however, ion fragmentation by ECA may also serve as a powerful tool for composition and structure analysis of ion species particularly ones with large mass numbers. Mainly due to this application, ECA has recently attained increasing interest which has initiated various laboratory ECA studies involving ions of atmospheric interest (Knop and Arnold, 1985; Schlager and Arnold, 1985a; Schlager and Arnold, 1985b). The present paper reports on the first laboratory ECA studies of HSO~(H$04), cluster ions which represent the most abundant atmospheric negative ions between about 25 km and 50 km and which were originally detected by Arnold and Henschen (1978). More recently, improved balloon-borne mass spectrometers with larger mass resolution and sensitivity have detected small mass peaks accompanying the mass peaks of the HSOi(H$04), clusters and having mass numbers, which are smaller by 1721 amu (atomic mass units).relative to the mass numbers of the HSO~(HZSO~)~ clusters (Arnold et al., 1982; Qiu and Arnold, 1984). It was hypothesized by these authors that the newly detected ion species may represent mixed clusters of the type HSOi(H2S04)lHS03 and that these may be formed in the stratosphere by attachment of HS03 radicals. An alternative possibility that these ions being HSO,(H,SO,)lSO3 clusters seemed to be unlikely, as pointed out by these authors, since the abundance of stratospheric SO3 is expected to be very low as SO3 reacts quickly with HZ0 leading to H2S04 (Holland and Castleman, 1978). Recent laboratory measurements of Stockwell and Calvert (1983), however, showed that HS03 reacts quickly with 02 leading to SO3 and HO2 which implies that HS03 should also not reach a significant abundance in the stratosphere and therefore should not influence the negative ions.
246
Short Paper
In order to resolve the nature of the newly detected stratospheric negative ions HSOi(H2S04),X with X having mass 8151 amu, the present paper investigates the possibility these ions may represent fragments formed by ECA. EXPERIMENTAL
METHOD
The experimental method used for the present studies is similar to the ones used in previous studies of ECA and ion-molecule reactions carried out by our group (Schlager et al., 1983; Glebe and Arnold, 1983; Knop and Arnold, 1985; Schlager and Arnold, 1985a; Schlager and Arnold, 1985b) and will therefore only briefly reviewed here. It employs an ion drift cell apparatus (Fig. l), which consists of three major elements: an ion drift cell, a high pressure glow discharge ion source, and a quadrupole mass spectrometer.
DI P
r TMP I
Figure
1: Schematic illustration of the ion drift-cell apparatus. IS: Ion source, DE: Discharge electrodes, SI: Source gas inlet, El: Ion source extraction electrode, E2: Ion shutter, 0: Drift-cell, FP: Front plate, RP: Rear plate, DI: Drift-cell gas inlet, P: Pressure gauge port, QMS: Quadrupole mass spectrometer, CEM: Channeltron, TMP: Turbomolecular pump.
that
Short Paper
247
Cluster ions of the type HSOi(H2S04), are formed in the ionsource using a gas mixture of air, water vapour and SO*. After leaving the ion source chamber via an exit hole drilled into the planar extraction electrode (diameter: 0.03 cm) primary ions are gently injected into the ion drift cell via an inlet hole (diameter: 0.1 cm) drilled into the front electrode of the drift cell. The cylindrical drift cell has a length of 2.45 cm and In order to is filled with argon (pressure: 0.08 Torr) serving as an inert buffer gas. avoid severe ion fragmentation during injection the front electrode of the drift cell is kept at a very small attractive potential (usually less than 1 V) relative to the extraction electrode of the ion source chamber. After injection the ions traverse the cell in a drift motion imposed by a nearly uniform electric field (strength E) between the front and rear electrodes. Mass analysis of the ions leaving the drift cell via an exit hole (diameter: 0.05 cm) is provided by a quadrupole mass spectrometer with a channeltron detector. By raising E increasing internal ion excitation can be induced and the "hot" ions undergo increasing fragmentation. RESULTS
AN0 DISCUSSION
Figure 2 shows mass spectra of ions leaving the drift cell for low (a; 4.1 V cm-I), medium (b; 8.2 V cm-I), and high (c; 16.3 V cm-l) drift field E. For low E HSO,(H2SO4) (195) is most abundant, for medium E the fragment HS04 (97) becomes most abundant while some HSO;;SO, (177) becomes also noticeable (expanded part of Figure 2b) and for high E the fragments HSOi (97), SOS (80), and OH- (17) are most abundant. Figure 3 shows
the variation
of fractional
count rates for ion species
leaving
the
drift cell with increasing E. As E is raised, the most abundant injected ions HSO~(H~SO4) (195) and HSO~(H~SO4)~ (293) decrease quickly due to fragmentation while the fragment HSOi (97) increases. At larger E even HSP; decomposes and the secondary fragments are SOi (80) and OH- (17). Interestingly, an additional fragment namely HSOiSO3 (177) is formed at E values around 7 to 9 V cm- where HSOiH2S04 is still abundant. Therefore it appears that ECA of HSOi H~SOQ which decomposes via two channels: (HSO~H~SO4)*
leads to an excited
--> HSO; + H2S04
(la)
--> HSO,SO,
(lb)
i Hz0
complex
(HSOiH2S04)*
and that HSO;IS03, in turn, is lost by ECA leading to HSO;. The maximum abundance ratio reached for HSO,SO, and HSOgH2S04 is around 0.1. The measurements also imply that SO3 bonds relatively strongly to HSO;j. Interestingly, the energy required to fragment H~SOJ into SO3 and Hz0 (about 23 kcal/mol; Holland and Castleman, 1978) is only slightly larger than the estimated lower limit to the strength of the HSOi-H2S04 bond (> 22 kcal/mol; Arnold and Qiu, 1984). Thus, the efficiency of channel (lb) can be significant compared to (la) as in fact indicated in the present studies. In this regard, the cluster ions HS0i(H2S04)n seem to be exceptional. The branching ratio for the two decomposition channels (la) and (lb) is difficult to estimate from our measurements as the efficiency for ECA-induced fragmentation of HSO,SO, is not known. The present data give a lower limit of about one percent to the fractional production of HSO$03 via process (lb). The maximum
abundance
ratio for HSO$O,
and HSO;H$04
of 0-I as measured
in our
laboratory studies may be compared to the abundance ratios for HSO~(H*S04)n_~x and HSO;j (~zSO4)n with n equal to two (275/293) and three (3731391) as observed in ion composition ~asurements on two balloon flights of our group (Figure 4). These abundance ratios range between about 0.03 and 0.5 with a tendency towards higher values at lower altitudes and
248
are,
Short Paper
thus,
measured
of the same order as the maximum in our laboratory experiment. 4.800
j
I
abundance
I
ratio for HSOiSO3
I_
I
%
a I
(a)
-% rl F
3.600 -
2.400
and HSOiH2S04
-
4000 a (b)
3000-
moo
-
1200 8 Cc) 900-
6Oo-
8
300 $ 09-..!
.“V
. . . . 100
..:... 200
MASS Figure 2:
;
.: 300
I....: 400
(A.M.U.)
Mass spectra of negative ions leaving the drift cell for low (a), medium (b), and high (c) drift field E. Mass numbers are given (17: 195: HSOiH2S04; 293: HSOi OH-; 80: SOj; 97: HSO;; 177: HS0$03; (H2SO4)2).
ShortPaper
249
Pressure
2931
0.1
’
’
’
’
1 ’ 5
177
f ’
’
The a change pressure the mass
3:
Torr
Ar
A
’
1 ’
10
’
3
’
Field StrenQth ( Volt/cm
Figure
0.08
’
1 ’
15
’
’
’
1 ’
20
)
Fractional abundances of negative ions as a function of the electric field strength in the drift cell. Ion mass numbers are given (see Fig.2). Arrows indicate upper limits.
increase of the ion abundance ratios (Figure 4) at the lower heights may reflect in the ECA conditions for the atmospheric ions with increasing ambient gas due to an increasing intenseness of the gas jet forming behind the inlet hole of spectrometer.
Very recently, in-situ ECA studies of negative cluster ions have been performed by our group during ion composition measurements in the stratosphere using a mass spectrometer probe equipped with an ECA chamber (these data will be reported in a separate paper). The measurements revealed that mixed HS0,(H2S04)l(HN03)m cluster ions have a similar fragmentation behaviour as observed in the laboratory studies forHSOi(H2S04), cluster ions. For example, ECA of HSO;jHN03 involves two fragmentation channels (HSO;HN03)*
--> HSOZ + HNO3
(2a)
--> (N03S03)-
(2b)
+ H20
250
Short Paper
This indicates that, in addition to the cluster ions of the type HSO,(H2SO4)T X with X having a mass of 8151 amu also various other minor negative cluster ions which were detected in the stratosphere may represent fragments formed during ion sampling. A compilation of observed mass numbers for minor negative ions in ion composition measurements which may represent fragment ions is given in Table 1 along with previous tentative identifications.
Table 1:
Mass numbers
of minor
stratospheric
negative
ions which
may r2ptTSent
fragment
ions.
Mass in amu
Previous tentative identification
8022
NOjH20
9122
NOjHCl,
Possible
Ref.
fragment
so; HSO;i
HSOi 1
14321
~~~~~3H20 3 3
14422
NOjHN03H20
17822
HSO~HN03H20 HS0,HS03
17922
HS0,HN03H20 NOjHNO3HOCl
20522
NOj(HN03)2H20
(No,SO,)-HN03
24121
HSO~'(HN03) H20 HSO~HN03HS 6 3
(NO,SO,)-H2S04
27522
HSOqH2S04HN03H20
27621
HSO~H2S04HS03
37421
HSOi(H2S04)2HS03
(1) Arnold and Qiu (1984) (2) Arijs et al. (1982)
(NQjSO3)-
1
ttso;so3
.I
I
tiSO,(H2SO4)SO3
HSOq(H2S04)2S03
ion
251
Short Paper
38
32
30 0.0 1
I
I
I
t Illill
I
I I I IlId 1
0.1
ION RATIO
Figure 4:
Abundance ratios for HSOq(H2S04)n_TX and HS0i(H2S04)n cluster ions with n equal to two (275/293) and three (373/391) as observed in two balloon-borne ion composition measurements.
CONCLUSIONS The present laboratory ECA studies show that ECA of HSOjH2SO4 leads to the formation of HSOiSO3 besides HSOi. Considering this result, it is conceivable that the mixed cluster ions of the type HSO~(H*SO4)~X with X having a mass of 8151 amu which were recently observed in balloon-borne ion composition measurements in the stratosphere do not represent true ambient ions but are fragments formed by ECA of ambient HS0i(H2S04)n clusters during ion sampling into the mass probes for stratospheric HS03 or SO3.
spectrometer.
If
so,
these ions cannot
serve as
Recent in-situ ECA studies revealed that ECA of mixed HSO,(H2SO4),(HNO3), clusters involves also additional fragmentation channels resulting in fragment ions which may be misinterpreted as ambient ions in ion composition measurements.
252
ShortPaper
ACKNOWLEDGEMENTS The authors wish to express their thanks to E. Ferguson and A.A. Viggiano for stimulating discussions. Support by the technical staffs of the Max-Planck-Institut fir Kernphysik and the balloon group of the Centre National d-Etudes Spatiales at Aire-surl‘Adour, France is gratefully appreciated. This work was supported in part by the Bundesministerium fUr Forschung und Technologie through Gesellschaft fiir Strahlen- und Umweltforschung. REFERENCES Arijs,
E., Nevejans, D., Frederick, P. and Ingels, J.(1982). Stratospheric negative composition measurements, ion abundances and related trace gas detection. J.Atmos.Terr.Phys. 44, 681.
Arnold, F. and Henschen, Nature 275, 521.
G. (1978). First
mass
analysis
of stratospheric
negative
ion
ions.
Arnold, F., Viggiano, A.A. and Schlager, H.(1982). Implications for trace gases and aerosols of large negative ion clusters in the stratosphere. Nature 297, 371. Arnold, F. and Qiu, S. (1984). Upper stratosphere negative ion composition and inferred trace gas abundances. Planet. Space Sci. 32, 169.
measurements
Glebe, W. and Arnold, F. (1983). Negative acid cluster ion hydration studies of atmospheric interest. Proc.Intern. Swarm Seminar, Innsbruck, Austria 1983, 132. Holland, P.M. and Castleman, A.W. (1978). Gas phase complexes: Considerations of the stability of clusters in the sulfurtrioxide-water system. Chem.Phys.Lett. 56, 511. Knop, G. and Arnold, F. (1985). Acetone measurements in the upper troposphere stratosphere. Planet. Space Sci. (to be published).
and lower
Qiu, S. and Arnold, F. (1984). Stratospheric in situ measurements of H2SO4 and HS03 vapors during a volcanically active period. Planet. Space Sci. 32, 87. Schlager, H., Fabian, R. and Arnold, F.(1983).A new cluster ion source/ion drift cell apparatus for atmospheric ion studies - First mobility and reaction rate coefficient measurements. Proc.Intern. Swarm Seminar, Innsbruck, Austria 1983, 257. Schlager, H. and Arnold, F. (1985a). Balloon-borne of stratospheric positive ions: Unambiguous Planet.
fragment detection
ion mass
spectrometry
Space Sci. (submitted).
Schlager, H. and Arnold, F. (1985b). Acetonitrile in the stratosphere - Unambiguous identification using fragment ion mass spectrometry (to be published). Stockwell, W.R. and Calvert, J.G. (1983). The mechanism Atmos.Environ. 17, 2331.
studies
of H+(CHCN)l(H20),-clusters.
of the HO-SO2
reaction.