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Solubilities and reactions of trace gases in cold sulfuric acid aerosols
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Pergamon
J. AtrOfoi Sci.• Vol. 27. Suppl. I. pp. S6SS-S6S6. 1996 Copyright Il:i 1996 Elsev1er Science LId
PIT: 80021-8502(96)00399-0
Printedin Great Britain. All rishu re..rved 0021 ·8S02/96SIS.OO + 0.00
SOLUBILITIES AND REACTIONS OF TRACE GASES IN COLD SULFURIC ACID AEROSOLS S. LANGENBERGl, V. PROKSCH2, and U. SCHURATH2 lInstitut fiir Physikalische und Theoretische Chemie der Universitat Bonn, Wegelerstr. 12, 0-53115 Bonn 2Forschungszentrum Karlsruhe, IMK - Atrnospharische Aerosolforschung, P.O.B. 3640, 0-76021 Karlsruhe KEYWORDS Henry's law; Sulfur dioxide; Nitrogen dioxide; Gas chromatography
Heterogeneous conversionsof trace gases on/in cold sulfuric acid aerosols are of great importance in the stratosphere, and possibly in the upper troposphere, e.g. in the contrails of aircraft. Most laboratory techniques like flow reactors and Knudsen cells which have been used recently to study trace gas - sulfuric acid interactions are restricted to fast uptake due to either high solubility or very fast liquid reaction. But slower conversion rates may also be important, e.g. the formation of HONO from NOz ' Solubilities H of trace gases and their liquid phase diffusion coefficients D, are important parameters affecting conversion of trace gases on aerosol particles. We use a low temperature version of a well known gas chromatographic technique to measure H and Di: a thin sulfuric acid film (1 - 2 pm film thickness, 41 - 83 wt% sulfuric acid) is deposited as the stationary phase in a fused silica column of 530 pm i.d, and 2.8 m length. The film has to be stabilized by a surfactant. The column is immersed in a of stationary phase is determined cryo-thermostat (T = 200 - 240 K). The amount by acid base titration after use. The trace gas under investigation is injected as a sharp peak and and passed through the column by a constant carrier gas flow. The information about solution, diffusion and reaction in the liquid phase is derived from the elution profile. Due to the low film thickness, saturation of the stationary phase is possible on the timescale of our experiment. Therefore independent determinations of Hand D, are possible. This was demonstrated for S02 which is only physically absorbed in the acid [Schu95]. In order to determine Hand Di, a mixture of S02/SF6 is injected into the column. SF6 is used as an insoluble tracer. The adjusted retention time t n = tr (S0 2) - t r (SF6 ) is calculated from the peak retention times. The solubility of S02 is determined from t n and the carrier gas flow rate n.
m,
H=
nt n
(1)
m,po
Decreasing solubilities were found with increasing temperature and decreasing H2S0 4 content. S6SS
5656
Abstracts of the 1996 European Aerosol Conference 70
5 59wl%.-50·e
62wl% 4 60
-
[3 a.
50
d'2 Z
Xl 0 0
10
2
20
30
40
50
80
100
59wl%.-tiOOC
E
a. a.
:;1
-sot
0
z
X 0 0 0
10
20
30
40
lime /[5]
50
60
70
0
20
40
60
lime/[s]
Fig. 1. Comparison of peaks of S02 and N0 2 on sulfuric acid
Due to the formation of HONO, interactions of N0 2 with sulfuric acid aerosol particles may be of great importance for the atmosphere. HONO plays an important role in smog production after sunrise. Chlorine activation by HONO is recently discussed. Similar to the S02 experiments, the interaction of N0 2 was studied [Lang96]. In contrast to the S02 peaks, the retention times of the N0 2 peaks increase with increasing amounts of N0 2 injected. NO:z dimerizes at low temperature,
With increasing amounts of NO:z injected, larger amounts of N20. are formed which is more soluble in the acid. When extending the theory of chromatography to this complex system, independent determinations of solubilities of NO:z and N:zO. are possible. Using the obtained solubilities, simulation of the N0 2 peak shapes applying plate theory is possible. In this simulation equilibria of N02/N:z0. are included but no chemical reaction. In contrast to the simulated peaks, the measured peaks show tailing. This is probably caused by slow reversible conversion of N0 2 to HONO and HN03 which reacts back to NO:z after most of the N0 2 and N:zO. evaporated. REFERENCES Schurath, U., V. Proksch, S. Langenberg, (1995) Solubilities and diffusion of solutes in cold sulfuric acid films. Proceedings of the HAUPP/LACTOZ Workshop Homogeneous and heterogeneous chemical processes in the troposphere, ECC, Strasbourg, in press. Langenberg, S., V. Proksch, U. Schurath, (1996) Determination of solubilities of N0 2/N20. in sulfuric acid at low temperature. Proceedings of the EUROTRAC Symposium Transport and Transformation of Pollutants in the Troposphere, ECC-ISS, Garmisch-Partenkirchen, Germany, in preparation.
Pergamon
J. AtrOfoi Sci.• Vol. 27. Suppl. I. pp. S6SS-S6S6. 1996 Copyright Il:i 1996 Elsev1er Science LId
PIT: 80021-8502(96)00399-0
Printedin Great Britain. All rishu re..rved 0021 ·8S02/96SIS.OO + 0.00
SOLUBILITIES AND REACTIONS OF TRACE GASES IN COLD SULFURIC ACID AEROSOLS S. LANGENBERGl, V. PROKSCH2, and U. SCHURATH2 lInstitut fiir Physikalische und Theoretische Chemie der Universitat Bonn, Wegelerstr. 12, 0-53115 Bonn 2Forschungszentrum Karlsruhe, IMK - Atrnospharische Aerosolforschung, P.O.B. 3640, 0-76021 Karlsruhe KEYWORDS Henry's law; Sulfur dioxide; Nitrogen dioxide; Gas chromatography
Heterogeneous conversionsof trace gases on/in cold sulfuric acid aerosols are of great importance in the stratosphere, and possibly in the upper troposphere, e.g. in the contrails of aircraft. Most laboratory techniques like flow reactors and Knudsen cells which have been used recently to study trace gas - sulfuric acid interactions are restricted to fast uptake due to either high solubility or very fast liquid reaction. But slower conversion rates may also be important, e.g. the formation of HONO from NOz ' Solubilities H of trace gases and their liquid phase diffusion coefficients D, are important parameters affecting conversion of trace gases on aerosol particles. We use a low temperature version of a well known gas chromatographic technique to measure H and Di: a thin sulfuric acid film (1 - 2 pm film thickness, 41 - 83 wt% sulfuric acid) is deposited as the stationary phase in a fused silica column of 530 pm i.d, and 2.8 m length. The film has to be stabilized by a surfactant. The column is immersed in a of stationary phase is determined cryo-thermostat (T = 200 - 240 K). The amount by acid base titration after use. The trace gas under investigation is injected as a sharp peak and and passed through the column by a constant carrier gas flow. The information about solution, diffusion and reaction in the liquid phase is derived from the elution profile. Due to the low film thickness, saturation of the stationary phase is possible on the timescale of our experiment. Therefore independent determinations of Hand D, are possible. This was demonstrated for S02 which is only physically absorbed in the acid [Schu95]. In order to determine Hand Di, a mixture of S02/SF6 is injected into the column. SF6 is used as an insoluble tracer. The adjusted retention time t n = tr (S0 2) - t r (SF6 ) is calculated from the peak retention times. The solubility of S02 is determined from t n and the carrier gas flow rate n.
m,
H=
nt n
(1)
m,po
Decreasing solubilities were found with increasing temperature and decreasing H2S0 4 content. S6SS
5656
Abstracts of the 1996 European Aerosol Conference 70
5 59wl%.-50·e
62wl% 4 60
-
[3 a.
50
d'2 Z
Xl 0 0
10
2
20
30
40
50
80
100
59wl%.-tiOOC
E
a. a.
:;1
-sot
0
z
X 0 0 0
10
20
30
40
lime /[5]
50
60
70
0
20
40
60
lime/[s]
Fig. 1. Comparison of peaks of S02 and N0 2 on sulfuric acid
Due to the formation of HONO, interactions of N0 2 with sulfuric acid aerosol particles may be of great importance for the atmosphere. HONO plays an important role in smog production after sunrise. Chlorine activation by HONO is recently discussed. Similar to the S02 experiments, the interaction of N0 2 was studied [Lang96]. In contrast to the S02 peaks, the retention times of the N0 2 peaks increase with increasing amounts of N0 2 injected. NO:z dimerizes at low temperature,
With increasing amounts of NO:z injected, larger amounts of N20. are formed which is more soluble in the acid. When extending the theory of chromatography to this complex system, independent determinations of solubilities of NO:z and N:zO. are possible. Using the obtained solubilities, simulation of the N0 2 peak shapes applying plate theory is possible. In this simulation equilibria of N02/N:z0. are included but no chemical reaction. In contrast to the simulated peaks, the measured peaks show tailing. This is probably caused by slow reversible conversion of N0 2 to HONO and HN03 which reacts back to NO:z after most of the N0 2 and N:zO. evaporated. REFERENCES Schurath, U., V. Proksch, S. Langenberg, (1995) Solubilities and diffusion of solutes in cold sulfuric acid films. Proceedings of the HAUPP/LACTOZ Workshop Homogeneous and heterogeneous chemical processes in the troposphere, ECC, Strasbourg, in press. Langenberg, S., V. Proksch, U. Schurath, (1996) Determination of solubilities of N0 2/N20. in sulfuric acid at low temperature. Proceedings of the EUROTRAC Symposium Transport and Transformation of Pollutants in the Troposphere, ECC-ISS, Garmisch-Partenkirchen, Germany, in preparation.