F. Arnold

Ion-induced nucleation of atmospheric water vapor at the mesopause

Abstract The possibility of aerosol formation at the mesopause by ion-induced water vapor nucleation is investigated. A simple kinetic model considering new information on ion-growth and -recombination processes as well as on mesospheric water vapor and temperatures is put forward. It predicts ion-nucleation to be possible only at high latitudes during local summer in a narrow height region, extending from about 88 to 91 km. Derived nucleation rates increase steeply with decreasing temperatures and electron number densities. If for the latter typical values are considered nucleation rates may become sufficiently high to account for the observed mesospheric aerosol layer. Various observed characteristic temporal and spatial variations of the aerosol layer including its response to geomagnetic activity may be explained by the model.

Balloon-borne composition measurements of stratospheric negative ions and inferred sulfuric acid vapor abundances during the MAP/GLOBUS 1983 campaign☆

Abstract Balloon-borne composition measurements of stratospheric negative ions were carried out at altitudes between about 30 and 40 km using two improved mass spectrometer probes with high sensitivity and mass resolution mounted on a gondola carried by a 350,000 m3 balloon. In order to minimize the risk of contamination, data were taken only at float altitude and during balloon descent. Besides the major ion species, HSO4- (H2SO4)l(HNO3)m and NO3- (HNO3)n, various minor ion species were detected including also mixed clusters with H2O, SO3 and possibly HOCl ligands. It appears that the SO3 ligands were formed by electric field-induced collisional cluster ion fragmentation during sampling of the ions into the mass spectrometer. Sulfuric acid vapor abundances inferred from the present negative ion composition data reveal the presence of a sulfuric acid vapor layer with a pronounced maximum around 37 km with a H2SO4 vapor concentration of about 3 × 106 cm−3, which is in accord with a previous measurement by our group. The occurrence of a maximum suggests that sulfuric acid vapor is efficiently removed at heights above about 37 km. Potential removal processes include photolysis, OH-attack and eventually also reactions with meteor smoke particles.

Stratospheric trace gas analysis from ions: H2O and HNO3

A new method for stratospheric trace gas analysis based upon in situ ion composition measurements is presented. The strength of the method lies in its extremely high sensitivity which at present allows for detection limits of the order of 100–1000 molecules cm−3 corresponding to volume mixing ratios of the order of 10−15–10−14 around 35 km altitude. The typical uncertainty of derived trace gas abundances is plus or minus a factor of about two. A disadvantage lies in the selectivity of the method which is restricted to trace gases having either large proton affinities, dipole moments or gas phase acidities. Analyses of water vapor and nitric acid vapor in the upper stratosphere are presented.

Combined mass spectrometric composition measurements of positive and negative ions in the lower ionosphere—I. Positive ions

Abstract Negative ion composition measurements of the lower ionosphere made simultaneously with positive ion measurements show some interesting features not previously observed. The higher sensitivity of this instrument allowed for detection of numerous previously undetected species. A layer of heavy ions (> 100 a.m.u.) was observed to exist between 80 and 90 km. The properties of this layer seem to indicate a meteoric source. The heavy ions are seen to exist down to the lowermost heights measured and their abundance increases below 58 km indicating a stratospheric source. Besides these ions, numerous new light ions were also seen. Their abundance level and sources are discussed.

Upper stratosphere negative ion composition measurements and inferred trace gas abundances

Abstract In situ composition measurements of atmospheric negative ions were made at 40.8 km altitude using a balloon-borne mass spectrometer with large mass range and improved mass resolution. The data obtained show marked differences compared to previous data obtained mostly around or below 33 km. It appears that these differences are mostly due to a higher atmospheric temperature, a lower nitric acid vapour abundance and a larger HSO3-vapour abundance prevailing at the higher altitude. A particularly striking feature is the relatively large fractional abundance of HSO3-containing cluster ions. Another interesting result is that nitric acid vapour abundances can be inferred from the negative ion composition data with better accuracy than is possible for lower altitudes. The reason being that collisional ion dissociation occurring during ion sampling is less disturbing. The inferred nitric acid vapour abundance for 40.8 km altitude is consistent with current 2-dimensional model calculations.

First composition measurements of positive ions in the upper troposphere

Abstract First mass-spectrometric composition measurements of atmospheric ions between 3250 and 11700 m altitude are reported. They reveal the presence of very massive cluster ions, the majority of which cannot be attributed to a single hydrated ion family like, for example H+(H2O)n. The observed fraction of very massive ions increases with decreasing altitude. Masses as large as about 540 amu were observed at 8200 m altitude. Implications of the observations for ion and nucleation processes are discussed.

Stratospheric negative ions—detailed height profiles

Balloon-borne mass spectrometers with extended mass range have been flown during controlled descents. This gave detailed height profiles of stratospheric negative ions between 15 and 34 km. The main ion families were HSO4−(H2SO4)m(HNO3)n and NO3− (HNO3)n Information concerning trace gases is o well as an assessment of the problems of ion fragmentation and contamination. Finally, the data are used to derive information concerning the rate of H2SO4 clustering.

Silicon negative ion chemistry in the atmosphere-in situ and laboratory measurements

Abstract The results of a rocket-borne mass spectrometer measurement indicate that large concentrations of negative ions exist above the bottom of the atmospheric atomic oxygen layer. A large majority of these ions have a mass greater than 100 amu. In addition, an ion at mass 76 was observed with concentrations too large to be CO4−. In order to explain these features, a number of reactions involving silicon oxide negative ions have been measured in a flowing afterglow system. The ion SiO3− is produced by reaction of O3−, and CO3−, with SiO. The SiO3− ion is extremely stable and does not react measurably with NO, NO2, CO, CO2, O3 or O. Since meteoroid ablation produces a large silicon input into the atmosphere, it appears possible that the ions observed at mass 76 may be SiO3−. Possible production mechanisms for this ion as well as the heavy ions are discussed.

Stratospheric in situ measurements of H2SO4 and HSO3 vapors during a volcanically active period

In situ measurements of stratospheric H2SO4 and HSO3vapors using passive chemical ionization mass spectrometry were made in October 1982 after the eruption of volcano El Chichon. Data were obtained between about 20 and 41 km showing [H2SO4 + HSO3] sum concentrations between about 104 and 2 × 105 cm−3 below 29 km and a steep rise above this altitude. Maximum [H2SO4 + HSO3] values of about 3 × 106 cm−3 are reached above 35 km. Partial [HSO3] concentrations increase above 34 km reaching about 4 × 105cm−3 around 40 km. From the measurements it is concluded that H2SO4 and probably HSO3photolysis have an important influence above 34 km leading to the observed increase of [HSO3] and a depletion of H2SO4vapor. It also seems that the data support the view of heterogeneous HSO3 removal. If correct, this would imply that stratospheric aerosols are formed primarily from HSO3 rather than H2SO4vapor.

Atmospheric acetonitrile measurements in the tropopause region using aircraft-borne active chemical ionization mass spectrometry

Abstract Additional lower stratospheric acetonitrile measurements were carried out using aircraft-borne ACIMS (Active Chemical Ionization Mass Spectrometry). Volume mixing ratios were found to range between 8.5 and 30 pptv (parts per trillion by volume) with an average of 23 pptv. When compared to our first ACIMS measurements and recent ground-level measurements, the present data turn out quite similar, which suggest that acetonitrile is well mixed within the troposphere. By contrast, the present data are about 10–20 times higher than middle stratospheric acetonitrile abundances inferred from balloonborne ambient ion composition measurements.