C. Piesch

Retrieval of stratospheric O3, HNO3 and ClONO2 profiles from 1992 MIPAS-B limb emission spectra: Method, results, and error analysis

Within the framework of the European Arctic Stratospheric Ozone Experiment, two flights of the balloon-borne MIPAS-B limb emission spectrometer were performed in the Arctic stratosphere from Kiruna, northern Sweden. During the early hours of January 13 and the night from March 14 to March 15, 1992, several limb sequences of infrared spectra were recorded which have permitted the retrieval of vertical profiles of many trace gases relevant for ozone chemistry. In the present work, the retrieval strategy, error estimation strategy, and resulting profiles of O3, HNO3, and ClONO2 are reported. The data analysis procedure, consisting of data preprocessing including calibration, analysis of auxiliary data including temperature profiles and line of sight determination, and retrieval of trace gas profiles, is described in detail. The last is carried out by means of multiparameter nonlinear least squares fitting in combination with onion peeling. An astonishingly high ClONO2 amount of 2.6 ppb by volume at about 19-km altitude was inferred for the March flight. A rigorous error analysis, which takes into account systematic and random errors and their often nonlinear impact on the results, proves the significance of the retrieved trace gas profiles.

The variability of ClONO2 and HNO3 in the Arctic polar vortex : comparison of Transall Michelson interferometer for passive atmospheric sounding measurements and three-dimensional model results

A three-dimensional radiative-dynamical-chemical model has been used to investigate measurements of column ClONO2 and HNO3 made by the airborne Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instrument. MIPAS made measurements from the Transall aircraft in the northern hemisphere lower stratosphere from December 1992 to March 1993. The three-dimensional model has a detailed stratospheric chemistry scheme including heterogeneous reactions on polar stratospheric clouds and sulfate aerosols. The circulation in the model is specified from the European Centre for Medium Range Weather Forecasts analyses. The MIPAS measurements reveal large variability in column ClONO2 at the edge of the polar vortex. For the measurements of January 27 and 31, 1993, the model experiments show that variability in ClONO2 observed over this period can be explained by polar stratospheric cloud processing and recovery. Measurements of ClONO2 on February 2, 1993, showed large variations depending on the orientation of the aircraft relative to the edge of the vortex. Results from the model show that this is qualitatively consistent with the aircraft flying near to the collar region with its associated strong horizontal gradients of ClONO2. The models ability to simulate these strong gradients is limited by its relatively coarse resolution. In early March the vortex became very distorted. During this period MIPAS measured very large values of ClONO2 at high latitudes within the vortex but lower, although still large, values in the more southerly regions of the vortex. At this stage of the winter ClONO2 is the major chlorine species in the model at high latitudes. The model shows how the distortion of the vortex in March led to relatively high columns of ClONO2 in vortex air over southern Europe. The model also reproduces the observed gradient in ClONO2 within the vortex, and experiments show that these gradients are due, at least in part, to the availability of sunlight. This variability of ClONO2, and therefore active chlorine (ClOχ), implies that these tracers do not correlate well with potential vorticity. This places limitations on extrapolating localized measurements of anything but the longest lived chemical tracers to the whole of the polar vortex using potential vorticity, or indeed a long-lived tracer, as part of a coordinate system.

Determination of the stratospheric organic chlorine budget in the spring arctic vortex from MIPAS B limb emission spectra and air sampling experiments

Vertical profiles of halogenated source gases, CF 2 Cl 2 , CFCl 3 , CHF 2 Cl, Cl 4 , and CF 4 , were retrieved from limb emission spectra recorded by the Michelson Interferometer for Passive Atmospheric Sounding, Balloonborne version (MIPAS B) during a balloon flight launched from Esrange near Kiruna, northern Sweden (68°N) on March 14, 1992. This flight was a contribution to the balloon launch program of the European Arctic Stratospheric Ozone Experiment (EASOE) campaign. All problems encountered during the analysis of the recorded spectra are discussed in detail. These are primarily the lack of spectral data for HNO 3 which interferes with the CF 2 Cl 2 ν 6 band, and the strong effects attributed to the Pinatubo aerosol. As the air mass sounded by MIPAS was polar vortex air, these data supplement the results of in situ air sampling experiments, which investigated air masses outside or at the edge of the polar vortex at altitudes below 18 km during the last phase of EASOE. An analysis is made of the vertical profiles of the seven most abundant organic chlorine species (CF 2 Cl 2 , CFCl 3 , CHF 2 Cl, CCl 4 , CH 3 Cl, CH 3 CCl 3 , and C 2 F 3 Cl 3 ) during that phase of the EASOE campaign. Mixing ratios of those organic chlorine compounds which had not been measured by MIPAS are inferred from profiles provided by air sampling experiments performed between November 30, 1991, and March 12, 1992. These profiles were adjusted to the dynamic conditions during the MIPAS observations, namely the effect of subsidence, using CF 2 Cl 2 as a tracer. This allowed to derive the relative contributions of the organic chlorine species to the total chlorine budget of the air mass sounded by MIPAS. The results are consistent with the high ClONO 2 mixing ratio of 2.6 parts per billion by volume (ppbv) observed at 18.9-km altitude during this flight of MIPAS B.

Spatial and temporal variability of ClONO2, HNO3, and O3 in the Arctic winter of 1992/1993 as obtained by airborne infrared emission spectroscopy

In the winter of 1992/1993 the airborne Michelson interferometer for passive atmospheric sounding (MIPAS-FT) was operated on board a German research aircraft (Transall C-160) to record infrared emission spectra of the atmosphere inside and outside the Arctic vortex. Measurements were made during four campaigns between December 4, 1992, and March 29, 1993, in the European Arctic as well as over central and southern Europe (82°N–37.5°N). We present the retrieved zenith column amounts of the stratospheric trace gases ClONO2, HNO3, and O3 of this period. Inside the polar vortex, the column amounts of ClONO2 and HNO3 were considerably enhanced already in early December, up to 3.1×1015 cm−2 and 2.7×1016 cm−2, respectively. Around the end of January, low ClONO2 (1×1015 cm−2) and high HNO3 column amounts (up to 3.7×1016 cm−2) were observed inside the vortex, whereas a highly variable “collar” of ClONO2 had developed at the vortex edge. During March, after temperatures had been above the threshold for polar stratospheric clouds (PSCs) for several weeks, we measured lower HNO3 (below 2.5×1016 cm−2) and very high ClONO2 column amounts (up to 6×1015 cm−2) inside the vortex. Thus a major part of the reactive chlorine had been converted into ClONO2, and the potential for rapid ozone depletion was reduced markedly in the region observed. On March 10, when the polar vortex extended southward to the Mediterranean, ClONO2 column amounts as high as 4.6×1015 cm−2 were observed at 40°N. At the end of March, considerable amounts of ClONO2 (up to 3.4×1015 cm−2) were measured also far outside the vortex.

Airborne remote sensing of NO2 in the Arctic winter of 1994–1995 and comparison with a three‐dimensional chemical transport model

In the winter of 1994–1995, for the first time NO2 was observed by the Michelson Interferometer for Passive Atmospheric Sounding-Flugzeug Transall (MIPAS-FT). We present the NO2 data of MIPAS and of a Differential Optical Absorption Spectroscopy (DOAS) instrument, which was also operated on the Transall, and compare the measurements with the Single Layer Isentropic Model for Chemistry And Transport (SLIMCAT). The daytime midlatitude NO2 column amounts of MIPAS and DOAS increased from 1×1015 cm−2 in December to ∼3×1015 cm−2 in March. After sunset MIPAS observed strong NO2 increases, up to 3.2×1015 cm−2 on December 20, up to 7.2×1015 cm−2 on January 17 and up to 6.4×1015 cm−2 on March 27. These high nighttime values, showing considerable amounts of NOx in the midlatitude stratosphere, were qualitatively reproduced by SLIMCAT. The NO2 columns measured inside the Arctic vortex, ≤1×1015 cm−2 from December until mid-January with no substantial increase after sunset, displayed strong denoxification. From the end of January the Arctic daytime NO2 columns grew to ∼2×1015 cm−2, and after sunset MIPAS observed similar strong increases as at midlatitudes, up to 3.4×1015 cm−2 on January 24 and up to 4.8×1015 cm−2 in March and April. The renoxification of the vortex was also shown by SLIMCAT. On April 5, MIPAS NO2 column amounts decreased by 1.5×1015 cm−2 after reaching the maximum, caused by N2O5 and ClONO2 formation and encounter of less renoxified air masses.

High-speed cinematographic recording and numerical simulation of particles depositing on electret fibres

Abstract A method is described for visualization and recording, as well as for numerical simulation of particle motion during the deposition onto single electrically charged filter fibres (electret fibres). For this a microscope and a high-speed cine camera are used to record the trajectories of particles in the process of flowing around, and being deposited on, a fibre (two-dimensionally in a plane perpendicular to the fibre axis). The particle trajectories are then modeled, based on the experimental data and suitable mathematical models for the fluid flow and the electric fields of the fibre charges. As the fibre charge density, in general, is not known, it is used as a fitting parameter in the model calculation. Using the example of split-fibres with a rectangular cross-section and a bipolar electric charge it is shown that, using models known from the literature, very good agreement can be achieved between experiment and simulation. With this electret fibre type, the trajectory simulations, assuming an ideal bipolar charge configuration, gave effective charge densities between roughly 100 and 500 μAs m−2, corresponding to total surface charge densities between 230 and 1150 μAs m−2.