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Mixing ratios of the conserved tracers SF6 and CO2 in air samples collected with cryogenic whole-air samplers during two balloon flights in the Arctic and mid-latitude stratosphere up to 30 km altitude in 1997 are presented. The data are used to derive the mean age of stratospheric air. The calculated CO2-ages agree with the corresponding SF6-ages to within 0.5 years. These results do not confirm the findings previously reported by Harnisch et al. [1998] but rather suggest that SF6 and CO2 can be regarded as equivalent age tracers. However, evidence is presented that this general agreement may not be valid for polar stratospheric air parcels that comprise fractions of mesospheric air.

Under the extremely cold conditions in the polar winter stratosphere, heterogeneous reactions involving HCl and CIONO(sub 2) on the surfaces of polar stratospheric cloud particles can release large amounts of reactive chlorine from these reservoirs leading to rapid chemical loss of ozone in the Arctic lower stratosphere during late winter and early spring.

Simultaneous balloon-borne in situ measurements of total reactive nitrogen (NO ) and nitrous oxide (N 2 O) were made up to 29 km over Kiruna, Sweden (68°N, 21°E) on February 10 and 25, 1997. Kiruna was located at the edge or inside of the Arctic vortex at potential temperatures between 475 (∼19 km) and 675 K (∼26 km). Below 500 K (∼21 km) the N 2 O values were >120 ppbv on both days, and the observed NO mixing ratios agreed well with those calculated using the NO y -N 2 O correlation previously obtained at northern midlatitudes. An exception was a sharp dip in NO at 445 K (18.4 km) observed on February 25. Back trajectory analyses indicate that this layer had experienced cold temperatures close to ice saturation, i.e., favorable conditions for denitrification. Between 500 and 600 K (∼24 km) the N 2 O values were

The long term temporal trend of CCl2F2 (CFC-12) in the lower stratosphere has been derived from a series of balloon-borne observations of long-lived trace gases made since 1978. In order to remove the effect of dynamical processes in the individual profile observations, nitrous oxide (N2O) is used as a vertical coordinate. The calculated trend in the lowermost stratosphere follows the observed tropospheric increase very closely, however, the observed mixing ratios in the lowermost stratosphere appear to lag the global mean tropospheric trend by about one year. The most recent observations indicate that the slowing down of the tropospheric increase has propagated into the lowermost stratosphere. While CFC-12 increased at an average rate of 18.5±1.8 ppt per year between 1978 and 1990, the growth rate decreased to 11.9±4.2 ppt per year between 1990 and 1997.

Total reactive nitrogen (NO(y)), nitrous oxide (NO2), methane (CH4), and ozone (03) were measured on board a balloon launched from Aire sur l'Adour (44 deg N, 0 deg W), France on October 12, 1994. Generally, NO(y) was highly anti-correlated with N2O and CH4 at altitudes between 15 and 32 km. The linear NO(y) - N2O and NO(y) - CH4 relationships obtained by the present observations are very similar to those obtained on board ER-2 and DC-8 aircraft previously at altitude below 20 km in the northern hemisphere. They also agree well with the data obtained by the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument at 41 deg N in November 1994. Slight departures from linear correlations occurred around 29 km, where N2O and CH4 mixing ratios were larger than typical midlatitude values, suggesting horizontal transport of tropical airmasses to northern midlatitudes in a confined altitude region.

Vertical profiles of H2O and CH4 were measured using in situ techniques in the Arctic winter stratosphere during the European Arctic Stratospheric Ozone Experiment (EASOE) 1991/1992 in the pressure range between 12 and 80 hPa. The measurements were grouped according to the meteorological situation, i.e., their position relative to the polar vortex. The mixing ratio of the quantity 2·CH4 + H2O was determined in the altitude region between the hygropause and 30 km to be quasi constant at a mean mixing ratio of 6.91 ± 0.41 ppmv. No significant difference of 2·CH4 + H2O was observed inside and outside the vortex. From the correlation between CH4 and H2O ΔH2O/ΔCH4, i.e., the water vapor yield of the methane oxidation, was calculated to be −1.82 ± 0.21. The globally averaged H2O mixing ratio of air entering the stratosphere was found to be 3.61 ± 0.28 ppmv. The data are compared with studies on the total hydrogen budget over the past 20 years. Despite the variety of instrumental techniques used in these studies, an increase of total hydrogen is apparent over this period.

Global distributions of CH4 in the mesosphere and stratosphere have been measured continuously since October 11, 1991, by the Halogen Occultation Experiment (HALOE) onboard the UARS. CH4 mixing ratio is obtained using the gas filter correlation technique operating in the 3.3-μm region. Since measurements are made during solar occultation in the 57° inclination orbit, data are collected 15 times daily for both sunrises and sunsets. This provides coverage of one hemisphere in a month period. One complete hemispheric sweep (from equator to ∼80° latitude) is made during the spring and summer seasons of two hemispheres, and a partial sweep (from equator to around 50° latitude) is made during the fall and winter seasons of two hemispheres. HALOE CH4 measurements are validated using direct comparisons with correlative data and internal consistency checks using other HALOE-measured tracers, HF, and aerosols. It is estimated for the 0.3- to 50-mbar region that the total error, including systematic and random components, is less than 15% and that the precision is better than 7%. The CH4 gas filter channel does not depend significantly on the Pinatubo aerosol extinction. An experimentally accurate measurement of CH4 is very important because CH4 is a primary interfering gas in the HALOE HCl channel and, subsequently, can cause HCl measurement error. Simultaneous measurements of CH4 and other HALOE species (O3, H2O, NO, NO2, HCl, HF, and aerosol extinction coefficients) provide important information on atmospheric dynamic and chemical processes, since CH4 can be used as a tracer and an indicator of atmospheric transport processes. Several new pieces of information on previously unreported HALOE-observed features are also presented.

We present an analysis of chlorine chemistry in the Arctic stratosphere during the winter of 1991/92 and assess its potential implications for ozone depletion. In accordance with observations of total organic chlorine, ClONO2 and HCl, box model results indicate the following: (1) An almost complete activation of chlorine during the cold winter period. (2) A possible contribution from the heterogeneous reaction HOCl + HCl and the gas-phase reaction CH3O2 + ClO to the complete conversion of HCl to active chlorine. (3) A strong buildup of ClONO2 following PSC disappearance which remains the main chlorine reservoir for about a month, after which HCl becomes dominant. (4) Appreciable chemical ozone loss in the lower stratosphere inside the polar vortex is conceivable for the winter of 1991/92.

[1] Vertical profiles of nitrous oxide and methane at high latitudes (57–72°N; 64–89°S) were observed by the Improved Limb Atmospheric Spectrometer (ILAS) solar occultation sensor aboard Advanced Earth Observing Satellite. These measurements were made continuously from November 1996 through June 1997 with some additional periods in September–October 1996. A validation study of the nitrous oxide and methane data processed with the Version 5.20 ILAS retrieval algorithm is presented in this paper. Comparisons are made with (1) nitrous oxide and methane obtained by the ILAS validation balloon campaigns at Kiruna, Sweden, and at Fairbanks, Alaska, in the Arctic; (2) nitrous oxide and methane by the Photochemistry of Ozone Loss in the Arctic Region in Summer aircraft campaign in the Arctic; (3) nitrous oxide by the ground-based spectroscopic measurements and by the aircraft-based remote sensing measurements in the Arctic; and (4) methane by satellite measurements of the Version 19 Halogen Occultation Experiment in the Arctic and Antarctic. Comparisons of ILAS nitrous oxide and methane with Upper Atmosphere Research Satellite Reference Atmosphere data are also made. The results of the comparisons and additional ILAS internal consistency analyses are as follows: (1) the uncertainty of ILAS nitrous oxide is better than 10% over 10–30 km in altitude, and is larger than 50% over 30–40 km, which is comparable to the expected total errors of the ILAS measurements; (2) the uncertainty of ILAS methane is better than 10% over 10–50 km, except for 15–30 km in winter with positive biases exceeding 20%, which is smaller than or comparable to the expected total errors of the ILAS measurements (the quality of ILAS methane in the polar lower stratosphere is better in summer than in winter). In summary, the characteristics of ILAS measurements, i.e., high sampling frequency in polar latitudes with high vertical resolution, along with the good quality of ILAS Version 5.20 nitrous oxide for 10–40 km and the good quality of ILAS Version 5.20 methane for 10–50 km except for 15–30 km in winter, make the ILAS nitrous oxide and methane data set valuable for scientific study of various polar stratospheric phenomena.

A prerequisite to studying phenomena in the winter stratospheric polar vortex is the separation of measurements inside and outside the dynamical barrier of the vortex edge. We describe a technique to accurately determine the inner edge of the vortex boundary region from measurements of potential temperature and a trace gas, such as N2O, and apply it to in situ aircraft and balloon measurements from the SOLVE/THESEO 2000 Arctic campaign. The method may be used to refine the Nash algorithm, which, due to the inherently coarser resolution of potential vorticity on which it is dependent, may misidentify the inner edge by more than 400 km and omit the identification of small, extravortex filaments within the vortex.

[1] We present balloon-borne observations of CO2 and SF6 and derived vertical profiles of mean age for polar winter (inside vortex) and for midlatitude (nonwinter) conditions. For SF6-derived mean ages above 5 years a mesospheric SF6 sink may lead to an overestimation of mean age, while for younger mean ages (below 2 years) the seasonal cycle of CO2 may influence the mean age determination based on CO2. We suggest that SF6 be used as an age tracer in the lower part of the stratosphere (i.e., for low mean age), whereas CO2 will be the better age tracer for older air. The mean age distributions together with an estimate of the width of the age spectrum are used to estimate the stratospheric chlorine loading. On the basis of an emission scenario and the lifetimes of chlorine-containing compounds we estimate the future stratospheric chlorine loading. Inside the polar vortex, at an altitude of 20 km, we expect total chlorine to return to the values present in this region in 1980, when the ozone hole first appeared, around the year 2060. This estimate is based on the assumption that the general transport characteristics will not change over the period of the analysis and can thus be regarded as a best estimate based on stationary transport, the assumed set of lifetimes and emissions, and the mean age distribution derived from our measurements. As other factors influencing ozone may undergo temporal changes, this does not mean that ozone will necessarily recover at this time. While total chlorine is probably a good proxy for inorganic chlorine at altitudes above 20 km inside the polar vortex, the changing halocarbon mix may actually lead to an earlier return of inorganic chlorine to pre-ozone-hole values at lower altitudes.

[1] Carbonyl sulfide (COS) was measured in surface seawater during two Atlantic cruises. The daily mean concentration of COS is correlated to the daily means of global radiation, CH3SH concentration, hydrolysis lifetime of COS in seawater, and the logarithm of chlorophyll a concentration. An empirical model for the COS concentration has been developed on the basis of correlations between the COS concentration and these parameters. The model appears to be a promising tool for estimating COS concentrations in surface seawater from satellite observations.

[1] We employ Halogen Occultation Experiment (HALOE) observations and balloon-borne measurements (on the large Observations of the Middle Stratosphere [OMS] and Triple balloons, as well as on two small balloons) to investigate ozone loss in the stratospheric vortex in the 1999–2000 Arctic winter. Using HF and CH4 as long-lived tracers, we identify chlorine activation and chemical ozone destruction in the polar vortex. Reference relations, representative of chemically undisturbed “early vortex” conditions, are derived from the OMS remote and in situ balloon measurements on 19 November and 3 December 1999, respectively. Deviations from this “early vortex” reference are interpreted as chemical ozone loss and heterogeneous chlorine activation. The observations show an extensive activation of chlorine; in late February 2000, the activation extends to altitudes of 600 K. Between 360 and 450 K chlorine was almost completely activated. At that time, about 70% of the HCl column between 380 and 550 K was converted to active chlorine. Furthermore, the measurements indicate severe chemical ozone loss, with a maximum loss of over 60% in the lower stratosphere (415–465 K) by mid-March 2000. Substantial ozone loss was still observable in vortex remnants in late April 2000 (80 ± 10 Dobson units [DU] between 380 and 550 K). The average loss in column ozone between 380 and 550 K, inside the vortex core, in mid-March amounted to 84 ± 13 DU.

Ozone mixing ratios in the vicinity of the 525-K potential temperature surface in January and early February of 1990 were observed to decrease sharply across the edge of the vortex boundary, where the vortex position was estimated from Ertel's potential vorticity. The changes in NO(y) mixing ratio with respect to altitude measured on January 18 and 31 were quite well correlated with those of ozone between 15 and 24 km, indicating that NO(y) also had a large gradient across the edge of the vortex. This is interpreted as being mainly due to the significant denitrification that occurred inside the vortex. The total amount of gas and particulate phase HNO3 was close to the NO(y) amount at the altitude of the 22- to 23-km region, suggesting that the conversion of non-HNO3 reactive nitrogen to HNO3 had occurred with a PSC.

The mixing ratio of formaldehyde (HCHO) has been determined for air samples collected at a moderately polluted continental site (Julich, Federal Republic of Germany) and for samples collected at coastal sites in Ireland and New Zealand. In addition the HCHO mixing ratio has been determined for air samples collected in the North and South Atlantic during a cruise of the F/S Meteor from Hamburg at 55°N to Montevideo at 35°S in October and November 1980. The HCHO mixing ratio in clean tropical marine air is of the order of 0.2 parts per billion by volume, about 50% lower than predicted by current photochemical models that include CH4 oxidation as the only source for HCHO. In the mid-Atlantic, diurnal variations of the HCHO mixing ratio showing weak maxima during the early afternoon were occasionally observed. These variations may be attributed to the diurnal behavior of the photochemical and physical processes which determine the mixing ratio of HCHO during stable weather conditions. The results are discussed with regard to the currently accepted theory of the photochemistry of HCHO in the clean troposphere. It appears that the yield of HCHO formation through hydrocarbon photooxidation in the background marine troposphere is less than assumed from model considerations, most probably because of the lack of sufficiently high NO concentrations.