Altitude profile and sunset decay measurements of stratospheric nitric oxide

In July 1974 an NO/O₃ chemiluminescent instrument was used to obtain measurements of NO in the stratosphere during two balloon flights launched from Churchill (59°N, 95°W). On the first flight, an altitude profile was obtained in which the NO volume mixing ratio was observed to increase from 0.3 to 2.7 ppbv between 19 and 29.5 km. On the second flight, the mixing ratio was observed to increase from 0.25 to 2.7 ppbv between 19 and 29 km and to remain almost constant at about 2.7 ppbv from 29 to 34.5 km. On this flight, the sunset decay of NO was also obtained while the payload was at a constant float altitude of 34.5 km. These decay measurements are compared satisfactorily with the results obtained from a time dependent stratospheric model.     

The 1985 chlorine and fluorine inventories in the stratosphere based on ATMOS observations at 30° north latitude

The set of high-resolution infrared solar observations made with the Atmospheric Trace Molecule Spectroscopy (ATMOS)-Fourier transform spectrometer from onboard Spacelab 3 (30 April-1 May 1985) has been used to evaluate the total budgets of the odd chlorine and fluorine chemical families in the stratosphere. These budgets are based on volume mixing ratio profiles measured for HCl, HF, CH₃Cl, ClONO₂, CCl₄, CCl₂F₂, CCl₃F, CHClF₂, CF₄, COF₂, and SF₆ near 30° north latitude. When including realistic concentrations for species not measured by ATMOS, i.e., the source gases CH₃CCl₃ and C₂F₃Cl₃ below 25 km, and the reservoirs ClO, HOCl and COFCl between 15 and 40 km (five gases actually measured by other techniques), the 30° N zonal 1985 mean total mixing ratio of chlorine, Cl, was found to be equal to (2.58±0.10) ppbv (parts per billion by volume) throughout the stratosphere, with no significant decrease near the stratopause. The results for total fluorine indicate a slight, but steady, decrease of its volume mixing ratio with increasing altitude, around a mean stratospheric value of (1.15±0.12) ppbv. Both uncertainties correspond to one standard deviation. These mean springtime 1985 stratospheric budgets are commensurate with values reported for the tropospheric Cl and F concentrations in the early 1980s, when allowance is made for the growth rates of their source gases at the ground and the time required for tropospheric air to be transported into the stratosphere. The results are discussed with emphasis on conservation of fluorine and chlorine and the partitioning among source, sink, and reservoir gases throughout the stratosphere.     

Regional Sources of Methyl Chloride, Chloroform and Dichloromethane Identified from AGAGE Observations at Cape Grim, Tasmania, 1998–2000

There are large uncertainties in identifying and quantifying the natural and anthropogenic sources of chloromethanes – methyl chloride (CH₃Cl), chloroform (CHCl₃) and dichloromethane (CH₂Cl₂), which are responsible for about 15% of the total chlorine in the stratosphere. We report two years of in situ observations of these species from the AGAGE (Advanced Global Atmospheric Gas Experiment) program at Cape Grim, Tasmania (41° S, 145° E). The average background levels of CH₃Cl, CHCl₃ and CH₂Cl₂ during 1998–2000 were 551± 8, 6.3± 0.2 and 8.9± 0.2 ppt (dry air mole fractions expressed in parts per 10¹²) respectively, with a two-year average amplitude of the seasonal cycles in background air of 25, 1.1 and 1.5 ppt respectively. The CH₃Cl and CHCl₃ records at Cape Grim show clear episodes of elevated mixing ratios up to 1300 ppt and 55 ppt respectively, which are highly correlated, suggesting common source(s). Trajectory analyses show that the sources of CH₃Cl and CHCl₃ that are responsible for these elevated observations are located in coastal-terrestrial and/or coastal-seawater regions in Tasmania and the south-eastern Australian mainland. Elevated levels of CH₂Cl₂ (up to 70 ppt above background) are associated mainly with emissions from the Melbourne/Port Phillip region, a large urban/industrial complex (population 3.5 million) 300 km north of Cape Grim.Now at the Centre for Atmospheric ChemistryNow at School of Environmental Sciences     

Effect of temperature on the methyl chloride production rate in a marine phytoplankton, <Emphasis Type="Italic">Phaeodactylum tricornutum</Emphasis>

Methyl halides such as methyl chloride (CH₃Cl) are known to be important carriers of halogen from the ocean to the atmosphere, and the halogens they release into the stratosphere by photolysis catalyze ozone depletion. Marine phytoplankton have been reported as a source of CH₃Cl, but the effects of environmental temperature on the CH₃Cl production by phytoplankton have not been investigated. In this study, we investigated the effects of temperature on the production of CH₃Cl in the culture of a marine diatom, Phaeodactylum tricornutum CCMP 630, incubated at 10, 15, 20, 25, and 30 °C. CH₃Cl concentrations in cultured samples were determined using purge and trap gas chromatograph–mass spectrometry. Phytoplankton growth was monitored by measuring the chlorophyll a concentrations. CH₃Cl production was observed for several weeks at four different temperatures ranging from 10 to 25 °C. The CH₃Cl production from P. tricornutum was increased with increasing temperature from 10 to 25 °C, and the maximum production rate for CH₃Cl was 0.21~0.26 μmol (g chlorophyll a)^?1 d^?1 at 25 °C, which was several times higher than that at 10 °C (~0.03 μmol (g chlorophyll a)^?1 d^?1). The Arrhenius equation was successfully used to characterize the effects of temperature on the production rates of CH₃Cl in the culture of P. tricornutum. Our results suggest that water temperature directly affects CH₃Cl production derived from P. tricornutum and that water temperature would be a significant factor for estimating the emissions of CH₃Cl from marine environments.     

Measurement of the photodissociation coefficient of NO2 in the atmosphere: II,stratospheric measurements

The photodissociation coefficient of NO₂, J _{NO 2}, has been measured from a balloon platform in the stratosphere. Results from two balloon flights are reported. High Sun values of J _{NO 2} measured were 10.5±0.3 and 10.3±0.3×10^-3 s^-1 at 24 and 32 km respectively. The decrease in J _{NO 2} at sunset was monitored in both flights. The measurements are found to be in good agreement with calculations of J _{NO 2} using a simplified isotropic multiple scattering computer routine.     

The distribution of acetaldehyde in the lower troposphere during TROPOZ II

A series of 72 measurements of the acetaldehyde (CH₃CHO) mixing ratio were made in the lower troposphere during TROPOZ II. These measurements are the first ever made of the background level of this trace gas in the free troposphere. The data show a vertical decrease of the CH₃CHO mixing ratio with increasing altitude and indicate higher CH₃CHO concentrations in the Northern Hemisphere — in general agreement with a model-derived average CH₃CHO distribution. Deviations of the observed CH₃CHO mixing ratios from the modelled mean distribution are correlated with similar deviations in the corresponding HCHO mixing ratios.     

Chemistry–Climate Interactions of Stratospheric and Mesospheric Ozone in EMAC Long-Term Simulations with Different Boundary Conditions for CO2, CH4, N2O,and ODS

Abstract

To evaluate future climate change in the middle atmosphere and the chemistry–climate interaction of stratospheric ozone, we performed a long-term simulation from 1960 to 2050 with boundary conditions from the Intergovernmental Panel on Climate Change A1B greenhouse gas scenario and the World Meteorological Organization Ab halogen scenario using the chemistry–climate model ECHAM5/MESSy Atmospheric Chemistry (EMAC). In addition to this standard simulation we performed five sensitivity simulations from 2000 to 2050 using the rerun files of the simulation mentioned above. For these sensitivity simulations we used the same model setup as in the standard simulation but changed the boundary conditions for carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and ozone-depleting substances (ODS). In the first sensitivity simulation we fixed the mixing ratios of CO₂, CH₄, and N₂O in the boundary conditions to the amounts for 2000. In each of the four other sensitivity simulations we fixed the boundary conditions of only one of CO₂, CH₄, N₂O, or ODS to the year 2000.

In our model simulations the future evolution of greenhouse gases leads to significant cooling in the stratosphere and mesosphere. Increasing CO₂ mixing ratios make the largest contributions to this radiative cooling, followed by increasing stratospheric CH₄, which also forms additional H₂O in the upper stratosphere and mesosphere. Increasing N₂O mixing ratios makes the smallest contributions to the cooling. The simulated ozone recovery leads to warming of the middle atmosphere.

In the EMAC model the future development of ozone is influenced by several factors. 1) Cooler temperatures lead to an increase in ozone in the upper stratosphere. The strongest contribution to this ozone production is cooling due to increasing CO₂ mixing ratios, followed by increasing CH₄. 2) Decreasing ODS mixing ratios lead to ozone recovery, but the contribution to the total ozone increase in the upper stratosphere is only slightly higher than the contribution of the cooling by greenhouse gases. In the polar lower stratosphere a decrease in ODS is mainly responsible for ozone recovery. 3) Higher NO_x and HO_x mixing ratios due to increased N₂O and CH₄ lead to intensified ozone destruction, primarily in the middle and upper stratosphere, from additional NO_x; in the mesosphere the intensified ozone destruction is caused by additional HO_x. In comparison to the increase in ozone due to decreasing ODS, ozone destruction caused by increased NO_x is of similar importance in some regions, especially in the middle stratosphere. 4) In the stratosphere the enhancement of the Brewer-Dobson circulation leads to a change in ozone transport. In the polar stratosphere increased downwelling leads to additional ozone in the future, especially at high northern latitudes. The dynamical impact on ozone development is higher at some altitudes in the polar stratosphere than the ozone increase due to cooler temperatures. In the tropical lower stratosphere increased residual vertical upward transport leads to a decrease in ozone.     

The vertical sulfur dioxide distribution at the tropopause level

In 1978–1980 nine aircraft flights to an altitude of up to 15 km were made over western Europe. Sulfur dioxide was measured with a sensitive chemiluminescence method consisting of separate sampling and analysis stages and application of a wet chemical filter procedure (detection limit: 8 pptv SO₂).The measurements performed in the upper troposphere and lower stratosphere lead to some unexpected results: (a) the meteorological conditions at the tropopause level have an important influence on the observed SO₂ mixing ratio; (b) between the 500 mb and the actual tropopause level the SO₂ mixing ratio is found to be <100 pptv, and weak vertical gradients of SO₂ suggest only a small flux of tropospheric SO₂ into the stratosphere; (c) increasing SO₂ mixing ratios within the first kilometers of the stratosphere give strong support to a stratospheric source of SO₂.In the light of improved one-dimensional models considering the vertical distribution of stratospheric sulfur compounds (Crutzen, 1981; Turco et al. 1981) it can be shown that the oxidation of organic sulfur compounds (e.g., OCS, CS₂) seems to be a stratospheric source of SO₂. Furthermore, the flux calculations based on the SO₂ mixing ratios measured at the tropopause level indicate that the contribution of tropospheric (man-made) SO₂ to the stratospheric aerosol layer is of only minor importance.     

我国东部夏季一次强对流活动过程中对流层上部大气成分变化的分析

利用星载微波临边遥感探测结果,对2006年6月28～29日江淮地区的一次强对流天气过程中对流层上部一氧化碳 (CO) 、臭氧 (O₃) 、水汽 (H₂O) 和冰水含量 (IWC) 的分布特点进行了研究.强对流天气过程前后的对比分析表明,CO混合比增大,在200 hPa处增加了0.12 ppm (1 ppm=10-6);O₃混合比减小,在70 hPa处减少了0.30 ppm;H₂O混合比在250 hPa处增加了400 ppm;IWC在强降水发生之前有大幅增长,在200 hPa处最大含量可达0.03 g/m3.CO和O₃含量与垂直运动速度两者的相关变化表明,对流垂直输送作用可能是造成对流层上层和平流层低层大气成分变化的机制之一.而H₂O和IWC含量的增加主要局限于对流层顶以下,这表明对流层上部水物质的质量和形态是由垂直输送作用和对流系统内部的微物理过程共同决定的.     

On the temporal variance of stratospheric trace gas concentrations

The relative variances in stratospheric observations of longlived trace gases CH₄, N₂O, CF₂Cl₂, CFCl₃ show large differences. These differences are greatly reduced when the local mean standard deviation is normalized to the local vertical gradient. This ratio, called ‘equivalent displacement height’ exhibits a characteristic vertical profile which is very similar for all the longlived trace gases, as well as for O₃. With the help of this ratio, it is demonstrated that the variances are essentially due to natural causes, i.e., transport. Using the mixing length hypothesis a theoretical expression for the equivalent displacement height is derived. From it the meridional slope of the mixing surfaces and the mixing length can be calculated as function of the altitude. Additional information is obtained on the variance of that slope. The uncertainty of the measured mean trace gas profiles is defined.     

AGAGE Observations of Methyl Bromide and Methyl Chloride at Mace Head, Ireland, and Cape Grim, Tasmania, 1998–2001

In situ AGAGE GC-MS measurements of methyl bromide (CH₃Br) and methyl chloride (CH₃Cl) at Mace Head, Ireland and Cape Grim, Tasmania (1998–2001) reveal a complex pattern of sources. At Mace Head both gases have well-defined seasonal cycles with similar average annual decreases of 3.0% yr⁻¹ (CH₃Br) and 2.6% yr⁻¹ (CH₃Cl), and mean northern hemisphere baseline mole fractions of 10.37 ± 0.05 ppt and 535.7 ± 2.2 ppt, respectively. We have used a Lagrangian dispersion model and local meteorological data to segregate the Mace Head observations into different source regions, and interpret the results in terms of the known sources and sinks of these two key halocarbons. At Cape Grim CH₃Br and CH₃Cl also show annual decreases in their baseline mixing ratios of 2.5% yr⁻¹ and 1.5% yr⁻¹, respectively. Mean baseline mole fractions were 7.94 ± 0.03 ppt (CH₃Br) and 541.3 ± 1.1 ppt (CH₃Cl). Although CH₃Cl has astrong seasonal cycle there is no well-defined seasonal cycle in the Cape Grim CH₃Br record. The fact that both gases are steadily decreasing in the atmosphere at both locations implies that a change has occurred which is affecting a common, major source of both gases (possibly biomass burning) and/or their major sink process (destruction by hydroxyl radical).     

Trace gas measurements during aircraft flights in the tropopause region over Europe and North Africa

During aircraft flights in May 1981 from Munich (40°N) to north of the Spitsbergen Islands (82°N) and to Monrovia, Liberia (6°N), air samples were obtained in the altitude range of 8 to 11 km and during the ascents and descents near the airports. These samples have been analyzed for the trace gas mixing ratios of CH₄, CO and N₂O. The results of these analyses are presented and discussed.The results provide new evidence of tropospheric-stratospheric exchange events in the vicinity of the subpolar and subtropical tropopause foldings and possibly show a case of transport of CO-enriched air in the upper troposphere above the North Atlantic Ocean.     

In situ Measurement of H2O and CH4 with Telecommunication Laser Diodes in the Lower Stratosphere: Dehydration and Indication of a Tropical Air Intrusion at Mid-Latitudes

Telecommunication laser diodes emitting near 1.39 m and 1.65 m in combination with direct-differential absorption spectroscopy are efficient tools to monitor in situ stratospheric H₂O andCH₄ with a good precision error (a few percents), a high temporal resolution (ranging from 10 ms to 1 s), a large dynamic range in the concentration measurements (four orders of magnitude) and a high selectivity in the analyte species. To illustrate the capability of laser probing technique, we report balloonborne H₂Oand CH₄ simultaneous measurements obtained on October 2001 atmidlatitudes (43° N). The H₂O vertical profile achieved with the lasersensor in the lower stratosphere is compared with the H₂O data yielded by a balloonborne frost-point hygrometer. The total hydrogen mixing ratio in the lower stratosphere, 2[CH₄] + [H₂O], appears to beconstant at 7.5 ± 0.1 ppmv. Nevertheless, an unexpected largedehydration of 0.5 ppmv was detected by both the laser sensor and thehygrometer between 16 km and 23 km. We suspect the occurrence of a tropicalair intrusion into mid-latitudes. We support this interpretation using a high-resolution advection model for potential vorticity.     

Emission estimates of methyl chloride from industrial sources in China based on high frequency atmospheric observations

Methyl Chloride (CH₃Cl) is a chlorine-containing trace gas in the atmosphere contributing significantly to stratospheric ozone depletion (Carpenter et al. 2014). In the global CH₃Cl budget, the atmospheric CH₃Cl emissions is predominantly maintained by natural sources, of which magnitudes have been relatively well-constrained. However, significant uncertainties still remain in the CH₃Cl emission strengths from anthropogenic sources. High-frequency and high-precision in situ measurements of atmospheric CH₃Cl concentrations obtained since 2008 at Gosan station (a remote background site in the East Asia) reveal significant pollution events superimposed on the seasonally varying regional background levels. Back trajectory statistics showed that air masses corresponding to the observed CH₃Cl enhancement largely originated from regions of intensive industrial activities in China. Based on an inter-species correlation method, estimates of CH₃Cl emissions from manufacturing industries including coal combustion, use of feedstocks, or process agents in chemical production for China (2008–2012) are 297 ± 71 Gg yr.^?1 in 2008 to 480 ± 99 Gg yr.^?1 in 2009, followed by a gradual decrease of about 25% between 2009 and 2012 (398 ± 92 Gg yr.^?1 for 2010; 286 ± 68 Gg yr.^?1 for 2011; 358 ± 92 Gg yr.^?1 for 2012). The annual average of industrial CH₃Cl emissions for 2008–2012 (363 ± 85 Gg yr.^?1) in China is comparable to the known total global anthropogenic CH₃Cl emissions accounting only for coal combustion and indoor biofuel use. This may suggest that unless emissions from the chemical industry are accounted for, global anthropogenic emissions of CH₃Cl have been substantially underestimated. In particular, since industrial production and use of CH₃Cl have not been regulated under the Montreal Protocol (MP) or its successor amendments, continuous monitoring of Chinese CH₃Cl outflow is important to properly evaluate its anthropogenic emissions.     

Chlorine-hydrocarbon photochemistry in the marine troposphere and lower stratosphere

A one-dimensional photochemical model was used to explore the role of chlorine atoms in oxidizing methane and other nonmethane hydrocarbons (NMHCs) in the marine troposphere and lower stratosphere. Where appropriate, the model predictions were compared with available measurements. Cl atoms are predicted to be present in the marine troposphere at concentrations of approximately 10³ cm^-3, mostly as a consequence of the reaction of OH with HCl released from sea spray. Despite this low abundance, our results indicate that 20 to 40% of NMHC oxidation in the troposphere (0–10 km) and 40 to 90% of NMHC oxidation in the lower stratosphere (10–20 km) is caused by Cl atoms. At 15 km, NMHC-Cl reactions account for nearly 80% of the PAN produced.The model was also used to test the longstanding hypothesis that NOCl is an intermediate to HCl formation from sea salt aerosols. It was found that the NOCl concentration required (10 ppt) would be incompatible with field observations of reactive nitrogen and ozone abundance. Chlorine nitrate (ClONO₂) and methyl nitrate (CH₃ONO₂) were shown to be minor components of the total NO _y abundance. Heterogeneous reactions that might enhance photolysis of halocarbons or convert ClONO₂ to HOCl or Cl₂ were determined to be relatively unimportant sources of Cl atoms. Specific and reliable measurements of HCl and other reactive chlorine species are needed to better assess their role in tropospheric chemistry.     

Measurements of stratospheric NO2 profiles using a gas correlation radiometer in the solar occultation mode

Compact two-channel IR radiometers for solar occultation experiments have been constructed in order to measure concentration profiles of stratospheric trace gases. The instruments can be used as filter-or gas correlation-type radiometers depending on the trace gas under investigation. Within the LIMS correlative measurement program, balloon flights were performed with a payload of up to four of these two-channel radiometers. From the gas correlation-type measurements, profiles of the trace gas NO₂ are inferred for the altitude region between about 20 km and the balloon float level. The data evaluation also includes a comprehensive analysis of the error sources and their effect on the accuracy of the NO₂ profiles. The derived profiles are compared among themselves and are assessed against the observations of other authors by accounting for the diurnal, latitudinal and seasonal changes of NO₂. As a by-product of our measurements, the mean absorption of the O₂ collision-induced band at 6.4 m was determined within the range of the interference filter used and compared with calculations based on known absorption coefficients.     

Stratospheric response to chemical perturbations

The paper presents a coupled chemical-radiative one-dimensional model which is used to assess the steady-state and time-dependent composition and temperature changes in relation to the release in the atmosphere of chemicals such as CO₂, N₂O, CH₄, NO _x and chlorofluorocarbons.The model indicates that a doubling in CO₂ leads to an increase in temperature of 12.7 K near the stratopause and to an increase in total ozone of 3.3% with a local enhancement of 17% at 40 km altitude. Additional release of N₂O leads to an ozone reduction in the middle stratosphere. The reduction in the ozone column is predicted to be equal to 8.8% when the amount of N₂O is doubled. The chemical effect of CH₄ on ozone is particularly important in the troposphere. A doubling in the mixing ratio of this gas enhances the O₃ concentration by 11% at 5 km. The predicted increase of the ozone column is equal to 1.4%. A constant emission of CFCl₃ (230 kT/yr) and CF₂Cl₂ (300 kT/yr) leads to a steady-state reduction in the ozone column of 1.9% compared to the present-day situation. The effect of some uncertainties in the chemical scheme as well as the impact of a high chlorine perturbation are briefly discussed.Finally the results of a time dependent calculation assuming a realistic scenario for the emission of chemical species are presented and analyzed.     

Aircraft measurements of oxides of nitrogen along the eastern rim of the Asian continent: Winter observations

Aircraft observations of oxides of nitrogen (NO _y ), measured with a ferrous sulfate converter, over the sea surrounding the Japanese islands (30–43° N, 131–141° E) were carried out in the winter of 1983 and 1984 at altitudes mostly between 3 and 8 km. NO _y defined here is the sum of NO, NO₂, and other unstable oxides of nitrogen that are converted to NO by ferrous sulfate. The main observations were:

1. Over the Pacific Ocean between the latitudes of 30–35° N, the observed NO _y mixing ratio between 3 and 8 km was a fairly constant 200 pptv. The NO mixing ratio increased with altitude from 15 pptv at 3 km to 35 pptv at 7 km.
2. Over the Sea of Japan, tropospheric NO _y mesured between 1 and 6 km started increasing with latitude North of 35° N and reached about 1000 pptv at 40° N.
3. NO _y was measured in an air mass transported from the stratosphere near a tropopause fold region. When the ozone mixing ratio was between 80 and 140 ppbv, the NO _y mixing ratio was about 200 pptv.

     

MANTRA ‐ A Balloon Mission to Study the Odd‐Nitrogen Budget of the Stratosphere

Abstract

The Middle Atmosphere Nitrogen TRend Assessment (MANTRA) series of high‐altitude balloon flights is being undertaken to investigate changes in the concentrations of northern hemisphere mid‐latitude stratospheric ozone, and of nitrogen and chlorine compounds that play a role in ozone chemistry. Four campaigns have been carried out to date, all from Vanscoy, Saskatchewan, Canada (52°01'N, 107°02'W, 511.0 m). The first MANTRA mission took place in August 1998, with the balloon flight on 24 August 1998 being the first Canadian launch of a large high‐altitude balloon in about fifteen years. The balloon carried a payload of instruments to measure atmospheric composition, and made measurements from a float altitude of 32–38 km for one day. Three of these instruments had been flown on the Stratoprobe flights of the Atmospheric Environment Service (now the Meteorological Service of Canada) in the 1970s and early 1980s, providing a link to historical data predating the onset of mid‐latitude ozone loss.

The primary measurements obtained from the balloon‐borne instruments were vertical profiles of ozone, NO₂, HNO₃, HCl, CFC‐11, CFC‐12, N₂O, CH₄, temperature, and aerosol backscatter. Total column measurements of ozone, NO₂, SO₂, and aerosol optical depth were made by three ground‐based spectrometers deployed during the campaign. Regular ozonesonde and radiosonde launches were also conducted during the two weeks prior to the main launch in order to characterize the local atmospheric conditions (winds, pressure, temperature, humidity) in the vicinity of the primary balloon flight. The data have been compared with the Model for Evaluating oZONe Trends (MEZON) chemical transport model, the University of California at Irvine photochemical box model, and the Canadian Middle Atmosphere Model (CMAM) to test our current understanding of model photochemistry and mid‐latitude species correlations. This paper provides an overview of the MANTRA 1998 mission, and serves as an introduction to the accompanying papers in this issue of Atmosphere‐Ocean that describe specific aspects and results of this campaign.     

Measurements of stratospheric HO2 and NO2 by matrix isolation and ESR spectroscopy

Vertical profiles of stratospheric HO₂ and NO₂ concentrations were determined using matrix isolation and ESR. Up to 10 different samples per flight were collected in situ by a balloon borne cryosampler. Free radicals and trace constituents which are condensable at 68 K are trapped in a polycristalline H₂O or D₂O matrix. After collection, the samples are stored at a temperature below 83 K until they are analysed in the laboratory by X-band ESR spectroscopy at 4 K. The HO₂ and NO₂ were identified and calibrated by comparison with standard samples collected in the laboratory under typical stratospheric sampling conditions. From several flights over Southern France (44°N) we obtained two profiles of the stratospheric NO₂ mixing ratio. One, from 21 October 1982, agrees well with previous measurements. The other, from 8 October 1981, is lower by one order of magnitude. The few HO₂ data obtained around 35 km altitude agree with previous measurements. An isolated measurement at 17 km altitude is one order of magnitude higher than the model predicted HO₂ concentration.