WP7 : The Open Stratospheric Environment: Impact of Biomass Burning and Volcano Activity on the Ozone and on Global Change; Halogen Budget and Trends

Nathalie Huret (University-LPC2E), Gwenaël Berthet (CNRS-LPC2E), V. Catoire (CNRS-LPC2E)

The VOLTAIRE project will allow us, thanks to the instrumentation installed and the associated modeling effort, to answer three major questions involved in the transport of volatile compounds and aerosols to the stratosphere and their fates.

Impact of the products of biomass burning on the stratosphere. In the coming years, we will be able to precisely quantify, for the first time, the impact on the upper troposphere – lower stratosphere and the stratosphere (UTLS) layer of a major anthropogenic source of chemical compounds (particularly NO2, CH4, N2O, CO, OCS, HCHO, H2O) playing an essential role in ozone chemistry: the burning of biomass whose emissions can be injected up to the lower stratosphere when they interact with convective episodes.

Indeed, our balloon measurements of these past few years lead to the strong suspicion that this emission process is the main source of the solid aerosols detected in the stratosphere globally, while the abundance of these aerosols, currently not quantified, is not taken into account in climate models. The advanced set of balloon-borne instruments available to the LPC2E as well as the new ones about to be finalized, will enable complete and unique understanding of the impact of biomass fires on the stratosphere. The SPIRALE and SPIRIT multichannel infrared spectrometers will quantify the trace compounds produced by burning, with excellent vertical resolution, precision and sensitivity.

Simultaneously, the LOAC aerosol meter, based on a new patented technology22, and in the process of commercialization, will determine the contents of both liquid and solid aerosols without ambiguity. In a completely unprecedented way, these aerosols will be able to be collected in situ (by the DUSTER instrument, collaboration with the University of Naples) and analyzed in the laboratory at ISTO by dark field transmission electron microscopy. In the next ten years, a completely novel balloon gondola dedicated to aerosols will combine these instruments with a next-generation Orbitrap mass spectrometer, with very high mass and spatial resolution, permitting a technological jump, unique worldwide, for conjoint analyses of the nature, physical properties and chemical composition of stratospheric aerosols.

Impact of volcano activity on the stratosphere. The next decade will be decisive in the sense that we will have reached the necessary observation period (between 25 and 30 years of cumulative observation) for the analysis of processes involving the volcano activity/stratosphere connection and new instruments for regular observations. By means of the frequent balloon sensor measurements by the LOAC instrument, the scientific community will finally be able:

  1. to precisely quantify the load of liquid sulfate aerosols ;
  2. to observe their spatial-temporal variability over the entire vertical axis for the first time;
  3. to correlate these variations with the intensity of volcanic eruptions to come in the next decade.

During major balloon operations, the gaseous sulfur budget in the stratosphere can be quantified by the SPIRIT instrument via the measurement of the gaseous precursors: OCS and SO2. All these observations coupled with the results obtained by ISTO via experimental simulations of magmatic degassing of sulfur and halogens will therefore help to improve the models according to various points:

  1. Is the sulfur budget associated with these aerosols correct in the stratospheric chemistry models ?
  2. Are the heterogeneous chemical processes of the stratospheric ozone properly simulated ?
  3. What is their impact on climate models ?

Finally, the joint analysis by two measurement techniques ELHYSA (frost point hygrometer) and SPIRIT (laser adsorption spectrometry) will be vital for characterizing the expected link between major volcanic eruptions and stratospheric water vapor trends, which American hygrometers have not been able to show.

Budget and trend of halogens in the stratosphere. With the proposed observation strategy, we will make an essential contribution to the understanding of the halogenated compound budget in the stratosphere in this key period where their decline has begun. Indeed, the budget and trends ofstratospheric bromine are only established globally by remote measurement by a single balloon-borne UVspectrometer (DOAS, University of Heidelberg). Our combined skills in balloon instrumentation (LPC2E) and laboratory analytical chemistry (ICARE) will allow mounting this type of UV spectrometer on a same gondola, already existing at LPC2E, along with the other technique of choice (in situ, by laser-induced fluorescence), for the coherent measurement of BrO, in order to finally answer the question of the stratospheric bromine contents. As for chlorine, our in-situ and precise observations of HCl (by SPIRALE orSPIRIT) will provide one of the main world references, both for the quantification of total stratospheric chlorine, and for the contribution of short-lived species (VSLS) to its budget and trend, as validation of the American, and possibly European, satellites.

Results of  WP 7 (2011-2014)

As initially planned in the project, a novel and unique strategy of regular observations of atmospheric aerosol has been successfully set up using an aerosol counter for the first time with light meteo balloons. With the operational support of the CNES space agency, the influence of volcanic eruptions and meteoric precipitation on the stratospheric aerosol burden and variability has been investigated as anticipated. The abundance of the main stratospheric aerosol precursor (OCS) has been measured for the first time in-situ. However, investigation of biomass burning effects on the composition of the tropical stratosphere could not be achieved due to the abandonment by CNES of its balloon launching site in the tropics. The Labex’s efforts made nevertheless possible one light balloon flight at a new valuable tropical site at La Réunion Island. In addition, the feasibility of in-situ measurements aerosol chemical composition by a new mass type of ultra-high resolution mass spectrometer (Orbitrap™) has been undertaken.

The Labex Voltaire planning for the study of the halogen budget in the stratosphere has been delayed due to the absence of flight offers by CNES in the report period. However a modelling study has shown that 10-40% of stratospheric bromine could originate from very short-lived species. Concerning dynamics, we characterized the ability of meteorological models to represent wind variability in the stratosphere using wind measurements deduced from big balloon (ZPB) trajectories obtained during the last two decades at all latitudes. The originality of this study comes from the unique wind database developed with CNES in term of altitude range (up to 2 hPa). The ECMWF Era-Interim Reanalysis systematically underestimates wind speed with increasing errors as a function of altitude. We have also investigated the ability of climate model to represent the pole-tropics coupling through the frequency of tropical intrusions at high altitude (30 km) and the occurrence of Frozen-In Anticyclones in spring season in polar region. Such transport mechanisms at large scale are very sensitive to the representation used in climate model of the Quasi Biennial Oscillation.

Results of  WP 7 (2015-2018)

During that period, we studied the interactions between the stratospheric processes and the climate with particular focus on mechanisms involving aerosols, trace gases and dynamical variability, by using unique in situ observations and model calculations.

Seasonal and long-term evolution of tropospheric emissions, linked to anthropogenic activities or natural variability, impact chemical compounds amounts and the aerosol content in the Upper Troposphere / Lower Stratosphere (UTLS) and stratosphere. Trace species in the gas phase, in the heterogeneous phase or via aerosol production, affect the ozone layer and the climate through chemical, radiative and dynamical effects which are complicated by feedback mechanisms. Uncertainties exist regarding the interplay between changes in stratospheric trace species and climate and the response in a future with increased greenhouse gases and ozone recovery. It is therefore necessary to better understand and monitor physical and chemical mechanisms which control the chemical and aerosol contents in the stratosphere.

This topic relies on novel balloon-borne and airborne instruments (developed during the course of the labex project: see Section 5) and internationally-recognized chemistry-transport models

Biomass burning in the upper troposphere and lower stratosphere (UTLS).

Stratospheric Aerosol content above India and Asia

Satellite observations have shown that Indian monsoon transports aerosols or aerosol precursors from ground pollution and from biomass burning emissions, from more or less remote sources (e.g. in China), to high altitude levels. This results in an aerosol layer (called ATAL for Asian Tropopause Aerosol Layer) located in the tropopause region, i.e. around 16-17 km which appears confined in the Asian monsoon anticyclone every summer (Vernier et al., BAMS, 2018) as shown in figure 1.

Figure 1: Aerosol scattering ratio at 532 nm observed by the CALIOP/Calipso space-borne lidar on summer 2015 in the 16-18 km altitude range. From Vernier et al. (BAMS, 2018).

LPC2E through VOLTAIRE’s support participates to balloon campaigns in India to confirm the existence of the ATAL layer and characterize in situ the physical properties of the aerosols within (figure 2). These campaigns are conducted in the frame of a NASA-ISRO (Indian Space Agency) agreement.

Figure 2: Pictures of balloons used to probe the tropopause region above India. From Vernier et al. (BAMS, 2018).

We have performed several balloon flights using the LOAC instrument in this frame. Although the balloon burst occurred at too low altitude preventing us from probing the entire range of the ATAL layer, the instrument has observed an increase in the aerosol content at the expected bottom altitudes of the ATAL layer both for particles smaller than 1 µm and bigger than 5 µm (figure 3). The increase is confirmed in the signal from simultaneous observations conducted by a backscatter sonde.

Figure 3: Vertical concentration profiles measured by the LOAC instrument on 21/08/2015 above Varanasi (25°N, 82°E) for particle sizes between 0.2 and 1 µm and bigger than 5 µm. The BSR (Backscattering Ratio) signal from the COBALD sonde is also represented. Orange circles indicate the expected position of the ATAL layer.

Further flights are planned in summer 2018. Recent results from the ground-based lidar located at Observatoire de Haute Provence indicate that the ATAL layer enhances the aerosol content over the whole Northern Hemisphere. But this detection has required some averaging over several years. This effect has never been captured by in situ observations. This will be done with LOAC when time series will be long enough to get a robust statistical analysis.

Long-range transport of biomass burning products

The Mediterranean Basin is at the crossroad of pollutant emissions from Western and Central Europe and of mineral dust from major sources in the Sahara and Arabian deserts. Several studies have also shown the occurrence over the Mediterranean Basin of long-range transport of air masses polluted by biomass burning aerosols.

During the GLAM campaign (Ricaud et al., BAMS, 2018) in August 2014, two cases of long-range intercontinental transport of biomass burning products in the free and upper troposphere over the Mediterranean Basin in August 2014 was identified with in situ measurements, and their impact was evaluated on trace gas concentrations using modelling (Brocchi et al., ACP, 2018). During two flights on 6 and 10 August 2014 (figure 4), increases in CO, O3 and aerosols were measured over Sardinia at 5.4 and 9.7 km above sea level, respectively. 20-day backward trajectories, calculated with the Lagrangian particle dispersion model FLEXPART (www.flexpart.eu), show that the air sampled by the aircraft have biomass burning origin. Biomass burning products came on 10 August from the northern American continent with air masses transported during 5 days before arriving over the Mediterranean Basin. On 6 August biomass-burning products came from Siberia with air masses travelling during 12 days and enriched in fire emission products above Canada 5 days before arriving over the Mediterranean Basin. This study was performed within the frame of the Ph.D thesis from V. Brocchi (LPC2E).

Figure 4: Flight on 10 August 2014: (a) 3D-trajectory color-coded according to CO volume mixing ratios (vmr) between Lampedusa and Toulouse. (b) (Top): Flight altitude, longitude and latitude as a function of time; (Middle): Time series of CO (black), Ozone (Yellow) and relative humidity (blue); (Bottom): Time series of aerosol concentrations (brown). (c) Picture of a dark thin layer from the Falcon-20 at an altitude of 9.7 km at 13:12 UTC. From Brocchi et al. (ACP, 2018).

Our measurements also show that long-range transport of biomass burning induces, at the local scale, an increase of O3 and CO in the upper troposphere over the Mediterranean Basin.

A similar phenomenon was also detected recently during the intense period of fires over North America during August 2017 (figure 5). This phenomenon was detected by the instrument LOAC during a balloon flight on 23 August 2017. As during GLAM campaign, the origin of air masses calculated by FLEXPART, show the transport of the biomass burning pollutant travelling the Atlantic Ocean to impact directly the stratosphere over Europe.

Figure 5: Daily Suomi NPP VIIRS true-color image composites (07-13 August), with VIIRS-detected fire locations plotted in red.

Impact of volcano activity on the stratospheric aerosol content

Natural gas sulphur precursors controlling the “background” UTLS aerosol layer

It is recognized that the aerosols in the stratosphere are dominated by the sulphur cycle. The main gas precursor of the stratospheric aerosol layer in volcanically-quiescent periods is carbonyl sulphide, OCS, emitted by oceans and which is photolyzed once it reaches stratospheric levels due to the BDC. The oxidation of OCS produces sulphate aerosols. We have been able to accurately derive the spatial distribution of OCS (figure 6) at very high vertical resolution, owing to in-situ observations by the balloon-borne SPIRALE instrument from LPC2E along with other available observations (Glatthor et al., GRL, 2015) and to derive a stratospheric sink of 49±14 Gg.S.an-1 (S for sulfur), which is in agreement with values implemented in models (Krysztofiak et al., Atmos. Ocean, 2015). The central role of OCS in the production of stratospheric aerosols at the global scale is therefore confirmed, which explains, at least partly, why models, when well-parameterized in terms of sources, fluxes, transport and photochemistry of OCS, correctly reproduce satellite observations on a zonal average basis in the low and middle stratosphere.

Figure 6: OCS partial column above 13 km with error bars (representing the 1σ measurement precisions) versus latitude (°N) from several balloon campaigns at different latitudes. From Krysztofiak et al., Atmos. Ocean, 2015.

Periods with volcanic activity

Two processes have been proposed to explain the increase in the post-2000 trend of the global aerosol content: the increase in the SO2 emissions from anthropogenic activities in Asia (coal burning) and moderate (but regular) volcanic eruptions in this period. Results indicate that the most dominant process is from volcanic eruptions which result in aerosol enhancements over periods of months to years (Jégou et al., ACP, 2013; Bègue et al., ACP, 2017), though we cannot exclude a contribution of anthropogenic SO2 to the (low frequency) increase.

LOAC instruments have been deployed to capture these volcanic events. Associating the Reunion Island (21°S) site and the LOAC flexible balloon launching capability provides a unique strategy to probe the tropical stratosphere largely located above areas dominated by the ocean which usually complicates the availability of operational facilities. This was done for instance in 2015, a year when the stratosphere was impacted by the Calbuco (Chile) volcanic eruption. As illustrated in figure 7 presenting LOAC observations to ground-based lidar and satellite data, the stratospheric aerosol content in the southern hemisphere is enhanced over a period of ~1 year due to the eruption (Bègue et al., ACP, 2017).

Figure 7: Evolution of aerosol optical depth (AOD) calculated between 17 and 30 km at 532 nm from lidar (red), LOAC OPC (blue), and OMPS (green) observations between November 2014 and November 2016 over the Reunion site. The small dots represent the daily AOD and the large dots represent the monthly averaged AOD obtained from OMPS and lidar observations. The large blue dots represent the AOD calculated from LOAC OPC observations over Reunion for several balloon flights. From Bègue et al. (ACP, 2017).

The impact of one of these eruptions (Sarychev event in June 2009) on the northern hemisphere has been quantified using space-borne observations and compared to the WACCM-CARMA Climate-Chemistry Model simulation (Jégou et al., 2013; Lurton et al., ACP, 2018). This communitary model developed in the USA has been installed at LPC2E and OSUC owing to VOLTAIRE’s support. It includes the full sulphur chemical cycle and a microphysical scheme to form aerosols from gas emissions. The spatial and temporal evolution of the SO2 plume (0.9 Tg injected by the volcano) has been compared to space-borne data from IASI (figure 8) to evaluate the capacity of the model to transport the emitted SO2 and its transformation processes to sulfate aerosols.

Figure 8: Spatial and temporal evolution of vertical column densities of SO2 (in Dobson units, DU) over 1–2 weeks following the Sarychev eruption according to IASI satellite observations (left) and simulated by the WACCM model (right). From Jégou et al. (ACP, 2013) and Lurton et al. (ACP, 2018).

One the main results of the Lurton et al.’s study (2018) is that model-satellite observations agree when the satellite data biases (problems of spatial sampling, problems of saturation for high aerosol contents) are also accounted for in the model (figure 9). Not considering satellite data biases can lead to erroneous conclusions in terms of volcanic aerosol residence times and formation/growth/removal processes.



Figure 9: Comparison of modelled and observed anomalies in stratospheric aerosol optical depth (SAOD). The absolute SAOD data have been converted to anomalies by subtracting modelled or observed SAOD 1 week before the eruption. (a) Stratospheric sulfate aerosol optical depth anomaly at 750 nm as simulated by WACCM. (b) WACCM’s stratospheric sulfate SAOD anomaly at 750 nm degraded to account for limitations in OSIRIS data (including saturation effect and minimum altitude). (c) Actual anomaly in OSIRIS SAOD retrieval obtained from data with measurement limitations. The shaded area denotes the polar night, where OSIRIS’s measurements are missing.

The Sarychev eruption is also an illustration of the capacity of volcanoes to inject halogens directly into the stratosphere with some expected consequences on stratospheric chemistry and ozone. An injection of volcanic HCl (27 Gg) has also been detected along with the typical SO2 one. The chemical effects have been investigated using the WACCM model (Lurton et al., ACP, 2018). The first effect calculated by the model deals with a slowdown of SO2 oxidation and a 2-day delay in the associated formation of sulphuric acid aerosols, a process never reported before in the stratosphere (figure 10). This is due to enhanced reaction of HCl + OH → Cl + HO2 which sequesters some OH reacting with SO2 to form aerosols.

Figure 10: Temporal evolution of total SO2 and SO4 burdens (Tg sulfur), integrated over the Northern Hemisphere over June–August 2009 (the eruption is depicted by the red triangle). Model anomalies are shown for runs with injection of SO2 only (red and yellow for SO2 and SO4, respectively) and with co-injection of HCl (green and blue for SO2 and SO4, respectively). From Lurton et al. (ACP, 2018).

Water vapour is also a gas precursor of stratospheric sulphuric acid aerosols which are typically composed of 25-40% of water. Water vapour entering the stratosphere is expected to be mainly driven by thermodynamics through tropopause temperature variability but one question is whether or not volcanic eruptions are likely to participate to some sporadic variations in the stratospheric water vapour content (figure 11) through direct injections of this compound. We have used our balloon-borne observations satellite to investigate this issue and have shown no evidence of such effect on the 1991-2012 period regularly impacted by volcanic eruptions, the water vapour variability (Berthet et al., JAC, 2013).

Figure 11: Stratospheric water vapour variations derived from HALOE and MLS space-borne instruments. Berthet et al. (JAC, 2013).

Budget and trend of halogens in the stratosphere

Injection of halogens by convective systems

The study of atmospheric degradation mechanisms for brominated very-short-lived substances (VSLS) using a regional (3D) chemistry transport model (CCATT-BRAMS) revealed that 10 to 40% of active bromine from these marine source species can reach the stratosphere under polluted conditions (Krysztofiak et al., Atmos. Env. 2012; Marécal et al., ACP 2012).

Figure 12: Vertical profiles of Br contained in CHBr3 (top left), in HBr (top right), in the total organics (bottom left), and in the total inorganics (bottom right) except HBr, on 17 November (open circle), on 20 November (open square), on 23 November (cross) and on 26 November (open triangle), for the polluted atmosphere. From Krysztofiak et al. (Atmos. Env., 2012).

These results were confirmed by in-situ aircraft measurements of convective outflow in the Malaysia region (Krysztofiak et al., ASL 2018). Correlated enhancements of CO, CH4 and the short-lived halogen species (CH3I and CHBr3) were detected when the aircraft crossed the convective systems showing 15 to 67% of the air comes from the boundary layer.

Figure 13: Measurements of CHBr3 and CH3I (top, GHOST instrument, Univ. of Frankfurt) and CO (bottom, SPIRIT instrument) from aboard the Falcon-20 during SHIVA campaign. Picture from the mini-DOAS webcam (U. Heidelberg) show the convective system sampled. From Krysztofiak et al. (ASL, 2018).

Halogens in the stratosphere associated with volcanic eruptions

The injection of halogens by volcanic eruption directly into the stratosphere is a rarely captured event and is of interested for stratospheric chemistry as a result of the impact of halogens on ozone depletion. No bromine injection by the Sarychev volcano has been observed. However, we have shown that the amounts of bromine species are directly affected by the volcanic aerosol and associated heterogeneous processes (figure 14). Their connection with nitrogen compounds was of significant importance in the control of stratospheric ozone chemistry under such high aerosol loading conditions (Berthet et al., ACP, 2017). For instance, we have shown that heterogeneous processes involving bromine compounds account for 25% of the ozone depletion. This work was the first study about the impact of a “moderate” volcanic eruption on stratospheric ozone chemistry.

Figure 14: Impact of the Sarychev volcanic aerosols on the stratospheric bromine content. Black: balloon-borne measurements (LPC2E and University of Heidelberg); Green: model simulation without volcanic aerosols; Blue: model simulations with volcanic aerosol loadings (from various sources of observations). From Berthet et al. (ACP, 2017).

However, the 2009 Sarychev eruption was a highly valuable case to investigate the impact of volcanically-injected chlorine on stratospheric ozone chemistry. The Lurton et al. (ACP, 2018)’s work is the first one investigating such process. NOx, reduced by 50% due to heterogeneous reactions on volcanic aerosols, are further destroyed (leading to a value of 60%) due to the direct injection of HCl by the volcano up to 16 km in altitude and the effect of added chlorine on the chemical cycles. Ozone destruction calculated to be of 5% if no volcanic chlorine injection is considered and reaches 7% is a HCl injection is accounted for (figure 15). The limited chemical impacts are due to too high temperatures in the stratosphere at the specific period of the eruption preventing from enhanced catalytic ozone destruction cycles. However, this event has allowed us to point out the main chemical mechanisms behind volcanic injection of chlorine and the framework for a bigger event in the future.

Figure 15: Zonally averaged depletions in stratospheric ozone and NO2 at midlatitudes (40 to 60°N) and high latitudes (60 to 80°N) following the Sarychev eruption. Ozone is shown in the upper set of plots, NO2 in the lower sets; within each pair, the latitudes are shown as 60 to 80°N (upper plot of the pair) and 40 to 60°N (lower plot of the pair). Simulations by the WACCM model are expressed as percentage anomalies (with respect to the volcano-off control run) and are calculated for the simulation with SO2 injection only (a, c, e, g), and simulation with co-injection of HCl (b, d, f, h).

The coupling between climate change and stratospheric dynamics

Poleward transport variability in the Northern Hemisphere during final stratospheric warmings simulated by CESM-WACCM

We set up the ENRICHED project, a “European collaboratioN for Research on stratospherIc CHEmistry and Dynamics”, funded by CNES, INSU-CNRS and VOLTAIRE. The goal was to study the Arctic stratosphere, a key-region to follow the potential modifications of the coupled chemical-dynamical system induced by the climate change. Observational studies of stratospheric vortex final warmings showed that tropical/subtropical air masses can be advected to these latitudes and remain confined within a long-lived “frozen-in” anticyclone (FrIAC) for several months. It was suggested that the frequency of FrIACs may have increased since 2000 and that their interannual variability may be modulated by the occurrence of major stratospheric warmings (SSW) in the preceding winter and the phase of the quasi-biennial oscillation (QBO). For the first time, these hypotheses were tested using a chemistry climate model. 145-years sensitivity experiments were performed with the National Center of Atmospheric Research’s (NCAR) Community Earth System Model (CESM-WACCM). The model simulated a realistic frequency and characteristics of FrIACs, which occur under an abrupt and early winter-to-summer stratospheric circulation transition, driven by enhanced planetary wave activity. Furthermore, the model results support the suggestion that the development of FrIACs is favored by an easterly QBO in the middle stratosphere and by the absence of major SSWs during the preceding winter. The lower stratospheric persistence of background dynamical state anomalies induced by deep SSWs leads to less favorable conditions for planetary waves to enter the high-latitude stratosphere in April, which in turn decreases the probability of FrIAC development. Our model results do not suggest that climate change conditions (RCP8.5 scenario) influence FrIAC occurrences (Thiéblemont et al., JGR 2016; Thiéblemont et al., JGR 2013).

Figure 16: Northern hemisphere: (left panel) potential vorticity (at 850 K potential temperature, i.e. 30 km alt.) showing the air masses of different origins (blue: tropical) as simulated by MIMOSA transport model (in collaboration with LATMOS); (right panel): consequences on ozone level (in ppm).

Assessment of the ERA-Interim Winds Using High-Altitude Stratospheric Balloons

The study, led by the Ph.D F. Duruisseau, focused on the ability of ERA-Interim model from the European Centre for Medium‐Range Weather Forecasts (ECMWF) to represent wind variability in the middle atmosphere (Duruisseau et al., JAS 2017). The originality of the proposed approach is that wind measurements are deduced from the trajectories of zero-pressure balloons that can reach high-stratospheric altitudes. The trajectories of balloons launched above Esrange (Sweden) and Teresina (Brazil) from 2000 to 2011 were used to deduce zonal and meridional wind components (by considering the balloon as a perfect tracer at high altitude). The > 1-million collected data cover several dynamical conditions associated with the winter and summer polar seasons and west and east phases of the quasi-biennial oscillation (QBO) at the equator. Systematic comparisons between measurements and ERA-Interim data were performed for the two horizontal wind components, as well as wind speed and wind direction in the 100-2 hPa pressure range to deduce biases between the model and balloon measurements as a function of altitude. Results showed that whatever the location and the geophysical conditions considered, biases between ERA-Interim and balloon wind measurements increase as a function of altitude. The standard deviation of the model–observation wind differences can attain more than 5 m/s at high altitude (pressure P < 20 hPa). A systematic ERA-Interim underestimation of the wind speed is observed and large biases are highlighted, especially for equatorial flights (Duruisseau et al., JAS 2017). This project was associated to the FP7 ARISE (Atmospheric dynamic Research Infrastructure for Europe) project.

Effect of volcanic eruptions on the stratospheric circulation

We presented evidence for the effect of volcanic aerosol on the stratospheric circulation, focusing on the Mount Pinatubo eruption in 1991 and discussing further the minor extratropical volcanic eruptions after 2008. Using a multiple linear regression technique accounting for observed stratospheric aerosol, we have shown that the observed pattern of decadal circulation change over the past decades is substantially driven by volcanic aerosol injections via calculations of mean age of air and its trends (figure 17). We reveal a strengthened tropical upwelling at upper levels (above about 22 km) and weakened tropical upwelling below. The mean age response, however, is not unambiguously linked to the tropical upwelling change and shows increasing mean age of air globally, whereas climate models typically show decreasing mean age at upper levels. Thus, we conclude that climate model simulations need to realistically take into account the effect of volcanic eruptions, including the minor eruptions after 2008, for a reliable reproduction of observed stratospheric circulation changes.

Figure 17: Altitude (km) vs latitude plot reflecting the volcanic effect on the mean age trends (in years per decade) related to the volcanic eruptions during the period 2002–2011. The figure shows increased age of air in the stratosphere resulting from these eruptions. From Diallo et al. (GRL, 2017).

Effect of gravity waves on the distribution of aerosols and tracer gases

Coupled balloon-borne observations of LOAC (figure 18 from Chane-Ming et al., ACP, 2016), M10 meteorological sondes, ozonesondes, and GPS radio occultation data, were examined to identify gravity-wave-induced fluctuations on tracer gases and on the vertical distribution of stratospheric aerosol concentrations during the 2013 ChArMEx (Chemistry-Aerosol Mediterranean Experiment) campaign. Observations revealed signatures of gravity waves with short vertical wavelengths less than 4 km in dynamical parameters and tracer constituents (e.g. ozone), which are also correlated with the presence of thin layers of strong local enhancements of aerosol concentrations in the upper troposphere and the lower stratosphere. The European Centre for Medium-Range Weather Forecasts (ECMWF) analyses also showed evidence of mesoscale inertia gravity waves with similar horizontal characteristics above the eastern part of France. Ray-tracing experiments indicate the jet-front system as the main source of these waves. This unique study reveals that mesoscale gravity waves induce a strong modulation of the amplitude of tracer gases and stratospheric aerosol background.

Figure 18: 50 m interpolated vertical profiles of aerosol concentration (cm-3) with diameters 0.2–50 μm above Minorca Island (39.99°N, 4.25°E) (a–b) on 19 June at 13:41 UTC and 28 June at 05:30 UTC respectively, and above Ile du Levant (43.02 ◦ N, 6.46 ◦ E) (c–d) on 27 July at 23:03 UTC and 3 August at 10:56 UTC during the 2013 ChArMEx campaign. From Chane-Ming et al., ACP (2016).

Instrumental development for in situ measurements of atmospheric composition

New developments for aerosol detection: the LOAC light aerosol counter

The LOAC instrument (Light Optical Particle Counter) has been developed in the frame of Ecotech ANR with industrial partners (Environnement SA and MeteoModem). It is a new light particle counter of a few hundred grams designed to operate on light meteorological balloons and on the ground. This strategy allows us to capture with high responsiveness and flexibility biomass burning plumes from the ground to the stratosphere.

A complete description of the instrument is given in Renard et al. (AMT, 2016a,b) and Vignelles et al. (2016). In brief, LOAC measures the concentration of aerosols over 19 size classes between 0.2 and 100 µm. Two scattering angles are used (figure 1): 1) for which the scattered light is mainly dependent on the particle size and weakly dependent on its refractive index. This requires a real-time correction of stray light; 2) 60° which is more typical and is both sensitive to the particle size and refractive index. The combination of both signals at the 2 angles provides some indication about the main nature (typology) of the particles.

Figure 19: LOAC and its pump (left) and optical design (right).

SPECIES: SPECtrometer with Infrared laErs in Situ

VOLTAIRE project also allowed to partly funds the development (in complement with CNES and CPER ARD FEDER PIVOTS), from scratch of a new balloon- and air-borne instrument, SPECIES, a 3-channel infrared laser spectrometer based on the coupling of state-of-the-art technologies (QCLs: quantum cascade laser, and OF-CEAS: optical feedback cavity enhanced absorption spectroscopy), enabling rapid and very accurate measurements of trace gases, among them the greenhouse gases CH4 and CO2, and the chlorine species HCl and nitrogen species (HNO3, N2O), sources of the main ozone layer destroyers. This one was ready in summer 2018 and performed a successful balloon flight (https://twitter.com/CNES/status/1030383283694186496) as a first test during the Strato-Sciences 2018 campaign from CNES and Canada Space Agency in Timmins (Canada).

Figure 20: Left panel: Optical bench for 1 channel including the QCL and the OFCEAS and their electronic and flow controls; Right panel: SPECIES inside the CNES gondola ready for balloon flight.

ORBAS: a mass spectrometer ORBITRAPTM for AeroSols

The instrument ORBAS (ORBITRAPTM for Aerosols) is currently under development at LPC2E (with VOLTAIRE and PIVOTS projects funding). The objective is to implement the high resolution mass spectrometry (HRMS) for the in situ characterization of the chemical composition of the atmospheric aerosols. The HRMS approach will allow the detailed characterization of the extremely complex mixture of organic and inorganic species composing the secondary aerosols of biogenic and anthropogenic origin. The measurements of this type are of great interest for the studies related to the formation, evolution and properties of the atmospheric aerosols. One final goal is also to conduct laboratory analyses of stratospheric aerosols collected on filters during balloon flights.

The ORBAS is essentially a modification of the commercial mass spectrometer (ORBITRAPTM Exactive, Thermo Fisher Scientific) equipped with electrospray ion source for the laboratory analysis of liquid samples. The main modifications of the instrument are the following:

  1. Introduction of a new system for the automated filter collection of aerosols and programmable evaporation of the collected particles;
  2. Replacement of the electrospray by a chemical ionisation ion source;
  3. Replacement of the existing ion transfer system consisting of a heated capillary and an electrostatic ion optics by a double radio frequency ion guide (“ion funnel”);
Figure 21: Detailed scheme of the ORBAS spectrometer (left panel) with the interface (right panel)

Expected performances:

  • Quantitative characterization of the composition of organic aerosols: organic acids, aldehydes, ozonolysis products…
  • Lower Limit of Detection (LDL): several pg / m3;
  • Time resolution of 5-10 minutes
  • Measurements with the HELIOS environmental chamber of ICARE:
    • Analysis of the aerosol formed during the ozonolysis of different terpenes and isoprene;
    • Intercomparison with other available instruments, e.g., CIMS TOF of ICARE
  • Measurements in situ on the VOLTAIRE Super Site of Orléans (validation, tests, field studies)
  • Field studies (participation in future field campaigns), inclu

Stratospheric microhygrometer

In a CNES-VOLTAIRE R&T, we are developing a new micro-hygrometer in place of ELHYSA balloon instrument, which can be embarked under zero-pressure stratospheric balloon (BSO) or meteorological balloon, or in high-altitude aircraft. The goal is to reduce the mass to less than 2.5 kg to be used on these various carriers, and to make very a low cost so loseable small instrument, while keeping the instrumental qualities of its predecessor (ELHYSA) to facilitate inter-comparisons, and increase the frequency measurement (>0.1Hz), the precision (~0.1%) and the accuracy (~1ppmv). The determination of the temperature of the frost point is performed thanks to the variation of the frost mass on a quartz blade, leading to a change in the resonance frequency of the blade.

Figure 21: Left panel: Calibration equipment in laboratory for simulation of stratospheric conditions; Right panel: detailed scheme of the sensor (measurements of the resonance frequencies modified (Q1) or not modified (Q3) by frost.



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Krysztofiak, G., V. Catoire, P. D. Hamer, V. Marécal, C. Robert, A. Engel, H. Bönisch, K. Grossman, B. Quack, E. Atlas, K. Pfeilsticker (2018). Evidence of convective transport in tropical West Pacific region during SHIVA experiment, Atmos. Sci. Lett., doi: 10.1002/asl.798.

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Krysztofiak G., Catoire V., Poulet G., Marécal V., Pirre M., Louis F., Canneaux S., Josse B. (2012). Detailed modeling of the atmospheric degradation mechanism of very-short lived brominated species. Atmospheric environment, vol 59, pp. 514-532. doi: 10.1016/j.atmosenv.2012.05.026

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