Ozone Partial Pressure Research Articles

Facile Ozonation of Light Alkanes to Oxygenates with High Atom Economy in Tunable Condensed Phase at Ambient Temperature.

We have demonstrated the oxidation of mixed alkanes (propane, n-butane, and isobutane) by ozone in a condensed phase at ambient temperature and mild pressures (up to 1.3 MPa). Oxygenated products such as alcohols and ketones are formed with a combined molar selectivity of >90%. The ozone and dioxygen partial pressures are controlled such that the gas phase is always outside the flammability envelope. Because the alkane-ozone reaction predominantly occurs in the condensed phase, we are able to harness the unique tunability of ozone concentrations in hydrocarbon-rich liquid phases for facile activation of the light alkanes while also avoiding over-oxidation of the products. Further, adding isobutane and water to the mixed alkane feed significantly enhances ozone utilization and the oxygenate yields. The ability to tune the composition of the condensed media by incorporating liquid additives to direct selectivity is a key to achieving high carbon atom economy, which cannot be achieved in gas-phase ozonations. Even in the liquid phase, without added isobutane and water, combustion products dominate during neat propane ozonation, with CO2 selectivity being >60%. In contrast, ozonation of a propane+isobutane+water mixture suppresses CO2 formation to 15% and nearly doubles the yield of isopropanol. A kinetic model based on the formation of a hydrotrioxide intermediate can adequately explain the yields of the observed isobutane ozonation products. Estimated rate constants for the formation of oxygenates suggest that the demonstrated concept has promise for facile and atom-economic conversion of natural gas liquids to valuable oxygenates and broader applications associated with C-H functionalization.

Ozone depletion in the Arctic and Antarctic stratosphere induced by wildfire smoke

Abstract. A record-breaking stratospheric ozone loss was observed over the Arctic and Antarctica in 2020. Strong ozone depletion occurred over Antarctica in 2021 as well. The ozone holes developed in smoke-polluted air. In this article, the impact of Siberian and Australian wildfire smoke (dominated by organic aerosol) on the extraordinarily strong ozone reduction is discussed. The study is based on aerosol lidar observations in the North Pole region (October 2019–May 2020) and over Punta Arenas in southern Chile at 53.2∘ S (January 2020–November 2021) as well as on respective NDACC (Network for the Detection of Atmospheric Composition Change) ozone profile observations in the Arctic (Ny-Ålesund) and Antarctica (Neumayer and South Pole stations) in 2020 and 2021. We present a conceptual approach on how the smoke may have influenced the formation of polar stratospheric clouds (PSCs), which are of key importance in the ozone-depleting processes. The main results are as follows: (a) the direct impact of wildfire smoke below the PSC height range (at 10–12 km) on ozone reduction seems to be similar to well-known volcanic sulfate aerosol effects. At heights of 10–12 km, smoke particle surface area (SA) concentrations of 5–7 µm2 cm−3 (Antarctica, spring 2021) and 6–10 µm2 cm−3 (Arctic, spring 2020) were correlated with an ozone reduction in terms of ozone partial pressure of 0.4–1.2 mPa (about 30 % further ozone reduction over Antarctica) and of 2–3.5 mPa (Arctic, 20 %–30 % reduction with respect to the long-term springtime mean). (b) Within the PSC height range, we found indications that smoke was able to slightly increase the PSC particle number and surface area concentration. In particular, a smoke-related additional ozone loss of 1–2 mPa (10 %–20 % contribution to the total ozone loss over Antarctica) was observed in the 14–23 km PSC height range in September–October 2020 and 2021. Smoke particle number concentrations ranged from 10 to 100 cm−3 and were about a factor of 10 (in 2020) and 5 (in 2021) above the stratospheric aerosol background level. Satellite observations indicated an additional mean column ozone loss (deviation from the long-term mean) of 26–30 Dobson units (9 %–10 %, September 2020, 2021) and 52–57 Dobson units (17 %–20 %, October 2020, 2021) in the smoke-polluted latitudinal Antarctic belt from 70–80∘ S.

A case analysis of turbulence characteristics and ozone perturbations over eastern China

Our knowledge of the vertical variabilities in turbulence and ozone perturbation in the free atmosphere is severely limited because of the scarcity of high-resolution observation data. Based on the Thorpe method, a new set of sounding data in Shanghai, China, was used herein to analyze the distributions of turbulence and ozone perturbation. The region in which turbulence activity is relatively frequent spans from 5-15 km in the middle and upper troposphere. Due to the combined action of large wind shear and thermal convection, the low-troposphere stratification conditions are conducive to the generation of large-scale turbulence. Turbulence has a certain effect on atmospheric ozone concentration exchanges; in most regions located near turbulence, ozone partial pressure perturbations occur. In the troposphere, the ozone profile is most influenced by atmospheric static instability, while in the stratosphere, both wind shear and thermal convection play important roles in the emergence of ozone perturbations.

A Study of the Vertical Distribution and Sub-Peaks of Ozone below 12 km over Wuyishan Region Based on Ozone Sounding in Winter

An understanding of the vertical distribution of ozone is critical to assessing the ozone variabilities both in the stratosphere and the troposphere. We collected the profiles of atmospheric ozone partial pressure and ozone volume mixing ratio (VMR) by a sounding system at the Wuyi Mountain National Meteorological Observation Station (Shaowu sounding station 58725) from November 2021 to February 2022. In this study, the vertical distribution and sub-peak phenomenon of tropospheric ozone below 12 km are investigated using mathematical statistics and synthetic analysis. The results show that the ozone partial pressure decreased from the ground to the tropopause, which is consistent with the temperature profile. However, 66.7% of cases first showed an increasing trend from the ground to about 3 km, while there were one or more temperature inversions in the corresponding temperature profiles and the atmosphere was stable and the relative humidity was high; then, in the stratosphere, the ozone partial pressure began to increase significantly, The ozone partial pressure reaches its maximum at an average height of 24.9 km, and the maximum value was 14 mPa. The ozone VMR in troposphere is the fluctuating increase from the ground to the tropopause, and 83.3% of the cases begin to rise rapidly at about 2–5 km away from the tropopause, and the ozone surge height is 2.9 km lower than the tropopause on average. Some of these tropopause ozone VMR have shown the characteristics of stratospheric ozone. The sub-peaks of tropospheric ozone below 12 km has four cases. All the sub-peaks occur between 6.7 km and 11.5 km vertically, and peak ozone VMR is 1.6–1.9 times larger than that of the average state at the same height. The maximum stratospheric ozone VMR is 8649 ppb on average, occurring at an average height of 31.3 km, and this average height of the maximum stratospheric ozone VMR is 6.4 km higher than that for the ozone partial pressure. The total ozone in the boundary layer (0–1.5 km) is 4.3 DU on average, accounting for 1.5% in total ozone column. The total ozone in the troposphere is 39.5 DU, accounting for 13.1% in total ozone column, and the total ozone in the stratosphere is 262.4 DU, accounting for 86.9% in total ozone column.

Multi-spectral investigation of ozone: Part I. Setup & uncertainty budget

This is the first in a series of two papers concerned with new accurate high resolution spectroscopic measurements of line positions and intensities of ozone in the 5 µm and 10 µm regions using a commercial Michelson Fourier transform spectrometer. Measurements in both wavelength regions have been made quasi simultaneously using a special H-shaped absorption cell with two parallel absorption paths of different lengths that remained connected during the experiments. Accurate ozone partial pressures were monitored on the shorter of the two paths using UV absorption at the 253.65 nm Hg reference line. In this paper, we report in detail on the experimental setup and provide a comprehensive uncertainty analysis. The spectral analysis and retrieved line parameters are provided in the second paper, which also contains the comparison to the literature data. Line positions have been measured with standard uncertainties of u(ν0)=3·10−5 cm-1 in both spectral regions, mainly in the ν3 and the ν1+ν3 bands of ozone. Intensities of most of the transitions in the ν3 band have a relative standard uncertainty of ur(S)=1.1·10−2. The uncertainty is slightly smaller for intensities in the ν1+ν3 band at 5 µm. The highly accurate experimental data provide a benchmark for molecular calculations and the 1.1 % line intensity uncertainty will help resolving the discrepancy between UV and IR atmospheric ozone retrievals and correcting current biases in spectroscopic databases.

Study on the synergistic oxidation of sulfite solution by ozone and oxygen: Kinetics and mechanism

Kinetics for the synergistic oxidation of sulfite containing solution by ozone and oxygen was studied in this work. A model including the macro oxidation of sulfite solution, the gas–liquid mass transfer of ozone and oxygen, and chemical reaction in the liquid phase was developed and established. The model considered the following variables: sulfite concentration, partial pressure of ozone or oxygen, pH of the sulfite solution, ionic strength of the medium, reaction temperature, and residence time. For the oxidation processes, mass transfer of oxygen was found to be the rate-determining step as the transfer of ozone and chemical transformation was found to proceed rapidly. In addition, the simulation results for the oxidation rates obtained from this model via comparison of the experimental results with the predicted values were found to be acceptable. The developed kinetic model is beneficial for further understanding of the oxidation mechanism of sulfite solution.

Deep stratospheric intrusion and Russian wildfire induce enhanced tropospheric ozone pollution over the northern Tibetan Plateau

By using ozonesonde measurements during July–August in 2016, 2019, and 2020 at Golmud and Qaidam, European Centre for Medium-Range Weather Forecasts (ECMWF) next-generation reanalysis ERA5 data, satellite-borne Moderate Resolution Imaging Spectrometer data products, and backward trajectory calculations from the chemical Lagrangian model of the stratosphere (CLaMS) model, this study analyzes vertical ozone distributions and explores the influence of deep stratospheric intrusions and wildfires on ozone variation in the northern Tibetan Plateau (TP) during the Asian summer monsoon period. Large ozone partial pressures were observed between 20 and 30 km, with a maximum of ~16 mPa at approximately 27 km latitude. The comparisons between the vertical ozone profiles with and without the occurrence of stratospheric intrusions showed that their relative ozone difference was up to 72.4% in the tropopause layer (15.8 km), and a secondary maximum of 66.7% existed in the middle troposphere (10.1 km). The stratospheric intrusions dried the atmosphere by 52.9% and enhanced the ozone columns by 26.1% below the upper troposphere and lower stratosphere. A case study of deep stratospheric intrusion exhibited the occurrence of large ozone partial pressure in the middle troposphere in detail, with an ozone peak of ~6 mPa at 10 km, which was caused by a tropopause fold associated with the westerly wind jet at the north flank of the Asian summer monsoon anticyclone. The stratospheric intrusion processes effectively transported the cold and dry air mass with high ozone in the stratosphere downward to the middle troposphere over the northern TP. This study also confirmed that by long-range transport processes, large wildfire smoke occurred around central and eastern Russia on 19–26 July 2016 greatly caused ozone pollution in the troposphere (6 km depth from the surface) over the northern TP.

Improving ECC Ozonesonde Data Quality: Assessment of Current Methods and Outstanding Issues

AbstractWe review the current state of knowledge of ozonesonde uncertainty and bias, with reference to recent developments in laboratory and field experiments. In the past 20 years ozonesonde precision has improved by a factor of 2, primarily through the adoption of strict standard operating procedures. The uncertainty budget for the ozone partial pressure reading has contributions from stoichiometry, cell background current, pump efficiency and temperature, sensing solution type, and volume. Corrections to historical data for known issues may reduce biases but simultaneously introduce additional uncertainties. This paper describes a systematic approach to quantifying these uncertainties by considering the physical and chemical processes involved and attempts to place our estimates on a firm theoretical or empirical footing. New equations or tables for ozone/iodine conversion efficiency, humidity and temperature corrections to pump flow rate, and altitude‐dependent pump flow corrections are presented, as well as detailed discussion of stoichiometry and conversion efficiencies. The nature of the so‐called “background current” is considered in detail. Two other factors particularly affecting past measurements, uncertainties and biases in the pressure measurement, and the comparison of sonde profiles to spectrophotometric measurements of total column ozone, are also discussed. Several quality assurance issues remain, but are tractable problems that can be addressed with further research. This will be required if the present goal of better than 5% overall uncertainty throughout the global ozonesonde network is to be achieved.

Long-term analysis of the Antarctic total ozone zonal asymmetry by MERRA-2 and CMIP6 data

Objectives. To analyze ozone monthly mean data from the MERRA-2 reanalysis and CMIP6 model. To determine Antarctic ozone asymmetry climatology for austral spring months (September, October, November) over the 1980–2014 period. Methods. Processing and visualization of the MERRA-2, CMIP6 data on total ozone and ozone partial pressure, following analysis, interpretation, and comparison. Getting 2D (total ozone column) and 3D (ozone partial pressure) monthly mean ozone values for the zonal band (0°–90° S) at pressure levels (1000–0.1 hPa) for each month of the chosen period. Calculating climatology of the total ozone and ozone partial pressure. Comparison of model and reanalysis of results. Results. The amplitude of ozone zonal asymmetry was calculated to provide the monthly, latitudinal, longitudinal and altitudinal analysis. It is shown that the largest ozone zonal asymmetry is observed in spring, especially in October, with dominant wave-1 structure with zonal minimum over 0°–90° W, and maximum over 120°–180° E longitudinal sectors. The area with high ozone content is located at the 40°–80° S zonal band and gradually shifts to the south from September to November. The model underestimates amplitude of ozone zonal asymmetry, especially in October. Conclusions. Latitudinal mean maximums in zonal mean ozone distribution are observed over 62° S, in October over 66° S, and in November over 68° S for MERRA-2 and over 64° S, 65° S and 66° S respectively for CMIP6. The poleward shift of ozone latitude maximum continues until March with decreasing of ozone level, but in April, the shift reverses its direction to equatorward and ozone level starts to increase, however in the model this process is slower. In September the shift again becomes poleward. In the longitudinal distribution wave-1 pattern dominates with a shift of longitude ozone minimum. From September to October the shift is eastward, and from October to November westward by MERRA-2 data and only eastward by CMIP6 data. The highest difference in altitude ozone distribution is observed during October in the stratosphere between ozone zonal minimum and maximum points and reaches approximately 68% (44%) of the zonal average value at 65° S (65.4° S) by MERRA-2 (CMIP6) data. MERRA-2 profiles unlike CMIP6 one show higher location of altitudinal maximum over the zonal minimum and lower over the zonal maximum with the zonal mean in the middle. All three CMIP6 profiles have the same height of altitude maximum.

An automated method for preparing and calibrating electrochemical concentration cell (ECC) ozonesondes

Abstract. In contrast to the legacy manual method used to prepare, condition, and calibrate the electrochemical concentration cell (ECC) ozonesonde, an automated digital calibration bench similar to one developed by MeteoSwiss at Payerne, Switzerland, was established at NASA's Wallops Flight Facility and provides reference measurements of the same ozone partial pressure as measured by the ECC. The purpose of an automated system is to condition and calibrate ECCs before launching on a balloon. Operation of the digital calibration bench is simple and real-time graphs and summaries are available to the operator; all information is archived. The parameters of interest include ozone partial pressure, airflow, temperature, background current, response, and time (real and elapsed). ECCs, prepared with 1.0 % solution of potassium iodide (KI) and full buffer, show increasing partial pressure values when compared to the reference as partial pressures increase. Differences of approximately 5–6 % are noted at 20.0 mPa. Additional tests with different concentrations revealed the Science Pump Corp. (SPC) 6A ECC with 0.5 % KI solution and one-half buffer agreed closer to the reference than the 1.0 % cells. The information gained from the automated system allows a compilation of ECC characteristics, as well as calibrations. The digital calibration bench is recommended for ECC studies as it conserves resources.

Experimental study of the ultrathin oxides on SiGe alloy formed by low-temperature ozone oxidation

The ultrathin oxides (<1.2 nm) on SiGe are formed by directly oxidizing SiGe surface in 10% O3/O2 mixture in Beneq TFS 200 ALD system. The oxide compositions are characterized using X-ray photoelectron spectroscopy technology as a function of processing conditions, including oxidation time, temperature, and pressure. It is found that the oxide composition is very sensitive to ozone partial pressure. That is, under a lower pressure, Ge atoms can't be oxidized even over a long time and the oxides are pure SiOx. Until the temperature is increased to 300 °C, about 54% of the Ge atoms of the outermost atomic layer of SiGe are oxidized in the initial oxidation stage. Nevertheless, a slight increase in ozone partial pressure cause a rapid changeover to the formation of oxide mixture containing Si oxide and Ge oxide at all temperatures investigated, i.e. 100 °C–300 °C. Moreover, the oxidation rate of Ge atoms maintains almost unchanged from 100 °C to 230 °C, and decreases at 300 °C.

Observed response of stratospheric and mesospheric composition to sudden stratospheric warmings

In this study we investigate and quantify the statistical changes that occur in the stratosphere and mesosphere during 37 sudden stratospheric warming (SSW) events from 1989 to 2016. We consider changes in the in-situ ozonesonde observations of the stratosphere from four sites in the northern hemisphere (Ny-Ålesund, Sodankylä, Lerwick, and Boulder). These data are supported by Aura/MLS satellite observations of the ozone volumetric mixing ratio above each site, and also ground-based total-column O3 and NO2, and mesospheric wind measurements, measured at the Sodankylä site. Due to the long-time periods under consideration (weeks/months) we evaluate the observations explicitly in relation to the annual mean of each data set. Following the onset of SSWs we observe an increase in temperature above the mean (for sites usually within the polar vortex) that persists for >∼40 days. During this time the stratospheric and mesospheric ozone (volume mixing ratio and partial pressure) increases by ∼20% as observed by both ozonesonde and satellite instrumentation. Ground-based observations from Sodankylä demonstrate the total column NO2 does not change significantly during SSWs, remaining close to the annual mean. The zonal wind direction in the mesosphere at Sodankylä shows a clear reversal close to SSW onset. Our results have broad implications for understanding the statistical variability of atmospheric changes occurring due to SSWs and provides quantification of such changes for comparison with modelling studies.

First Reprocessing of Southern Hemisphere ADditional OZonesondes (SHADOZ) Profile Records: 3. Uncertainty in Ozone Profile and Total Column.

Reprocessed ozonesonde data from eight SHADOZ (Southern Hemisphere ADditional OZonesondes) sites have been used to derive the first analysis of uncertainty estimates for both profile and total column ozone (TCO). The ozone uncertainty is a composite of the uncertainties of the individual terms in the ozone partial pressure (PO3) equation, those being the ozone sensor current, background current, internal pump temperature, pump efficiency factors, conversion efficiency, and flow-rate. Overall, PO3 uncertainties (ΔPO3) are within 15% and peak around the tropopause (15±3km) where ozone is a minimum and ΔPO3 approaches the measured signal. The uncertainty in the background and sensor currents dominate the overall ΔPO3 in the troposphere including the tropopause region, while the uncertainties in the conversion efficiency and flow-rate dominate in the stratosphere. Seasonally, ΔPO3 is generally a maximum in the March-May, with the exception of SHADOZ sites in Asia, for which the highest ΔPO3 occurs in September-February. As a first approach, we calculate sonde TCO uncertainty (ΔTCO) by integrating the profile ΔPO3 and adding the ozone residual uncertainty, derived from the McPeters and Labow [2012] 1-σ ozone mixing ratios. Overall, ΔTCO are within ±15 DU, representing ~5-6% of the TCO. TOMS and OMI satellite overpasses are generally within the sonde ΔTCO. However, there is a discontinuity between TOMS v8.6 (1998-2004/09) and OMI (2004/10-2016) TCO on the order of 10DU that accounts for the significant 16DU overall difference observed between sonde and TOMS. By comparison, the sonde-OMI absolute difference for the eight stations is only ~4DU.

Solar proton events and stratospheric ozone depletion over northern Finland

We examine the variation of stratospheric ozone over northern Finland using ozonesonde observations from 1845 stratospheric balloon flights launched between 1989 and 2015 from near Sodankylä. The annual variation of the ozone partial pressure is examined and seasonal variations are explored and quantified. Direct links between the measured ozone partial pressure and common solar-wind parameters are also examined. A superposed-epoch analysis of the observations based on 191 solar proton events (SPEs) reveals a clear drop in the ozone partial pressure that commences following SPE-arrival at Earth. This analysis shows a reduction in stratospheric ozone in the winter/early-spring months (when the polar vortex is active over northern Finland), in contrast to summer/early-autumn months where no decrease is detected. By subtracting the natural seasonal variations in ozone partial pressure the SPE-driven reduction in ozone between 16 km and 24 km altitude is quantified. Analysis indicates that the ozone partial pressure during winter/early-spring is reduced, with a minimum reached ∼8 days following the SPE arrival. On average, the ozone partial pressure is reduced by ∼10% between 16 and 24 km altitude and takes ∼40 days to return to its previous level. To the best of our knowledge, this is the first comprehensive statistical study, on a regional basis, that provides direct, and long-term in-situ evidence for ozone depletion by SPEs in the northern hemisphere.

Tropospheric Ozone Climatology in Eastern Equatorial Africa

Tropospheric ozone climatology in eastern Equatorial Africa has been at the core of this study. Seasonal and annual tropospheric ozone distribution and variation have been investigated using SHADOZ network data from Nairobi for the period 1998-2013. Meteorological parameters including air temperature, relative humidity, atmospheric pressure as well as ozone partial pressure have permitted to provide the first comprehensible tropospheric ozone climatology over this region. Mean seasonal tropospheric ozone distribution displays two distinct peaks occurring in winter with 43 DU (July) and 46.8 DU in spring (October). Comparison of mean seasonal ozone partial pressure with relative humidity profiles shows a logarithmic trend with strong regression coefficient for ozone partial pressure (0.81<R2<0.92). Conversely relative humidity variation displays a linear trend with a weak seasonal regression (0.57<R2<0.74). Seasonal vertical tropospheric ozone variation displays two ozone peaks of 121 ppbv in JJA and 126 ppbv in SON at 100 hPa respectively. A minimum photochemical source contribution from local and neighboring countries has been noted at surface to mid latitude. Investigation of individual profiles chosen as case studies for JJA (25/07/2001) and SON (09/10/2002), to assess the origin of high tropospheric ozone concentration has been performed by using back trajectory HYSPLIT model. The strong role played by the Indian Ocean in the long range transport of easterly air mass into eastern Africa at mid and upper troposphere in both seasons has been confirmed. However mean monthly NCEP/NCAR Reanalysis model used to assess the contribution of STE (Stratospheric Tropospheric Exchange), shows a positive mean eddy divergence values during the months of June to July 2001, with evidence of high vorticity 1 sigma values occurring over the same period. In summer higher positive 1 sigma divergence as well as 1 sigma vorticity values have been noted showing stronger STE activity occurring in SON period. These parameters suggest that STE contribution to ozone enhancement in equatorial east Africa is stronger during SON than in JJA. Given the complexity of climate patterns over the equatorial region, in which Nairobi is located, the influence of ENSO (El Nino-Southern Oscillation) and QBO (Quasi Biennial Oscillation) in the STE occurrence cannot be excluded as noted by previous studies.

A seasonal climatology of the Melbourne 1965-1975 ozonesonde record

A seasonal climatology of the 1965-1975 Melbourne ozonesonde ozone profile record is presented, spanning a period when minimal stratospheric ozone chemical depletion existed and prior to adequate satellite ozone profiling. Results are presented as monthly isentropic weighted means of ozone mixing ratio and partial pressure, with associated uncertainties, plotted against potential temperature and altitude. Corrections for pump inefficiency and referencing to the current ozonesonde type are included. The general seasonal and altitudinal features of the results are consistent with our current understanding of ozone variations in the southern mid-latitudes. These results are of value to atmospheric chemical and climate change models.

On instrumental errors and related correction strategies of ozonesondes: possible effect on calculated ozone trends for the nearby sites Uccle and De Bilt

Abstract. The ozonesonde stations at Uccle (Belgium) and De Bilt (the Netherlands) are separated by only 175 km but use different ozonesonde types (or different manufacturers for the same electrochemical concentration cell (ECC) type), operating procedures, and correction strategies. As such, these stations form a unique test bed for the Ozonesonde Data Quality Assessment (O3S-DQA) activity, which aims at providing a revised, homogeneous, consistent dataset with an altitude-dependent estimated uncertainty for each revised profile. For the ECC ozonesondes at Uccle mean relative uncertainties in the 4–6 % range are obtained. To study the impact of the corrections on the ozone profiles and trends, we compared the Uccle and De Bilt average ozone profiles and vertical ozone trends, calculated from the operational corrections at both stations and the O3S-DQA corrected profiles. In the common ECC 1997–2014 period, the O3S-DQA corrections effectively reduce the differences between the Uccle and De Bilt ozone partial pressure values with respect to the operational corrections only for the stratospheric layers below the ozone maximum. The upper-stratospheric ozone measurements at both sites are substantially different, regardless of the correction methodology used. The origin of this difference is not clear. The discrepancies in the tropospheric ozone concentrations between both sites can be ascribed to the problematic background measurement and correction at De Bilt, especially in the period before November 1998. The Uccle operational correction method, applicable to both ozonesonde types used, diminishes the relative stratospheric ozone differences of the Brewer–Mast sondes in the 1993–1996 period with De Bilt to less than 5 % and to less than 6 % in the free troposphere for the De Bilt operational corrections. Despite their large impact on the average ozone profiles, the different (sensible) correction strategies do not change the ozone trends significantly, usually only within their statistical uncertainty due to atmospheric noise. The O3S-DQA corrections bring the Uccle and De Bilt ozone trend estimates for 1997–2014 closer to each other in the lower stratosphere and lower troposphere. Throughout the whole vertical profile, these trend estimates are, however, not significantly different from each other, and only in the troposphere significantly positive. For the entire Uccle observation period (1969–2014), the operational corrections lead to height-independent and consistent ozone trends for both the troposphere and the stratosphere, with rates of +2 to +3 % decade−1 and −1 to −2 % decade−1, respectively.

A seasonal climatology of the Melbourne 1965-1975 ozonesonde record

A seasonal climatology of the 1965-1975 Melbourne ozonesonde ozone profile record is presented, spanning a period when minimal stratospheric ozone chemical depletion existed and prior to adequate satellite ozone profiling. Results are presented as monthly isentropic weighted means of ozone mixing ratio and partial pressure, with associated uncertainties, plotted against potential temperature and altitude. Corrections for pump inefficiency and referencing to the current ozonesonde type are included. The general seasonal and altitudinal features of the results are consistent with our current understanding of ozone variations in the southern mid-latitudes. These results are of value to atmospheric chemical and climate change models.

Performance Evaluation of a Self-Developed Ozonesonde and Its Application in an Intensive Observational Campaign

To make a detailed test on the reliability and detection performance of the electrochemical concentra- tion cell (ECC) type ozonesonde which had been devel- oped and preliminarily evaluated by the authors, an inten- sive ozonesonde release experiment was held at two sites in Beijing and Changchun in June 2013. The results showed that the mean background current and its standard deviation were 0.03 (0.04) μA and 0.02 (0.03) μA in Bei- jing (Changchun). The average response time and its standard deviation were 27.8 s (30.4 s) and 4.0 s (3.7 s) in Beijing (Changchun). The ozone partial pressure profiles at both sites showed a central peak in the stratosphere and a side peak in the boundary layer. Large variation in ozone partial pressure was observed at the middle levels of the atmosphere (10-17 km). A more marked gradient of ozone change was observed in Beijing (3.4 mPa km -1 ) at the lower atmosphere level, as compared to that in Changchun (0.4 mPa km -1 ). The results presented in this paper indicate that this self-developed ozonesonde shows a high level of reliability and good performance. The ozonsonde is expected to play an important role in opera-

Assessing the performance of reactant transport layers and flow fields towards oxygen transport: A new imaging method based on chemiluminescence

A new, simple and precise ex-situ optical imaging method is developed which allows indirect measurement of the partial pressure of oxygen (as ozone) within fuel cell components. Images of oxygen distribution are recorded with higher spatial (∼20 μm) and time (40 ms) resolutions. This approach is applied to assess oxygen concentration across the face of a pseudo polymer electrolyte fuel cell (PEFC), with a serpentine design flow field. We show that the amount of light produced is directly proportional to the partial pressure of ozone, in the same way as the local current density in a PEFC is proportional to the partial pressure of bimolecular oxygen. Hence the simulated system provides information relevant to a PEFC with the same geometry operating at the same stoichiometric ratio. This new approach allows direct imaging of flow under lands due to pressure gradients between the adjacent channels and non-laminar flow effects due to secondary flow around U-turns. These are major discoveries of fundamental importance in guiding materials development and in validating modelling studies. We find that contrary to many simulation papers, advection is an important mechanism in both the gas diffusion layer (more properly “reactant transport layer”) and the microporous layer. Models which do not include these effects may underestimate reactant transport to the catalyst layer.