Electrochemical Concentration Cell Ozonesondes Research Articles

Trajectory matching of ozonesondes and MOZAIC measurements in the UTLS – Part 2: Application to the global ozonesonde network

Abstract. Both balloon-borne electrochemical ozonesondes and MOZAIC (measurements of ozone, water vapour, carbon monoxide and nitrogen oxides by in-service Airbus aircraft) provide very valuable data sets for ozone studies in the upper troposphere/lower stratosphere (UTLS). Although MOZAIC's highly accurate UV-photometers are regularly inspected and recalibrated annually, recent analyses cast some doubt on the long-term stability of their ozone analysers. To investigate this further, we perform a 16 yr comparison (1994–2009) of UTLS ozone measurements from balloon-borne ozonesondes and MOZAIC. The analysis uses fully three-dimensional trajectories computed from ERA-Interim (European Centre for Medium-Range Weather Forecasts Re-analysis) wind fields to find matches between the two measurement platforms. Although different sensor types (Brewer-Mast and Electrochemical Concentration Cell ozonesondes) were used, most of the 28 launch sites considered show considerable differences of up to 25% compared to MOZAIC in the mid-1990s, followed by a systematic tendency to smaller differences of around 5–10% in subsequent years. The reason for the difference before 1998 remains unclear, but observations from both sondes and MOZAIC require further examination to be reliable enough for use in robust long-term trend analyses starting before 1998. According to our analysis, ozonesonde measurements at tropopause altitudes appear to be rather insensitive to changing the type of the Electrochemical Concentration Cell ozonesonde, provided the cathode sensing solution strength remains unchanged. Scoresbysund (Greenland) showed systematically 5% higher readings after changing from Science Pump Corporation sondes to ENSCI Corporation sondes, while a 1.0% KI cathode electrolyte was retained.

Propagation of radiosonde pressure sensor errors to ozonesonde measurements

Abstract. Several previous studies highlight pressure (or equivalently, pressure altitude) discrepancies between the radiosonde pressure sensor and that derived from a GPS flown with the radiosonde. The offsets vary during the ascent both in absolute and percent pressure differences. To investigate this problem further, a total of 731 radiosonde/ozonesonde launches from the Southern Hemisphere subtropics to northern mid-latitudes are considered, with launches between 2005 and 2013 from both longer term and campaign-based intensive stations. Five series of radiosondes from two manufacturers (International Met Systems: iMet, iMet-P, iMet-S, and Vaisala: RS80-15N and RS92-SGP) are analyzed to determine the magnitude of the pressure offset. Additionally, electrochemical concentration cell (ECC) ozonesondes from three manufacturers (Science Pump Corporation; SPC and ENSCI/Droplet Measurement Technologies; DMT) are analyzed to quantify the effects these offsets have on the calculation of ECC ozone (O3) mixing ratio profiles (O3MR) from the ozonesonde-measured partial pressure. Approximately half of all offsets are > ±0.6 hPa in the free troposphere, with nearly a third > ±1.0 hPa at 26 km, where the 1.0 hPa error represents ~ 5% of the total atmospheric pressure. Pressure offsets have negligible effects on O3MR below 20 km (96% of launches lie within ±5% O3MR error at 20 km). Ozone mixing ratio errors above 10 hPa (~ 30 km), can approach greater than ±10% (> 25% of launches that reach 30 km exceed this threshold). These errors cause disagreement between the integrated ozonesonde-only column O3 from the GPS and radiosonde pressure profile by an average of +6.5 DU. Comparisons of total column O3 between the GPS and radiosonde pressure profiles yield average differences of +1.1 DU when the O3 is integrated to burst with addition of the McPeters and Labow (2012) above-burst O3 column climatology. Total column differences are reduced to an average of −0.5 DU when the O3 profile is integrated to 10 hPa with subsequent addition of the O3 climatology above 10 hPa. The RS92 radiosondes are superior in performance compared to other radiosondes, with average 26 km errors of −0.12 hPa or +0.61% O3MR error. iMet-P radiosondes had average 26 km errors of −1.95 hPa or +8.75 % O3MR error. Based on our analysis, we suggest that ozonesondes always be coupled with a GPS-enabled radiosonde and that pressure-dependent variables, such as O3MR, be recalculated/reprocessed using the GPS-measured altitude, especially when 26 km pressure offsets exceed ±1.0 hPa/±5%.

Validation of operational ozone profiles from the Ozone Monitoring Instrument

[1] In this paper we present the validation results of the operational vertical ozone profiles retrieved from the nadir observations by the Ozone Monitoring Instrument (OMI) aboard the NASA Earth Observing System (EOS) Aura platform. The operational ozone profile retrieval algorithm was developed at the Royal Netherlands Meteorological Institute and the OMI mission data has been processed and made publicly available. Advantages of these nadir sounded ozone profiles are the excellent spatial resolution at nadir and daily global coverage while the vertical resolution is limited to 6–7 km. Comparisons with well-validated ozone profile recordings by the Microwave Limb Sounder (MLS) and the Tropospheric Emission Spectrometer (TES), both aboard the NASA EOS-Aura platform, provide an excellent opportunity for validation because of the large amount of collocations with OMI due to the instruments significant geographical overlap. In addition, comparisons with collocated ozone profiles from the Stratospheric Aerosol and Gas Experiment (SAGE-II), the Halogen Occultation Experiment (HALOE), the Global Ozone Monitoring by the Occultation of Stars (GOMOS) and the Optical Spectrograph and Infrared Imager System (OSIRIS) satellite instruments and balloon-borne electrochemical concentration cell (ECC) ozonesondes are presented. OMI stratospheric ozone profiles are found to agree within 20% with global correlative data except for both the polar regions during local spring. For ozone in the troposphere OMI shows a systematic positive bias versus the correlative data sets of order 60% in the tropics and 30% at midlatitude regions. The largest source of error in the tropospheric ozone profile is the fit to spectral stray light in the operational algorithm.

Detailed structure of the tropical upper troposphere and lower stratosphere as revealed by balloon sonde observations of water vapor, ozone, temperature, and winds during the NASA TCSP and TC4 campaigns

We report on balloon sonde measurements of water vapor and ozone using the cryogenic frost point hygrometer and electrochemical concentration cell ozonesondes made at Alajuela, Costa Rica (10.0°N, 84.2°W) during two NASA airborne campaigns: the Tropical Convective Systems and Processes (TCSP) mission in July 2005 and the Tropical Composition, Clouds, and Climate Coupling Experiment (TC4), July–August 2007. In both campaigns we found an upper troposphere that was frequently supersaturated but no evidence that deep convection had reached the tropopause. The balloon sondes were complemented by campaigns of 4 times daily high‐resolution radiosondes from mid‐June through mid‐August in both years. The radiosonde data reveal vertically propagating equatorial waves that caused a large increase in the variability of temperature in the tropical tropopause layer (TTL). These waves episodically produced cold point tropopauses (CPTs) above 18 km, yet in neither campaign was saturation observed above ∼380 K or 17 km. The averages of the water vapor minima below this level were 5.2 ppmv in TCSP and 4.8 ppmv in TC4, and the individual profile minima all lay at or above ∼360 K. The average minima in this 360–380 K layer provide a better estimate of the effective stratospheric entry value than the average mixing ratio at the CPT. We refer to this upper portion of the TTL as the tropopause saturation layer and consider it to be the locus of the final dehydration of nascent stratospheric air. As such, it is the local equivalent to the tape head of the water vapor tape recorder.

In‐flight comparison of Brewer‐Mast and electrochemical concentration cell ozonesondes

The analysis of 140 dual flights between two types of ozonesondes, namely, the Brewer‐Mast (BM) and the electrochemical concentration cell (ECC), is presented in this study. These dual flights were performed before the transition from BM to ECC as the operational ozonesonde for the Payerne Aerological Station, Switzerland. The different factors of the ozonesonde data processing are considered and their influences on the profile of the difference are evaluated. The analysis of the ozone difference between the BM and the ECC ozonesonde data shows good agreement between the two sonde types. The profile of the ozone difference is limited to ±5% (±0.3 mPa) from the ground to 32 km. The analysis confirms the appropriateness of the standard BM data processing method and the usefulness of the normalization of the ozonesonde data. The conclusions of the extended dual flight campaigns are corroborated by the analysis of the time series of the Payerne soundings for the periods of 5 years before and after the change from BM to ECC which occurred in September 2002. No significant discontinuity can be identified in 2002 attributable to the change of sonde.

Atmospheric comparison of electrochemical cell ozonesondes from different manufacturers, and with different cathode solution strengths: The Balloon Experiment on Standards for Ozonesondes

A balloon flight to compare 18 ozonesondes with an ozone photometer and with ozone column measurements from Dobson and Brewer spectrophotometers was completed in April 2004. The core experiment consisted of 12 electrochemical concentration cell ozonesondes, 6 from Science Pump Corporation (SP) and 6 from ENSCI Corporation (ES), prepared with cathode solution concentrations of 0.5% KI (half buffer) and 1.0% KI (full buffer). Auxiliary ozonesondes consisted of two electrochemical concentration cell sondes with 2.0% KI (no buffer), two reconditioned sondes, and two Japanese‐KC96 sondes. Precision of each group of similarly prepared ozonesondes was <2–3%. The six ozonesondes prepared according to the manufacturer's recommendations (SP, 1.0% KI, ES 0.5% KI) overestimated the photometer measurements by 5–10% in the stratosphere, but provided ozone columns in good agreement with the ground‐based spectrophotometer measurements. This is consistent with the difference (∼5%) in ozone photometer and column measurements observed during the experiment. Using cathode cell concentrations of 1.0% KI for ES sondes caused overestimates of the photometer by 10–15% and of ozone column by 5–10%. In contrast, 0.5% KI in SP sondes led to good agreement with the photometer, but underestimates of ozone column. The KC96 sondes underestimated the photometer measurements by about 5–15% at air pressures above 30 hPa. Agreement was within 5% at lower pressures. Diluting the solution concentration and the buffers from 1.0% to 0.5% KI causes an approximately linear pressure‐dependent decrease in ozone for both SP and ES sondes, ratio (0.5 KI/1.0 KI) = 0.9 + 0.024 * log10(Pressure).

Assessment of the performance of ECC‐ozonesondes under quasi‐flight conditions in the environmental simulation chamber: Insights from the Juelich Ozone Sonde Intercomparison Experiment (JOSIE)

Since 1996, quality assurance experiments of electrochemical concentration cell (ECC) ozonesondes of two different model types (SPC‐6A and ENSCI‐Z) have been conducted in the environmental simulation facility at the Research Centre Juelich within the framework of the Juelich Ozone Sonde Intercomparison Experiment (JOSIE). The experiments have shown that the performance characteristics of the two ECC‐sonde types can be significantly different, even when operated under the same conditions. Particularly above 20 km the ENSCI‐Z sonde tends to measure 5–10% more ozone than the SPC‐6A sonde. Below 20 km the differences are 5% or less, but appear to show some differences with year of manufacture. There is a significant difference in the ozone readings when sondes of the same type are operated with different cathode sensing solutions. Testing the most commonly used sensing solutions showed that for each ECC‐manufacturer type the use of 1.0% KI and full buffer gives 5% larger ozone values compared with the use of 0.5% KI and half buffer, and as much as 10% larger values compared with 2.0% KI and no buffer. For ozone sounding stations performing long term measurements this means that changing the sensing solution type or ECC‐sonde type can easily introduce a change of ±5% or more in their records, affecting determination of ozone trends. Standardization of operating procedures for ECC‐sondes yields a precision better than ±(3–5)% and an accuracy of about ±(5–10)% up to 30 km altitude.

Evaluation of ozone measurements from a tethered balloon-sampling platform at South Pole Station in December 2003

Vertical boundary-layer ozone profiles were measured from a tethered balloon platform during the 2003 Antarctic Tropospheric Chemistry Investigation (ANTCI) at South Pole Station, Antarctica. Electrochemical concentration cell (ECC) ozonesondes were used in obtaining 128 ascent and descent profile measurements to about 500 m height during 13–30 December 2003. Various data checks and intercomparisons were done to confirm the accuracy of the ozonesondes. The ozonesondes compared well to a surface ozone ultra-violet (UV) absorption monitor located next to the tether balloon site. During the 18-day period, ozonesonde measurement checks at the surface averaged 0.2±1.0 ppbv higher than the continuous ozone measurements under ambient concentrations ranging from 18 to 51 ppbv. This agreement was also consistent when compared to the nearby NOAA UV-monitor sampling at 17 m above ground level during well-mixed conditions near the surface. In addition to the single ECC sonde profiles, five dual ECC ozonesondes were run on the tether platform. Four release balloon-borne ozonesondes were also launched during the project. Under very sharp ozone gradient events, the release ozonesonde (with a rise rate of ∼4–6 m s −1) passed through the gradient layer too quickly to capture the detail as measured by the controlled tethersonde at ∼0.3 m s −1 ascent/descent rate. Another method of ozone profiling was also done utilizing the UV monitor at the tether site and a 135-m-long Teflon sampling line with a sampling inlet mounted to and raised with the tethered balloon. The ECC ozonesonde averaged about 0.7±0.8 ppbv lower than the long-line sampling method from eight profiles.

Southern Hemisphere Additional Ozonesondes (SHADOZ) 1998–2004 tropical ozone climatology: 3. Instrumentation, station‐to‐station variability, and evaluation with simulated flight profiles

The Southern Hemisphere Additional Ozonesondes (SHADOZ) project has collected more than 3000 ozone profiles from 14 tropical and subtropical sites using balloon‐borne electrochemical concentration cell (ECC) ozonesondes flown with standard radiosondes. Published analysis of ozonesonde precision from SHADOZ profiles measured in 1998–2000 revealed that variations in ozonesonde technique might cause small station‐to‐station biases in the total ozone measurement. We present further evaluation of imprecisions and accuracy based on 1998–2004 SHADOZ data, results from laboratory simulations of ozonesonde flights, and a revised back‐scattered ultraviolet algorithm, the TOMS version 8, 2004 release. The laboratory studies used standard ECC ozonesondes in a flight simulation chamber to evaluate techniques used at SHADOZ stations. Ozone deviations from a standard ozone instrument in the chamber tests resemble those of SHADOZ station data relative to a SHADOZ‐defined climatological reference. Certain systematic variations in SHADOZ ozone profiles are accounted for by differences in solution composition, data processing, and instrument manufacturer. When SHADOZ total ozone column amounts are compared to the new TOMS algorithm, discrepancies between sonde and satellite decline 1–2 percentage points on average, compared to version 7 TOMS.

An analysis on abnormally low ozone in the upper troposphere over subtropical East Asia in spring 2004

Abnormally low ozone (O 3) mixing ratios were observed by electrochemical concentration cell (ECC) ozonesondes in the upper troposphere over subtropical East Asia in spring 2004, a season when high tropospheric O 3 is usually observed in the region. Low O 3 with a lowest mixing ratio of 13 ppbv, less than a fourth of the respective seasonal average of 60–100 ppbv, was observed at 11–18 km above ground over Hong Kong (22.31°N, 114.17°E), Sanya (18.23°N, 109.52°E) and Taipei (24.98°N, 121.43°E). The origin of the low O 3 was investigated using meteorological evidence, satellite imagery and three-dimensional backward air trajectory. We found for the first time that the low O 3 resulted from deep convective pumping of low O 3 maritime air masses near the center of typhoon Sudal from the boundary layer of the tropical region to the east of the Philippines to the upper troposphere. The low O 3 air masses were then transported to the higher latitudes far ahead of the typhoon following the long-range transport driven by the circulations associated with the typhoon and the northern Hadley cell. The findings of this study highlight that more research efforts are needed to understand the effect of the circulation associated with tropical cyclones on the distribution and budget of O 3 and other trace gases in the troposphere.

Validation of ILAS‐II version 1.4 O3, HNO3, and temperature data through comparison with ozonesonde, ground‐based FTS, and lidar measurements in Alaska

Version 1.4 data from the Improved Limb Atmospheric Spectrometer‐II (ILAS‐II) were validated through comparison with profile data measured by several instruments at Poker Flat (65.1°N, 147.5°W), Alaska. The height profiles of O3 and HNO3 provided by ILAS‐II were compared with those retrieved from spectra measured by a ground‐based Fourier transform infrared spectrometer (FTS). The O3 and HNO3 abundances measured by ILAS‐II and FTS in the 17–35 km altitude range agreed within the precision of the two measurements. The O3 volume mixing ratios measured by ILAS‐II above (below) 20 km were 10% lower (higher) than those from the FTS measurements. The HNO3 values from ILAS‐II and FTS agreed to within 10% above 17 km. The O3 profiles obtained from electrochemical concentration cell (ECC) ozonesondes launched from Fairbanks (64.8°N, 147.9°W) were also compared to ILAS‐II data. The ILAS‐II ozone abundance agreed with the ozonesonde values. Comparison of mesospheric and upper stratospheric temperature data obtained by ILAS‐II and Rayleigh lidar indicated that the temperature derived from ILAS‐II was significantly higher (lower) than that from lidar at about 60 (40) km.

An Estimate of the Vertical Ozone Profile Discrepancy between the Australian Brewer–Mast and Electrochemical Concentration Cell Ozonesondes

Abstract An analysis is described that provides an additive correction for referencing the vertical ozone profiles of the Australian Brewer–Mast (BM; October 1984–December 1990) ozonesonde to those of the electrochemical concentration cell (ECC; January 1991–December 1999) using approximately coincident Stratospheric Aerosol and Gas Experiment (SAGE) II satellite ozone profile data. Because Australian BM ozonesondes may have been prepared differently from BM ozonesondes elsewhere, other results of intercomparisons between the two different ozonesonde types cannot be used. However, the present results are consistent with previously reported intercomparison studies between these two ozonesonde types, where the lowest altitude tropospheric ozone levels measured by the BM ozonesonde were approximately 25% lower than the values measured by the ECC ozonesonde. The magnitudes of the BM corrections were found to be generally less than about 0.5 mPa in partial pressure up to an altitude of approximately 28 km. Without direct intercomparison measurements, the corrections given here provide the only means of removing the discontinuity in the Melbourne ozonesonde dataset that occurred when ECC ozonesondes replaced the BM ozonesondes in 1991.

Characteristics of vertical ozone distribution in the lower troposphere in the Yangtze River Delta at Lin’an in the spring of 2001

We analyzed vertical distributions of ozone (O3) in the lower troposphere (< 5 km above ground) at Lin’an (119.75°E, 30.30°N), Zhejiang Province using electrochemical concentration cell (ECC) ozonesonde data obtained from February 21 to April 13, 2001. The results showed that the vertical O3 distributions are controlled by metrological conditions and the characteristics of O3 profiles are related to those of wet bulb potential temperature and wind field. O3 below 2 km showed that the strongest variability and enhanced O3 mixing ratios were associated with easterly winds that blow pollutants from the upwind source region of the Yangtze River Delta (YRD) region. Vertical O3 profiles below 5 km can be grouped into 5 categories: (1) peak mixing ratio type, (2) well-mixed type, (3) layered-structure type, (4) episodic pollution type and (5) altitudinal increasing type. Vertical distributions of O3 affected by regional transport of polluted air masses were investigated. Transport of polluted air from high latitudes of northern China, accompanying subsiding motion of air and stagnant atmospheric conditions are important factors that lead to high mixing ratios of O3 at Lin’an. The stagnant atmospheric conditions associated with a continental high pressure system and pollution plume transported from the YRD and central-eastern China also lead to regional accumulation of O3 and high O3 mixing ratio at Lin’an. Long-range transport of O3 and pollutants from the Pearl River Delta in South China and insitu O3 formation also resulted in elevated O3 mixing ratios at around 1 km altitudes and layered O3 distribution in the lower troposphere.

Influence of Biomass Burning in Southeast Asia on the Lower Tropospheric Ozone Distribution Over South China

AbstractOzone enhancement was observed in the lower troposphere over Hong Kong and Kunming on 7 and 8 March 2001 using the electrochemical concentration cell ozonesondes. Based on the data of NCEP, total column ozone, numerical simulation of MM5, AI from TOMS, aerosol optical depths from MODIS, and CO concentration from MOPITT, the influence of biomass burning in Southeast Asia on the ozone distribution in the lower troposphere over Hong Kong and Kunming is analyzed. The transport of the emissions of biomass burning shows that the enhancement of the lower tropospheric ozone over Hong Kong and Kunming is from the region where large‐scale fires occurred in Southeast Asia. TOMS AI images and the atmospheric background circulations reveal that the biomass burning plumes in Southeast Asia can be transported to downwind South/Southwest China and lead to enhancement of the ozone concentration in the lower troposphere.

A meteorological analysis on a low tropospheric ozone event over Xining, North Western China on 26–27 July 1996

A pronounced low tropospheric ozone (O3) event was observed over the Tibetan plateau in Xining (XN) (101.45°E, 36.43°N, 2296 m a.s.l), Northwestern China by electrochemical concentration cell ozonesonde from 25–27 July 1996. The event featured very low O3 mixing ratio (<56 ppbv) below 15 km above ground and high relative humidity (30–100%). A comparison with the vertical distribution of tropospheric O3 over Lhasa (91.03°E, 29.40°N, 3650 m a.s.l) has suggested that the low tropospheric O3 mixing ratio over XN represented a common characteristic of tropospheric O3 over the Tibetan plateau. Meteorological measurements from the regional radiosonde network in China and satellites revealed that the low O3 event was associated with an anticyclone in the upper troposphere, which was characterized by an intensive upwelling transport. The dynamical processes of the transport were investigated using latitudinal cross-section analysis on the National Centre of Environmental Prediction data set and three-dimensional backward trajectories. The results showed that the O3-depleted air originated from Southeast Asia or the marine boundary layer of the South China Sea and had travelled across the Tibetan plateau where an ‘O3 valley’ was observed at the time during the long-range transport inland over XN.

Origin of the springtime tropospheric ozone maximum over east China at LinAn in 2001

Tropospheric ozone (O 3 ) profiles over the east China coast at LinAn (30.30°N, 119.75°E) were measured by electrochemical concentration cell ozonesondes in the spring of 2001. The measurement revealed that extremely high O 3 with mixing ratios up to 1200 ppbv sometimes penetrated deeply into 8.5–16 km above sea level as a result of lowering of the tropopause across the East Asia strong subtropical jet stream. In addition, high O 3 in the 75–150 ppbv range penetrated into the upper and middle troposphere following the extreme O 3 regimes and caused an overall high O 3 mixing ratio in these regions. The occurrence of the high O 3 regimes followed the propagation of dry air with low relative humidity and high potential vorticity suggesting that the O 3 is of stratospheric origin. High O 3 episodes with O 3 mixing ratios in the 75–100 ppbv range were observed in the lower troposphere and especially in the boundary layer. Trajectory analysis suggested that the O 3 -rich air masses had passed through the industrialized and urbanized zones of the Pearl River Delta region of south China, northeast China coast and Yangtze River Delta region of east China. The O 3 is probably of anthropogenic origin resulting from photochemical formation from pollutants emitted from these regions. Our analysis thus revealed that over the east China coast at LinAn, stratospheric O 3 is still the predominant source of O 3 in the middle and upper troposphere, while anthropogenic sources caused a high O 3 pollution episode in the boundary layer. DOI: 10.1034/j.1600-0889.2003.00079.x

Estimation of Arctic polar vortex ozone loss during the winter of 1999–2000 using vortex‐averaged airborne differential absorption lidar ozone measurements referenced to N2O isopleths

The NASA Langley UV differential absorption lidar (DIAL) system flew on the NASA DC‐8 aircraft during the Stratospheric Aerosol and Gas Experiment (SAGE) III Ozone Loss and Validation Experiment/Third European Stratospheric Experiment on Ozone 2000 (SOLVE/THESEO 2000) mission from 30 November 1999 to 15 March 2000. The UV DIAL system measured ozone (O3) profiles at altitudes from about 1 km above the aircraft up to about 26 km with a vertical resolution of 750 m and a horizontal resolution of 70 km below 19 km and 140 km above 19 km. In comparison with electrochemical concentration cell ozonesonde profiles, the UV DIAL O3 measurements agreed to within 5% up to 20 km and 10% from 20 to 25 km. Ozone loss during the season was determined using the UV DIAL O3 data along with air mass subsidence determined using N2O as a conservative tracer at five levels from 50 to 250 ppbv [Greenblatt et al., 2002]. O3 mixing ratios were determined inside the polar vortex, away from the collar region along these five levels during the mission. The maximum O3 loss determined from 30 November to 12 March was 1.55 ± 0.3 ppmv at the 440–450 K potential temperature (Θ) level, while the loss there between 20 January and 15 March was 1.3 ± 0.3 ppmv. These results are comparable to many of the other reported losses for these periods, but lower than several. Some of the determinations of higher losses used a different method to determine descent during the season. These results indicate that a series of vertical profiles of O3 that sample much of the vortex during the winter, along with determinations of the descent of air masses inside the vortex, can give a reasonable estimate of the O3 changes during the season.

Southern Hemisphere Additional Ozonesondes (SHADOZ) 1998–2000 tropical ozone climatology 1. Comparison with Total Ozone Mapping Spectrometer (TOMS) and ground‐based measurements

A network of 10 southern hemisphere tropical and subtropical stations, designated the Southern Hemisphere Additional Ozonesondes (SHADOZ) project and established from operational sites, provided over 1000 ozone profiles during the period 1998–2000. Balloon‐borne electrochemical concentration cell (ECC) ozonesondes, combined with standard radiosondes for pressure, temperature, and relative humidity measurements, collected profiles in the troposphere and lower to midstratosphere at: Ascension Island; Nairobi, Kenya; Irene, South Africa; Réunion Island; Watukosek, Java; Fiji; Tahiti; American Samoa; San Cristóbal, Galapagos; and Natal, Brazil. The archived data are available at: 〈http://croc.gsfc.nasa.gov/shadoz〉.1 In this paper, uncertainties and accuracies within the SHADOZ ozone data set are evaluated by analyzing: (1) imprecisions in profiles and in methods of extrapolating ozone above balloon burst; (2) comparisons of column‐integrated total ozone from sondes with total ozone from the Earth‐Probe/Total Ozone Mapping Spectrometer (TOMS) satellite and ground‐based instruments; and (3) possible biases from station to station due to variations in ozonesonde characteristics. The key results are the following: (1) Ozonesonde precision is 5%. (2) Integrated total ozone column amounts from the sondes are usually to within 5% of independent measurements from ground‐based instruments at five SHADOZ sites and overpass measurements from the TOMS satellite (version 7 data). (3) Systematic variations in TOMS‐sonde offsets and in ground‐based‐sonde offsets from station to station reflect biases in sonde technique as well as in satellite retrieval. Discrepancies are present in both stratospheric and tropospheric ozone. (4) There is evidence for a zonal wave‐one pattern in total and tropospheric ozone, but not in stratospheric ozone.

Stratospheric Ozone Loss over Eureka in 1999/2000 Observed with ECC Ozonesondes

In 1999/2000, as many as 51 Electrochemical Concentration Cell (ECC) ozonesondes were launched from December to March at the Canadian Arctic Eureka observatory (80°N, 86°W), one of the most northern stations in the Arctic, and the temporal evolution of the vertical ozone profiles was obtained in detail. During the winter, monthly average total ozone and temperature at 50 hPa, both observed with the ECC ozonesondes, were substantially lower than normal over Eureka since 1993. From December to March, Eureka was most of the time inside the polar vortex in the lower stratosphere (475 K isentropic surface level), except for early March. When Eureka was inside the polar vortex, very low temperatures were observed in the lower stratosphere, in accordance with the detection of Polar Stratospheric Clouds (PSCs) by Mie lidar between the 17 and 22 km level in January. However, PSCs were not observed over Eureka around the same altitude in February. Together with the observations of large HNO3-containing particles by the ER-2, and depleted HNO3 by the UARS Microwave Limb Sounder, the lidar observations suggest the denitrification in the lower stratosphere in late winter inside the vortex. Under these conditions, the intravortex ozone mixing ratio on the 475 K isentrope decreased by about 2.2 ppmv from 3.1 ppmv on the 497 K isentrope (4 February), to 0.9 ppmv on the 475 K isentrope (29 March) in late winter to early spring, following the diabatic descent. In this period, the loss rate inside the vortex was found to be 0.041±0.008 ppmv/day (90% confidence interval). These findings and results are consistent with other observations (THESEO 2000/SOLVE campaign), and suggest that significant chemical ozone loss did occur in the lower stratosphere inside the polar vortex during the winter of 1999/2000.

Origin of the springtime tropospheric ozone maximum over east China at LinAn in 2001

Tropospheric ozone (O3) profiles over the east China coast at LinAn (30.30°N, 119.75°E) were measured by electrochemical concentration cell ozonesondes in the spring of 2001. The measurement revealed that extremely high O3 with mixing ratios up to 1200 ppbv sometimes penetrated deeply into 8.5–16 km above sea level as a result of lowering of the tropopause across the East Asia strong subtropical jet stream. In addition, high O3 in the 75–150 ppbv range penetrated into the upper and middle troposphere following the extreme O3 regimes and caused an overall high O3 mixing ratio in these regions. The occurrence of the high O3 regimes followed the propagation of dry air with low relative humidity and high potential vorticity suggesting that the O3 is of stratospheric origin. High O3 episodes with O3 mixing ratios in the 75–100 ppbv range were observed in the lower troposphere and especially in the boundary layer. Trajectory analysis suggested that the O3-rich air masses had passed through the industrialized and urbanized zones of the Pearl River Delta region of south China, northeast China coast and Yangtze River Delta region of east China. The O3 is probably of anthropogenic origin resulting from photochemical formation from pollutants emitted from these regions. Our analysis thus revealed that over the east China coast at LinAn, stratospheric O3 is still the predominant source of O3 in the middle and upper troposphere, while anthropogenic sources caused a high O3 pollution episode in the boundary layer.