[1] 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 * log 10 (Pressure).

Daily ozone soundings taken from the R/V Ronald H. Brown from 7 July through 11 August 2004 as part of the Intercontinental Chemical Transport Experiment (INTEX) Ozonesonde Network Study (IONS) are used to investigate the vertical structure of ozone over the Gulf of Maine and to characterize variability in sources of tropospheric ozone: stratosphere, regional convection and lightning, advection, and local boundary layer pollution. These soundings were part of a network of twelve IONS (http://croc.gsfc.nasa.gov/intex/ions.html) stations that launched ozonesonde‐radiosonde packages over the United States and maritime Canada during the INTEX/International Consortium for Atmospheric Research on Transport and Transformation (ICARTT)/New England Air Quality Study (NEAQS) project from 1 July to 15 August 2004. Four of the IONS stations were in mid‐Atlantic and northeast United States; four were in southeastern Canada. Although the INTEX/ICARTT goal was to examine pollution influences under stable high‐pressure systems, northeastern North America (NENA) during IONS was dominated by weak frontal systems that mixed aged pollution and stratospheric ozone with ozone from more recent pollution and lightning. These sources are quantified to give tropospheric ozone budgets for individual soundings that are consistent with tracers and meteorological analyses. On average, for NENA stations in July‐August 2004, tropospheric ozone was composed of the following: 10–15% each local boundary layer and regional sources (the latter including that due to lightning‐derived NO) and 20–25% stratospheric ozone, with the balance (∼50%) a mixture of recently advected ozone and aged air of indeterminate origin.

The ozonesonde is a small balloon-borne instrument that is attached to a standard radiosonde to measure profiles of ozone from the surface to 35 km with ∼100-m vertical resolution. Ozonesonde data constitute a mainstay of satellite calibration and are used for climatologies and analysis of trends, especially in the lower stratosphere where satellites are most uncertain. The electrochemical concentration cell (ECC) ozonesonde has been deployed at ∼100 stations worldwide since the 1960s, with changes over time in manufacture and procedures, including details of the cell chemical solution and data processing. As a consequence, there are biases among different stations and discontinuities in profile time series from individual site records. For 22 years the Jülich (Germany) Ozonesonde Intercomparison Experiment (JOSIE) has periodically tested ozonesondes in a simulation chamber designated the World Calibration Centre for Ozonesondes (WCCOS) by WMO. During October–November 2017 a JOSIE campaign evaluated the sondes and procedures used in Southern Hemisphere Additional Ozonesondes (SHADOZ), a 14-station sonde network operating in the tropics and subtropics. A distinctive feature of the 2017 JOSIE was that the tests were conducted by operators from eight SHADOZ stations. Experimental protocols for the SHADOZ sonde configurations, which represent most of those in use today, are described, along with preliminary results. SHADOZ stations that follow WMO-recommended protocols record total ozone within 3% of the JOSIE reference instrument. These results and prior JOSIEs demonstrate that regular testing is essential to maintain best practices in ozonesonde operations and to ensure high-quality data for the satellite and ozone assessment communities.