Consistency evaluation of tropospheric ozone from ozonesonde and IAGOS aircraft observations: vertical distribution, ozonesonde types and station-airport distance

Abstract. The vertical distribution of tropospheric O₃ from ozonesondes is compared with that from In-service Aircraft for a Global Observing System (IAGOS) measurements at 23 pairs of sites between about 30° S and 55° N, from 1995 to 2021. Profiles of tropospheric O₃ from IAGOS aircraft are in generally good agreement with ozonesonde observations, for ECC, Brewer-Mast, and Carbon-Iodine sensors, with average biases of 7.03 ppb, 6.28 ppb, and -4.48 ppb, and correlation coefficients (R) of 0.72, 0.86, and 0.82, respectively. Agreement between the aircraft and Indian-sonde observations is poor, with an average bias of 24.07 ppb and R of 0.41. The O₃ concentration observed by ECC sondes is on average higher by 5–10 % than that observed by IAGOS aircraft, and the relative bias increases modestly with altitude. For other sonde types, there are some seasonal and altitude variations in the relative bias with respect to IAGOS measurements, but these appear to be caused by local differences.

The distance between station and airport within 4° has little effect on the comparison results. For the ECC ozonesonde, the overall bias with respect to IAGOS measurements varies from 5.7 to 9.8 ppb, when the station pairs are grouped by station-airport distances of <1° (latitude and longitude), 1–2°, and 2–4°. Correlations for these groups are R = 0.8, 0.9 and 0.7. These comparison results provide important information for merging ozonesonde and IAGOS measurement datasets. They can also be used to evaluate the relative biases of the different sonde types in the troposphere, using the aircraft as a transfer standard.