Ozone sonde cell current measurements and implications for observations of near-zero ozone concentrations in the tropical upper troposphere

摘要

Laboratory measurements of the Electrochemical Concentration Cell (ECC)ozone sonde cell current using ozone free air as well as defined amounts ofozone reveal that background current measurements during sonde preparationare neither constant as a function of time, nor constant as a function ofozone concentration. Using a background current, measured at a defined timedafter exposure to high ozone may often overestimate the real background,leading to artificially low ozone concentrations in the upper tropicaltroposphere, and may frequently lead to operator dependent uncertainties.Based on these laboratory measurements an improved cell current to partialpressure conversion is proposed, which removes operator dependentvariability in the background reading and possible artifacts in thismeasurement. Data from the Central Equatorial Pacific Experiment (CEPEX)have been reprocessed using the improved background treatment based on theselaboratory measurements. In the reprocessed data set near-zero ozone eventsno longer occur. At Samoa, Fiji, Tahiti, and San Cristóbal, nearly allnear-zero ozone concentrations occur in soundings with larger backgroundcurrents. To a large extent, these events are no longer observed in thereprocessed data set using the improved background treatment.