On the outward journey, European air masses, loaded by photochemically produced ozone, may have partly influenced the measurements in clean air. As simultaneously measured low concentrations of Krypton-85 (which only has anthropogenic sources) show, the high ozone mixing ratios at 0-5°N cannot be explained by photochemical formation, but must be of natural origin. On the return journey, the ITCZ was at 6°S and was weak. This explains the very low ozone values of only 4 ppb at times, caused by the photolysis of ozone.The ozone device was housed in the crow's nest, to avoid ship-polluted interference. At later cruises, the instrument was placed near the weather station, because the maintenance in the crow’s nest was impractical and the new air intake at the uppermost railing turned out to be suitable as well. As a precaution, the air pump was changed nine times during the trip. At the end of the last section, the pump wobbled a little, resulting in a five percent loss of production, which could be corrected

Positions partly approximate