Budgets of O sub(3) and CO in the upper troposphere: CARIBIC passenger aircraft results 1997-2001

In situ measurements of ozone (O sub(3)) and carbon monoxide (CO) were conducted using a passenger aircraft during 47 flights (November 1997 to April 2001) between Germany and the Indian Ocean region at 10-11 km altitude, project Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container (CARIBIC). Here, emphasis is on a better understanding of the budgets of O sub(3) and CO in the middle and upper northern hemispheric (NH) troposphere. Latitudinal and seasonal variations of the mean values and the local variability of O sub(3) and CO are assessed. CO is moreover applied as tracer of polluted (surface) air, that is, as a measure of O sub(3) precursors. This enables us to assign positive or negative O sub(3)-CO correlations and their slopes alpha = dO sub(3)/dCO to O sub(3) produced by photochemistry or to O sub(3) imported from the stratosphere. In the tropics, photochemical O sub(3) production clearly dominates all year round, with mean O sub(3)-CO slopes of 0.45-0.53 in spring/summer and 0.20-0.27 in autumn/winter. Over the Arabian Sea and the Middle East, high annual net O sub(3) production rates in the troposphere of 17.6 x 10 super(10) O sub(3) molecules cm super(-2) s super(-1) are estimated. In the extratropics, the well-documented springtime O sub(3) maximum emerged in the CARIBIC data set. Stratospheric O sub(3) influx and photochemical O sub(3) production contribute equally to this spring maximum. In summer, photochemical O sub(3) formation clearly dominates, in winter, per contra, stratospheric O sub(3) influx clearly dominates. In the extratropics, CO shows a sine seasonal variation between similar to 81 ppbv in September and similar to 111 ppbv in March, being delayed by similar to 5 weeks compared to ground-based background monitoring stations. In the tropics, however, no significant seasonal variations of CO were observed, mainly because of occasional high CO periods such as those associated with the 1997 Indonesian forest fires or the outflow of the Intertropical Convergence Zone, which pumps in summer immense amounts of pollutants emitted in South Asia (India, Bangladesh, Indochina) to the 10-11 km altitude range surveyed during CARIBIC.