Abstract. An airfreight container with automated

Measurements from the winter of 1994-95 indicating removal of total reactive nitrogen from the Arctic stratosphere by particle sedimentation were used to constrain a microphysical model. The model suggests that denitrification is caused predominantly by nitric acid trihydrate particles in small number densities. The denitrification is shown to increase Arctic ozone loss substantially. Sensitivity studies indicate that the Arctic stratosphere is currently at a threshold of denitrification. This implies that future stratospheric cooling, induced by an increase in the anthropogenic carbon dioxide burden, is likely to enhance denitrification and to delay until late in the next century the return of Arctic stratospheric ozone to preindustrial values.

Abstract. A large airfreight container with automated instruments for measurement of atmospheric gases and trace compounds was operated on a monthly basis onboard a Boeing 767-300 ER of LTU International Airways during long-distance flights from 1997 to 2002 (CARIBIC, Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container, http://www.caribic-atmospheric.com). Subsequently a more advanced system has been developed, using a larger capacity container with additional equipment and an improved inlet system. CARIBIC phase #2 was implemented on a new long-range aircraft type Airbus A340-600 of the Lufthansa German Airlines (Star Alliance) in December 2004, creating a powerful flying observatory. The instrument package comprises detectors for the measurement of O3, total and gaseous H2O, NO and NOy, CO, CO2, O2, Hg, and number concentrations of sub-micrometer particles (>4 nm, >12 nm, and >18 nm diameter). Furthermore, an optical particle counter and a proton transfer mass spectrometer (PTR-MS) are installed. Aerosol samples are collected for analyses of elemental composition and particle morphology after flight. Air samples are taken in glass containers for laboratory analyses of hydrocarbons, halocarbons and greenhouse gases in several laboratories. Absorption tubes collect oxygenated volatile organic compounds. Three differential optical absorption spectrometers (DOAS) with their telescopes mounted in the inlet system measure atmospheric trace gases such as BrO, HONO, and NO2. A video camera mounted in the inlet provides information about clouds along the flight track. Here we describe the flying observatory and report examples of measurement results.

Abstract. In the troposphere, anthropogenic emissions of nitrogen oxides, hydrocarbons and carbon monoxide cause large-scale photochemical build up of ozone. In the stratosphere breakdown of anthropogenic halocarbons damages the ozone layer. In the extratropics a transition region between these air layers occurs, the lowermost stratosphere (below 12-14 km), in which about half the current subsonic air traffic takes place. Here, we report aircraft measurements of HNO3, 03 and CO over western Europe in July 1994 (5 flights of several hours during a 10-day period), at approximately 1-2 km above the tropopause. The HNO3 mixing ratios observed were highly variable (0.76-1.2 ppbv), while HNO3/O3 ratios seem relatively high (5.2-7.0-10'3). Moreover, several times we observed very high levels of pollutant CO (up to -•0.5 ppmv) that did not originate from aircraft exhausts. Instead, we pose that it had mixed-in from the troposphere. Cross-tropopause mixing also helps explaining the variable HNO3 and relatively high HNO3/O3 ratios. These measurements suggest that relatively short-lived surface emitted pollutants can reach the lowermost stratosphere. We expect that this contributes to 03 formation.

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