The Indian Ocean Experiment (INDOEX) was an international, multiplatform field campaign to measure long-range transport of air pollution from South and Southeast Asia toward the Indian Ocean during the dry monsoon season in January to March 1999. Surprisingly high pollution levels were observed over the entire northern Indian Ocean toward the Intertropical Convergence Zone at about 6 degrees S. We show that agricultural burning and especially biofuel use enhance carbon monoxide concentrations. Fossil fuel combustion and biomass burning cause a high aerosol loading. The growing pollution in this region gives rise to extensive air quality degradation with local, regional, and global implications, including a reduction of the oxidizing power of the atmosphere.

Abstract. Tentative estimates, using three-dimensional chemistry and transport models, have suggested small ozone increases in the upper troposphere resulting from current aircraft emissions, but have also concluded to significant deficiencies in today's models and to the need to improve them through comparison with extended data sets. The Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC) program was initiated in 1993 by European scientists, aircraft manufacturers, and airlines to collect experimental data. Its goal is to help understand the atmosphere and how it is changing under the influence of human activity, with particular interest in the effects of aircraft. MOZAIC consists of automatic and regular measurements of ozone and water vapor by five long range passenger airliners flying all over the world. The aim is not to detect direct effects of aircraft emissions on the ozone budget inside the air traffic corridors but to build a large database of measurements to allow studies of chemical and physical processes in the atmosphere, and hence to validate global chemistry transport models. MOZAIC data provide, in particular, detailed ozone and water vapor climatologies at 9-12 km where subsonic aircraft emit most of their exhaust and which is a very critical domain (e.g., radiatively and stratosphere/troposphere exchanges) still imperfectly described in existing models. This will be valuable to improve knowledge about the processes occuring in the upper troposphere and the lowermost stratosphere, and the model treatment of near tropopause chemistry and transport. During MOZAIC I (January 1993-September 1996), fully automatic devices were developed,

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Abstract. Ten data sets coveting the period 1954-2000 are analyzed to show a 1%/yr increase in stratospheric water vapor. The trend has persister for at least 45 years, hence is unl•ely the result of a single event, but rather indicative of long-term climate change. A long-term change in the transport ofwater vapor into the stratosphere is the most probable cause.

Abstract. The fast-response resonance fluorescence instrument for the airborne measurement of carbon monoxide described by Gerbig et al. [1996] was modified by implementing an improved optical filter with more efficient optics and an optimized resonance lamp. Besides reductions in size and weight, the new instrument achieves a sensitivity 10 times higher, a lower background (65 ppb compared with 250 ppb), and a faster time response (<0.1s) than the original instrument. The precision is _+ 1.5 ppb at an atmospheric mixing ratio of 100 ppb CO, and the detection limit is 3 ppb (20-) for an integration time of 1 s. First results from the North Atlantic Regional Aerosol Characterization Experiment (ACE-2) campaign during July 1997, when the new instrument was deployed aboard the U.K. Meteorological Office C-130 aircraft, are used to demonstrate the performance of the new instrument. . These authors concluded on the basis of laboratory experiments and theoretical considerations that a large fraction of the observed background signal, which determines the achievable precision and detection limit, was not due to stray light, e.g. from the walls of the fluorescence chamber, but originated from continuum resonance Raman scattering by oxygen molecules. This finding put a new light on the required reduction of stray light as originally proposed by Volz and Kley [1985] and opened the door for a redesign of the instrument in order to improve its performance. A further reason for the redesign was to make the technique available to a wider scientific community, which was realized in the framework of a technology transfer contract. In this paper the new instrument is described, and a few examples of measurements over the Atlantic during ACE2 are shown to illustrate its performance. The New InstrumentThe new instrument is shown schematically in Figure 1. It consists of the same principal components as the old instrument, namely, a resonance lamp excited by a RF discharge, an optical filter for selection of the appropriate wavelength interval around 150 nm, which images the lamp into the RF chamber, where the fluorescence is viewed at a right angle by means of a photomultiplier tube (PMT) with suprasil optics. The 1699

A series of measurements over the equatorial Pacific in March 1993 showed that the volume mixing ratios of ozone were frequently well below 10 nanomoles per mole both in the marine boundary layer (MBL) and between 10 kilometers and the tropopause. These latter unexpected results emphasize the enormous variability of tropical tropospheric ozone and hydroxyl concentrations, which determine the oxidizing efficiency of the troposphere. They also imply a convective short circuit of marine gaseous emissions, such as dimethyl sulfide, between the MBL and the uppermost troposphere, leading, for instance, to sulfate particle formation.

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Gas‐phase isotopic exchange between NO and NO2 enriches the heavier 15N isotope in the more oxidized form. In the atmosphere the concentration of both gases, NO and NO2, is controlled during daytime by the Leighton relationship through the oxidation of NO with O3 and the photolytic reaction of NO2 to NO. For atmospheric concentrations (e.g., NOx, ∼10 ppb), isotopic exchange and photolytic reaction are very fast with characteristic time constants of a few minutes compared to other removing reactions of atmospheric NOx via OH radicals (daytime reaction) and O3 (nighttime reaction) with time constants of some hours and more. We have found from 15N/14N measurements of atmospheric NO2 and NOx at Jülich that both processes, isotopic exchange and photolytic reaction, interact and have an influence on the 15N/14N isotopic ratio. This interaction, together with seasonal variations of the NOx/O3 ratio at daytime and either complete oxidation of NO to NO2 or isotopic exchange between NO and NO2 at nighttime, explains the seasonal variation of the 15N/14N ratio of atmospheric NO2, which agrees with results from a simple model.