Focus

The importance of the tropopause region:

Use is made of a passenger aircraft for making frequent atmospheric chemistry measurements mainly in the tropopause region. Relatively few measurements are available for this important region. The tropopause is the division between the troposphere (this is the lower well mixed part of the atmosphere where the weather as we know it takes place) and the stratosphere (this is the not so well mixed, layered part of the atmosphere). In the stratophere temperatures increase with altitude due to the presence of the ozone layer.

First of all, the cross-tropopause transport mechanisms are not yet known in sufficient detail. This makes it for instance difficult to estimate reliably how much ozone is imported from the stratosphere.

Secondly, the chemistry in the tropopause region is not well documented. Pollutants uplifted from the boundary layer, and nitrogen oxides formed by lightning create a complex chemical mix in this region.

At last, but not least, aerosol (very small particles), the role of which presently receives increasing attention because of radiative forcing, and its role in cloud formation, is extremely poorly researched in all aspects like abundance, size distribution, and chemical composition. There is a great deal of uncertainty in the complex 3 dimensional chemistry transport models that are being continuously developed, improved, and refined to reconstruct better the essential aspects of the chemistry of the atmosphere. Difficulties range from incomplete chemistry to fundamental flaws in basic aspects like transport mechanisms. Measurements remain vital for validation (this is nice for experimentalists to know).

Research aircraft flights can provide targeted highly specialized or extensive chemical and physical surveys. Such projects are very expensive, and cannot cover larger parts of the global atmosphere at a desired frequency and affordable cost. Also true is that passenger aircraft based research cannot compete with the extensive complex capacity of research aircraft. But they clearly can help to obtain a vast amount of data as is demonstrated in a convincing way by the project MOZAIC, which entails the collection of ozone and water vapor data using 5 Airbus aircraft (Alain Marenco http://www.aero.obs-mip.fr/mozaic/).

CARIBIC is somewhere between research aircraft and MOZAIC. We deploy several automated analyzers and an air sampler in an air freight container. Another airliner atmospheric chemistry project we are aware of is: JAL (continuing), a Japanese Boeing 747 with an air sampling system.

The great strength of the CARIBIC container concept is that the instrument package is large, flexible and extendable. To some degree CARIBIC is a flying laboratory that analyses the air in great detail.