Observations of trace gases during CARIBIC flights

The CARIBIC project (Civil Aircraft for the Regular Investigation of the Atmosphere Based on an Instrument Container) involves the monthly deployment of an instrument container equipped to make atmospheric measurements from aboard a long-range commercial airliner. The instrument package housed in the container is fully automated and during each flight carries out a variety of real-time trace gas and aerosol measurements, and also collects air samples in glass sampling flasks, which are analyzed post-flight. Measurements made from the sampling flasks include greenhouse gases, halocarbons and nonmethane hydrocarbons. Real-time measurements include ozone and carbon monoxide.

The first phase of CARIBIC was conducted between 1997 and 2002, with the instrument container aboard a Boeing 767-300ER operated by LTU International Airways. These flights originated in Germany and went primarily to destinations in the Caribbean and the Indian Ocean, with some flights to southern Africa. Since December 2004, flights for the second phase of CARIBIC have been aboard a Lufthansa Airbus A340-600. Flights originate in Frankfurt, Germany with routes to India, East Asia, South America, and North America.

The long-distance routes on which the CARIBIC container is deployed typically encounter air masses that are representative of the free troposphere when in the tropics, and the upper troposphere/lowermost stratosphere (UT/LMS) at mid- to high latitudes. As such, CARIBIC allows for the routine monitoring of these atmospheric regions; monitoring of the UT/LMS is of particular interest, as this one of the less studied, and therefore, less well understood, regions of the atmosphere.

While less frequent than real-time measurements, flask samples allow for the analysis of a much larger suite of trace gases and ultimately provide a more detailed description of the chemical composition of the different atmospheric regions encountered during CARIBIC flights. The compounds measured are also useful for investigations of air mass features such as source regions and age. Presented here is an overview of flask sample trace gas measurements, including spatial and temporal trends in these compounds, with an emphasis on the chemical composition of the UT/LMS region.