As part of the North American Carbon Program (NACP) Implementation Plan, the vertical profiles of carbon dioxide, carbon monoxide and methane are being measured on a weekly basis at about a dozen aircraft and communication tower (about 500 m height) sites in the United States and Canada in a pilot program designed to reduce the uncertainty in the size of the North American carbon dioxide uptake by terrestrial processes. The goal is to have an observing system of 36 total profiling sites in place by 2007. Modeling exercises suggest that this system would reduce the current uncertainty in the size of the North American carbon dioxide flux (currently on the order of +/-0.6 Pg C per year) by a factor of two. In 2004, additional sites were implemented in the north-central U.S. in support of a major NACP intensive study scheduled for 2005.
The sampling systems include continuous measurements at several heights on the towers and a multi-flask automated sampling system for the aircraft. The latter is designed so that it can be easily installed on any small Cessna-class aircraft and does not require the attention of the pilot. The sampling and control systems are in two separate luggage-sized cases; the sampling case is returned to the laboratory in Boulder after exposure for analysis. This system allows rapid turn-around of samples and, in addition to mixing ratio profiles to altitudes on the order of 8 km, allows for isotopic carbon and oxygen analyses. Sample data from the towers and aircraft will be shown and the current status of inverse model estimates of the North American carbon sink will be discussed.