The global carbon cycle is so complex and intricate that even a network as dense as the NOAA/CMDL global, cooperative flask network cannot provide sufficient data to resolve all budget complexities. Nevertheless, the network is substantially larger than any other trace gas-monitoring network in the world and is expanding. The extension of the network in recent years to include data-sparse regions, continental sites, and shipboard measurements has been driven by data needs to address specific global carbon-cycle research questions.

Weekly flask sampling is sufficient to identify long-term trends in atmospheric CO₂ mixing ratios and to identify regional and hemispheric atmospheric CO₂ features. However, this weekly sampling regime may not provide sufficient data for some studies, such as those looking at diurnal or hourly variations in the atmospheric CO₂ records. For these studies, individuals may want the NOAA/CMDL continuous CO₂ database from their four in situ monitoring sites (Barrow, Mauna Loa, Samoa, and the South Pole). Like the database described in this numeric data package (NDP), the continuous CO₂ database is available from both CMDL and CDIAC.

Whereas NOAA/CMDL CO₂ flask data have been expressed in several Scripps Institution of Oceanography (SIO) provisional CO₂ calibration scales, the data presented here have been updated to the SIO 1993 manometric mole fraction scale by using SIO calibration values of 15 NOAA/CMDL reference gases with concentrations ranging from 246.6 to 520.7 ppm. Corrections for the temporal drift of the calibration gases used for sample analyses were applied where necessary. Corrections for nonlinearity of the NDIR analyzer have been applied as needed since sampling began in the late 1960s.

Some of the early flasks were not suitable for particular locations or for sampling the full suite of parameters measured by NOAA/CMDL. However, the flasks presently used by NOAA/CMDL are not believed to have the limitations of the earlier flasks and are suitable for monitoring numerous gas species simultaneously.

This database contains some CO₂ measurements that are not considered indicative of background tropospheric conditions. Please pay attention to the flag codes associated with each CO₂ determination. To avoid erroneous analysis and interpretation of these data, users should read and understand all associated readme files before using the data files. Users are strongly advised to consult the relevant published literature. Although NOAA/CMDL has attempted to provide the most accurate and precise measurements possible in a timely manner, this database is subject to change. The NOAA/CMDL Carbon Cycle Group reserves the right to adjust the data in these files on the basis of recalibrations of reference gases and instruments.

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