This obspack compiles observations of atmospheric O2 from several different measurement programs into a single product.
The atmospheric O2 measurement community, unlike the CO2 measurement community, lacks a common scale or Central Calibration Laboratory. 
The user should be aware that the data from these measurement programs have not been "harmonized", i.e. brought onto a common scale 
with multiple layers of quality control. This means that data from different programs are not formally compatible, and should not be 
incorporated into the same analyses. Intercomparisons have shown that the offsets between measurement programs are poorly constrained, 
time-dependent, and often much larger than "real" variability, meaning that without additional information, many spatial or temporal gradients 
between measurement programs cannot be interpreted. The data are instead provided with the expectation that the user will consult
with the measurement providers as to the specifics of their application, and whether it is recommended to directly combine data from multiple programs.