Precise atmospheric oxygen measurements with a paramagnetic oxygen analyzer

A methodology has been developed for making continuous, high‐precision measurements of atmospheric oxygen concentrations by modifying a commercially available paramagnetic oxygen analyzer. Incorporating several design improvements, an effective precision of 0.2 ppm O 2 from repeated measurements over a 1‐hour interval was achieved. This is sufficient to detect background changes in atmospheric O 2 to a level that constrains various aspects of the global carbon cycle. The analyzer was used to measure atmospheric O 2 in a semicontinuous fashion from air sampled from the end of Scripps Pier, La Jolla, California, and data from a 1‐week period in August 1996 are shown. The data exhibit strongly anticorrelated changes in O 2 and CO 2 caused by local or regional combustion of fossil fuels. During periods of steady background CO 2 concentrations, however, we see additional variability in O 2 concentrations, clearly not due to local combustion and presumably due to oceanic sources or sinks of O 2 . This variability suggests that in contrast to CO 2 , higher O 2 sampling rates, such as those provided by continuous measurement programs, may be necessary to define an atmospheric O 2 background and thus aid in validating and interpreting other O 2 data from flask sampling programs. Our results have also demonstrated that this paramagnetic analyzer and gas handling design is well suited for making continuous measurements of atmospheric O 2 and is suitable for placement at remote background air monitoring sites.