There are a huge number of problems with atmospheric CO2 measurements between 1850 and ~1960 when Keeling introduced IR absorption based instrumentation. They can be summarized as not paying attention to detail. Paying attention to detail was Keeling's strength. Let's start from the beginning. You first have to understand and thoroughly characterize the location where you are making the measurements. This involves taking measurements at all times of day and year and correlating with winds, vegatation and many other things. Keeling, for example, found that when the winds blew from LA to La Jolla, his measurements were higher. He also found effects from the respiration of the vegatation at different times of day. There are some areas which are totally inappropriate. Paris is one, Essen another. One of my posts links to a CO2 measurement done while moving through the Ruhr. You can easily get high measurements. Then, of course, you have to sample the air. The IR method allows you to continuously sample, but before that you had to grab a sample by sucking it into something. This is very tricky, and of course there are any number of dumb ways of doing this of which Mr. Roland Ploennige's playing the Fronselius trombone has to be the worst. Compare this with the careful way that Keeling describes how the gathered grab samples at the same link. Preparation of the sample volumes and their storage is also vital. For example, Keeling found that exposure of the glass bulbs he used was using to light for a couple of weeks produced an artifact. Of course, you want the largest possible volume to minimize surface effects and give you material to work with. Then you need a method. Beck is delusional about the wet chemistry methods. At best they are a few percent in the hands of an expert, but they easily can give bad readings if not done perfectly. The IR method has all the advantages of an instrumental measurement. Since readings can be taken frequently, it is easy to build a statistical distribution that characterizes each sample. The titrations take a long time and require much more sampled material so one cannot get nearly the number of measurements from a single grab sample. As Keeling commented This Scandinavian program, started by Rossby in 1954, had been a major factor in triggering interest in measuring CO2 during the IGY. Nevertheless it was quietly abandoned after the meeting, when the reported range in concentrations, 150–450 ppm, was seen to reflect large errors. 3 3. At two stations in Finland, samples collected by station personnel had been sent to Scripps. These samples yielded nearly the same concentrations as those measured at Mauna Loa Observatory, proving that the errors in the Scandinavian program were mainly analytical rather than due to variable CO2 in the air being sampled. Calibration is, of course the key. Several of Beck's cited references do not mention how they calibrated their measurements. To make matters worse, you want to calibrate with mixtures that you know the concentration of the CO2 in as exactly as possible and making such mixtures at the ppm level, and maintaining them is a magical art as anyone who has tried it knows. In the instrumental system, calibrations are done interleaved with the measurements, think about how you would do this with a titration. One could go on at length, and I suppose when I have some more time I will, but in short it would be amusing to give the Good Diplom Beck a couple of well characterized grab samples to analyze by titration. For Z I refer you to Some Are Boojums