Thanks Gary.Very interesting.On this forum,about two years ago, Dave Gardner put a letter that he had written to the Guardian,about the first scientist to analyse the CO2 content of the air.Unfortunately it is not now in the archives.He gave some value examples and they did seem on the high side.
It is said that the accuracy of these chemical methods was of the order of 3%.Presumably it would be straightforward to replicate the kit originally used and verify this,
That's right, I wrote a letter (an e-mail actually) to the Guardian after they published an obituary for Charles Keeling in 2005. The Guardian environment correspondent, Paul Brown, claimed that Keeling's big innovation in the late 1950s was to measure background CO2 levels for the first time, using the famous Mauna Loa location. I pointed out that a British scientist, Angus Smith, inventor of the concept of "acid rain", had measured background CO2 levels nearly 100 years earlier in the 1860s on the summit of Ben Nevis in Scotland.
The Ben Nevis value in the 1860s was 327 ppm, quite a bit higher than the 290 ppm claimed from ice core data for this time. I think Grant also came up with a figure of something like 334 ppm measured by Angus Smith for the moors of Scotland from some old book he had.
It's also possible to show that rural Scotland is a pretty good at giving very similar values to Mauna Loa in recent times:
Shetland Islands, Scotland (elevation 30m)
CO2 risen from 356.89 ppm in 1993 to 370.97 ppm in 2001
From 1993 to 2001 Mauna Loa CO2 rose from 357.04 ppm in 1993 to 371.02 ppm in 2001.
This suggests that isn't necessary to go to exotic locations like Mauna Loa and the South Pole to measure ambient CO2 levels.