"Down slope winds sometimes transport these emissions to the observatory, where they are detected as a "noisy" increase above smooth baseline levels for some gases. A volcanic component can be estimated by taking the difference in concentration between periods when the plume is present and periods immediately before and after that exhibit baseline conditions."
and
"The CO2 emission rate follows a very predictable exponentially decreasing trend which is established after each eruption. The slope of these trends have been different for each eruption. Current concentrations of volcanic CO2 (2006) are at their lowest levels since the record began in 1958."
“Current concentrations of volcanic CO2 (2006) are at their lowest levels since the record began in 1958.”
This is tricky because Mauna Loa hasn’t erupted since 1984.
Pu`u O`o is on Kilauea and has erupted non-stop since 1983. They are playing games here.
Here are some details of the Pu`u O`o eruption:
Kilauea emits about 3.3 million tonnes/year of CO2
concentrations as high as 48.9% CO2 have been measured at Kilauea summit
Good read:
http://volcanoes.usgs.gov/Hazards/What/VolGas/volgas.html#reference