The literature on atmospheric CO2 levels seems to be based only on the monitoring by Mauna Loa Observatory. Are there any other CO2 monitoring stations in the world?
Yes, atmospheric CO2 is monitored by stations other than Mauna Loa. Some of these include Cape Grim in Australia, Jungfraujoch in Switzerland, and Arctic Station Alert in Canada.
The Mauna Loa site was chosen because it was well away from industrial pollution. It is the longest record and the site, near the equator, has been found to give results similar to the global average.