Atmospheric CO2 is currently around 430 ppm. It's minimally variable based on seasonality, think a 15 ppm difference between the lowest and highest points.
It's been a long time since University for me but the standard measurement location is the Mauna (sp?) Loa Observatory in Hawaii, if I recall correctly due to it being the longest-running continuous measurement site.
It's been a long time since University for me but the standard measurement location is the Mauna (sp?) Loa Observatory in Hawaii, if I recall correctly due to it being the longest-running continuous measurement site.