Square brackets around CO2

Question

This is probably a silly question, but there is a text about photosynthesis which talks about carbon dioxide all the time, but only in one opportunity does CO2 appear inside square brackets. Does it mean anything in particular?

I'll leave you the sentence:

"In our original model, RuBP regeneration was controlled by electron transport, but could also be limited further by other components of the photosynthetic carbon reduction cycle. At higher [CO2], Tom has drawn attention to a third limitation that may come into play, that of triose phosphate utilization."

Answer 1

In chemistry and/or biochemistry, when something appears in square brackets [  ], this represents CONCENTRATION, and the concentration is usually (but not always) in moles/liter.