Dear Vaibhav,

The concentration of CO2 in the atmosphere is highly variable in space and time due to emission, chemistry, transport, and deposition.

The exact concentration of it may not be possible because of the lack of calibrated global observations and the models used to quantify have huge holes as of now both in meteorology and chemistry. I don't touch upon meteorology here but the chemistry is very limited. CO2 is the end product of atmospheric oxidation of various emissions (known and many unknown), but many of the emissions and their chemistry to form CO2 in the atmosphere is very limited as of now.

Hope this helps!

Yes Dr. Kishore but can we tentitively estimate considering biological mass.

I am not sure but you may explore satellite-derived photosynthetic active radiation (PAR) to get a good correlation with CO2.

Yes, this is some what we correlate the things with PAR