Whatever tech was used to this end would have to be a huge invasion of privacy.
I think it's technically possible to use powerful technology while preserving privacy - but those in power don't do that.
A good website should keep its users passwords secret even from admins... but do they? Similarly a powerful private system could be listening to you all the time, but essentially not tell anyone except for for previously agreed-on and widely known circumstances.
We can now detect the presence of a species of animal in a region by 'sniffing' its DNA in the air. Sensing and zeroing in on sources of cocaine should be trivial in comparison.
Of course I hope nobody's going to cry 'privacy' if their house is clearly ground zero for cocaine residue floating through a neighborhood.
Human nature is endangered - fighting it is soon to become trivially easy, if it's not already. The technology we now have is enabling absolute societal control, and far from nobody having the balls to do what's necessary, it looks like a smooth slide towards a full nightmare dystopia.
I think eliminating the cocaine trade is something quite doable with modest technology and minimal human rights violations, and is something I could support. Unfortunately those in charge don't seem to be capable of doing something like that without abusing their power so that the net effect is far more detrimental to society.