I'm doing a school project on cosmic rays (using data from the HiSPARC database), and we need to be able to calculate the average temperature of the atmosphere above specific cities on a specific date to input into the Ideal Gas Equation (PV=nRT). We are trying to find an estimate for the number of molecules between the detectors and space, which is where the proton emitted breaks down into the parts which are detected, so that we can create a mathematical model which can calculate an estimate for the number of cosmic rays detected by a detector in a day. I've looked around, but nowhere tells me a way to do it, including other questions on this site. We've decided to do one effect at a time, so there may be more questions like this in the future. Can anyone help me?
Good news - thanks to those that gave answers I have values for the number of molecules. This question is answered! (Watch me for others soon: possibly clouds and such)