Effective energy loss per electron-ion pair produced, (E0), as a function of a particle's initial energy has been obtained for proton transport in the atmosphere. The influence of some transport parameters on the shape of (E0) has been studied. Comparisons with the case of electron transport and with other results were made. It has been shown that: 1. for E0>1 keV, (E0) varies within the range 30-36 eV; 2. as E0 increases the value of (E0) tries to attain an asymptotic value that is the same as for electrons (≈35 eV); 3. (E0) strongly depends on the average energy of secondary electrons, but the energy distribution of secondary electrons is not as important. The range of possible changes in (E0) associated with discrepancies in cross sections has been obtained.