The unweighted bounce average (Nj) of the atmospheric density Nj along a field line and the weighted bounce average ⟨ (B0/B) Nj cos2 &agr;⟩ are related (for each atmospheric constituent j) by an integral or derivative with respect to y, the sine of the equatorial pitch angle &agr;0, where B/B0(=y-2 sin2 &agr;) is the ratio of local to equatorial magnetic field intensity and &agr; is the local pitch angle. The unweighted bounce average ⟨Nj⟩ is relevant to energy deposition by radiation belt particles of all species, while the weighted bounce average ⟨ (B0/B) Nj cos2&agr;⟩ is relevant to the description of pitch angle diffusion of radiation belt electrons.