  Decays of mesons produced in cosmic ray induced air showers in Earth's
atmosphere can lead to a flux of light exotic particles which can be detected
in underground experiments. We evaluate the energy spectra of the light neutral
mesons $\pi^0$, $\eta$, $\rho^0$, $\omega$, $\phi$ and $J/\psi$ produced in
interactions of cosmic ray protons and helium nuclei with air using QCD
inspired event generators. Summing up the mesons produced in the individual
hadronic interactions of air showers, we obtain the resulting fluxes of
undecayed mesons. As an application, we re-consider the case of millicharged
particles created in the electromagnetic decay channels of neutral mesons.
