  A survey of the data on measured particle fluxes and the rate of ionization
in the atmosphere is presented. Measurements as a function of altitude, time
and cut-off rigidity are compared with simulations of particle production from
cosmic rays. The simulations generally give a reasonable representation of the
data. However, some discrepancies are found. The solar modulation of the
particle fluxes is measured and found to be a factor 2.7$\pm$0.8 greater than
that observed for muons alone near sea level.
