The format is:
List of 5
$Z
:'data.frame': 730 obs. of 68 variables: Ozone ppb for 68 sensors.
$locs
:'data.frame': 68 obs. of 2 variables: longitude, latitude for 68 sites.
$helevs
: elevations (meters) for 68 sites.
$locs0
: 2358 obs. of 2 variables: longitude, latitude for interpolation grid.
$helevs0
: elevations (meters) for 2358 interpolation grid sites.