| a
| Aircraft
| Large representative area due to high altitude above ground
|
| (none)
| Height above ground
|
| b
| Surface,
baseline
| Same as "r"
| Same as "r"
| (none)
| Height above sea level
|
| c
| Surface,
complex (continental) circulation
| Difficult for transport model, but still regionally representative
| Higher than "r"
| For continuous in-situ records, mostly use day-time values only
| Height above sea level
|
| m
| Surface,
high mountain
| During night-time, sampling location sticks into free troposhere, thus representative for larger area than "c"
|
| For continuous in-situ records, use night-time values
| Height above sea level
|
| o
| Ocean shipboard
| Moving, conditions comparable to "r"
| Same as "r"
| (none)
| Height above sea level
|
| r
| Surface,
remote (e.g. islands)
| Large-scale representative, little local influence
|
| (none)
| Height above sea level
|
| s
| Surface,
at shore with more complex circulation
| Unsuitable for class "r"; alternating land and ocean footprint, possibly sea-breeze systems
| "r" < "s" < "c"
| (none)
| Height above sea level
|
| t
| Tall tower
| Due to tower height, potentially representative for larger area than "c"
| Nevertheless, currently same sigma as "c".
| As "c"
| Height above ground
|
| u
| Urban
| Highly polluted, complex circulation
| Much higher than "r" (not normally used in global inversions)
|
|
|