Most gasses are odorless, all odors are particulate, and the gas over a graveyard is unlikely to be any different than the gas over your head at right this instant.
Methane, an odorless gas, is generated by decomposing biomass, and could perhaps be the gas that you are thinking of. It can cause ghostly glows if ignited (by static electricity for instance.)
Methane is the gas present in coal mine.
A graveyard is fog.
The ozone gas present in the atmosphere absorbs ultraviolet radiations. This gas is present in the form of ozone layer in the atmosphere.
LPG contains petroleum gas.
If you are absolutely certain there was no gas present tell your Doctor, its not uncommon for people with brain tumours to smell gas that is not present.
The graveyard is silent.
is there a general lee graveyard?
Methane
amonia
Freon
The main gas present in ozone layer is ozone gas. It is present in the stratospheric region of atmosphere.
They are in the Graveyard, Founder's Graveyard.