There's no H2S in propane, although there's a little methyl mercaptan in it as an odourant so it "smells of gas". As for the NOx emissions I'm not sure why it'

There's no H2S in propane, although there's a little methyl mercaptan in it as an odourant so it "smells of gas". As for the NOx emissions I'm not sure why it's lower as in theory it should burn hotter - LPG runs lean which is why there's no CO, but that should make more NOx.