Indeed, you weren't even in China back then
Interesting though there seems to be a bit of a dispute on that.
Chemical warfare used since 4000BC
The ancient Chinese used arsenic compounds in smoke bombs as far back as 1000 BC. They called the deadly smoke a “soul-hunting fog.”
Ancient Warfare - Chemical Warfare in the Ancient World: Part 1 - Fight Times Magazine
The Chinese were also the first to exploit poison gas.As early as the 4th century B.C. the Chinese used noxious smoke to defend besieged cities.As the attackers attempted to undermine the city walls the defenders would attempt to tap into their tunnels with terracotta pipes.Then a bellows would be used to pump in smoke and noxious gas from a nearby furnace, causing fits, poisoning, suffocation and death in the enemy miners.
Arsenic smoke was also used by the Spartans during the sieges of Plataea and Delium in the Peloponnesian War. 431-404BC.
Ok, more on that. i think the first use of that was the Tartar army which catapulted plague victims over the city walls during the siege of Caffa.
Plague at the Siege of Caffa, 1346
The first stage of the Black Death among Europeans was said to begin with the whoosh of a Mongol trebuchet. Gabriele De’ Mussi, a lawyer from near Genoa writing in about 1348, is believed to have recorded the account of the earliest use of plague asweapon of war at Caffa in 1346.
This was then used as a common weapon of war from 1346 - 1710.
Good ol' homo sapiens - they don't change much over the years.
400BC Filling an opponents tunnels with smoke and the CO associated with it ? perhaps, which they later refined with arsenic ? @Sonic67