Chlorine gas is over twice as heavy as air. No bombs necessary.
Chlorine gas is some nasty stuff. Easy to make, easy to deploy, and causes a horrible death. Upon exposure to chlorine gas, you will drown in your own body fluids, which is caused by your lungs attempting to dilute the absorbed gas by producing fluid and mucus to counteract inhaling the gas.
These missile strikes weren’t meant so much as to curtail the production of chlorine, as much as destroying the methods of weaponizing it for use on the populace, or anyone for that matter.