Treating styrene in the atmosphere
Spraying another compound to neutralize styrene (which is difficult) or whatever it was is probably not helpful, as it takes too long to spread and other potentially harmful materials are introduced, as one would need to apply the substance in excess. 

Having readily installed outlets for water curtains at the plant might be helpful. The quickest emergency measure would have been if every household in the area was equipped with sufficient amounts of respirators and suitable absorbers ("filters") and training the people how to use them correctly (and teaching them that the absorbers have a limited capacity) might give enough time to escape. This would be a good and rather cheap provision for the future. Otherwise ventilation to dilute the materials is the only thing one can do, I'm afraid.