Reports are that Syria may be producing Sarin gas. Sarin is a nerve agent that is usually not mixed until it is required since it is highly corrosive, volatile and dangerous. Sarin gas was used by Aum Shinrikyo to attack the Tokyo subway in 1995. Turkey had earlier requested the Patriot missile system in anticipation that Syria would start using chemical weapons against the rebels.
Chemical weapons are imprecise. Winds and other meteorological factors can reduce or even neutralize the weapon before it effects people. Chemical weapons tend not to be pervasive and it is hard to concentrate enough to be effective on a wide area to produce mass casualties. Sarin is extremely deadly, a mere drop will kill a human.
Chemical weapons are then much more about the psychological impact then about gaining any military advantage. You risk poisoning your troops just as much as your enemies. The Assad government is obviously feeling the rebels may be getting the upper hand and wants to inflict a psychological blow to the moral of the rebels. Assad may also be giving a middle finger to the Western world that he would do something so reprehensible.
The United States is not helping matters by alternating focus between Iran and Syria. At the same time, major changes are occurring at CIA, State and DoD. It may be seen as an opportunity to take advantage of the US going through a period of transition.
The continued focus on Iran's nuclear program will be seen by some as forcing Syria to escalate into chemical weapons. We may also see Syria cells activated in the US threatening to use chemical weapons or cyber attacks. Iran has remained somewhat quiet in the last year but may also have cells that will be activated in the US. We are going into the holiday season and with multiple college bowl games and the Super Bowl coming up, there are soft targets that could be threatened by a terrorist attack.