Chemical weapons are chemical agents of warfare taken to be chemical substances, whether gaseous, liquid, or solid, which might be harmful because of their direct toxic effect on human, animals, and plants. A chemical agent is a chemical substance, which is intended for use in military operations to kill or seriously injure people because of its physiological effects. Chemical weapons can be classified into two main categories by their instability, persistent and non-persistent agents. .
A persistent agent continues to present a hazard for a considerable period of time after its delivery. It remains as a contact hazard or by vaporizing over a period of time to produce a hazard by inhalation. A non-persistent agent breaks up rapidly after its release and presents an immediate but short-lived hazard. They are released as airborne particles, liquids and gasses. Intoxication usually results from the inhalation of the chemical agent. .
The effectiveness of a chemical weapon is the capacity of an agent to produce the maximum number of casualties or amount of disruption of operations with the least amount of agent. There are many factors that can influence the effectiveness of a chemical agent: such as the amount of the agent release, environmental factors, population size and more. The duration of effectiveness for a chemical agent depends on several meteorological factors such as: .
Winds- Winds allow chemical agents to disperse rapidly in certain locations. Lack of wind can cause a build up in the concentration of certain chemical agents. .
Temperature- High temperatures tend to decrease the persistency of some agents while cold temperatures tend to increase the persistency of some agents. .
Rain- Rain effects chemical agents by disposing some or by promoting hydrolysis in some agents. Overall rain may dispose of some particular agents but others will most likely still be able to be used. .
Atmospheric Stability- When the temperature of the air is higher than that of the ground; chemical agents in a vapor state tend to stay persistent for longer periods of time.