A chemical weapons expert involved in the apparent discovery of continued chemical weapons attacks in Syria told ITV News earlier this week that chlorine use is "simple to identify".
Hamish De Bretton-Gordon told Diplomatic Correspondent John Ray that Syrians should be armed with information on how to identify such attacks.
He added, however: "It's very, very non-persistent - once it's released it will remain active for, at the most, minutes.
"If there is a strong wind and if it is hot as it is in Syria it will disappear very quickly."
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A cloudy and damp start for many southeastern areas, but turning brighter through the afternoon.