[Crazy Dazz]

Original Secondary Air Injection technology goes back to the 60's and 70's. I remember that back in the 80's my brother's wife had a Mini with this feature.
In those days the engine was tuned a bit rich, and a compressor or pump injected air into the exhaust manifold, to burn up excess hydrocarbons and carbon monoxide.

With the advent of catalytic convertors, SAI was used only for a very specific purpose. When the Cat was cold, the engine would run in rich phase, BUT inject air upstream of the cat, with the burn increasing the temperature and heating the cat quickly to operating temperature.

It's hard to imagine, but I guess in countries where you routinely drive in sub zero temperatures, keeping your Cat at operating temperature may be a huge issue. (Especially perhaps when crawling in traffic at low power?)

Some cats also use secondary air, injected directly into the cat itself.