Upon: ao

avenida-brasil

You're already using "ao" to say at the or, to the, but it has another entirely different meaning when used together with a verb in the infinitive. When I first started hearing people say this I didn't even notice t since it's just an "ow" before of a verb. I though it was some weird slang.

It's not.

When you say ao+verb in the infinitive, you are saying either: on, when, or as soon as

So to say for example, upon arriving... it's: ao chegar...

This is very cool! Let's see some examples:

Upon opening the box it was obvious that it was something fragile.

Ao abrir a caixa, ficou óbvio que era algo frágil.

Upon finding out that she was married, he took off (went away).

Ao descobrir que ela era casada, ele foi embora.

Upon seeing the mess he made, I decided to call for some professional help.

Ao ver a bagunça que ele fez, decidi chamar uma ajuda 'pro'.

Upon hearing that story, I swore-off alcohol.

Ao ouvir a história resolvi nunca mais beber.

Upon turning the corner, she looked over her shoulder and saw her friend walking.

Ao dobrar a esquina ela olhou pelo ombro e viu sua amiga andando.

Upon seeing them together, he knew it was over.

Ao vê-los juntos, ele soube que acabou.

Upon becoming a young man, he already had an arrest record.

Ao se tornar um garoto, ele já tinha passagem pela polícia.

*Notice that in English we can say either upon arriving or, upon arrival. I have no idea why. In Portuguese these both translate as ao chegar.

Upon arriving home, I noticed that all the lights were on.

Ao chegar em casa reparei que todas as luzes estavam acesas.

Upon arrival, we went straight to the airline gate.

Ao chegar, fomos direto ao portão (do avião).

You can also use ao to say at like this:

Mas aos 5 anos nós viemos para cá. (at five years of age...)

From the video learning course, INTENSIVO.