Learn Hardcore Portuguese (Portugal): Durante a pandemia, eu uso sempre máscara no autocarro. - During the pandemic, I always wear a mask on the bus.

In Portuguese, the present tense is used, like in English, for habits that are true in a general time frame (including a period that is still going on).

Eu uso sempre máscara no autocarro.
= I always wear a mask on the bus. (habit, a general rule)

You would use:

usei (preterite) for a completed action:
Durante a viagem, eu usei máscara.
During the trip, I wore a mask. (one finished trip)
usava (imperfect) for a past habit that no longer applies, or when the pandemic is clearly over in the speaker’s mind:
Durante a pandemia, eu usava sempre máscara no autocarro.
During the pandemic, I always wore a mask on the bus. (a past routine, now finished)

In your original sentence, the speaker is describing a general rule that applies during the pandemic period, seen as a still-relevant or “current” habit, so uso works naturally.

Do I have to say eu? Can I just say Durante a pandemia, uso sempre máscara no autocarro?

You do not have to say eu. In Portuguese, the verb ending already shows the subject:

uso = I wear
usas = you (tu) wear
usa = he/she/you (você) wears

So:

Durante a pandemia, uso sempre máscara no autocarro.
is perfectly correct and quite natural.

Including eu:

Durante a pandemia, eu uso sempre máscara no autocarro.

adds a bit of emphasis, like saying “I always wear a mask…” (maybe contrasting with other people who don’t). In neutral speech, many Portuguese speakers would omit eu here.

Why is it máscara without an article? Could I say uma máscara or a máscara?

All three are grammatically possible, but they sound slightly different:

uso sempre máscara
– Very natural in European Portuguese for general habits with certain nouns (especially clothes, accessories, etc.).
– Similar to English “I always wear gloves” vs “I always wear a pair of gloves.”
– It focuses on the activity, not on one specific item.
uso sempre uma máscara
– Literally “I always wear a mask.”
– Perfectly correct. More explicit that you are talking about a (one) mask each time.
– Common in both European and Brazilian Portuguese, perhaps more neutral for learners.
uso sempre a máscara
– Literally “I always wear the mask.”
– Refers to a specific, already-known mask (for example, “the mask the doctor gave me”).
– Less likely in a general statement about your normal behaviour, unless the context has clearly introduced that particular mask.

So your original uso sempre máscara is natural European Portuguese meaning “I (habitually) wear a mask.”

Where can I put sempre in this sentence? Are eu sempre uso máscara or eu uso máscara sempre also correct?

Yes, several word orders are possible, and they’re all grammatically correct, with small differences in emphasis:

Durante a pandemia, eu uso sempre máscara no autocarro.
– Very natural. sempre comes between verb and object.
– Neutral, common pattern: verbo + sempre + objeto.
Durante a pandemia, eu sempre uso máscara no autocarro.
– Also natural. sempre before the verb.
– Slight extra emphasis on always: “I always wear a mask…”
Durante a pandemia, eu uso máscara sempre no autocarro.
– Grammatically OK, but sounds less natural here.
– It can sound like you’re limiting sempre to “on the bus” (as opposed to other places).
Durante a pandemia, eu uso máscara no autocarro sempre.
– Possible, but marked and unusual; again, it tends to emphasise “always on the bus.”

The most typical European Portuguese options are uso sempre máscara and sempre uso máscara. The original sentence is perfectly idiomatic.

Why is it no autocarro and not something like em o autocarro?

no is the contraction of em + o:

em = in / on / at
o = the (masculine singular)

So:

em + o autocarro → no autocarro

This is obligatory: in normal speech and writing you do not say em o autocarro, you must contract to no autocarro.

Similarly:

em + a carrinha → na carrinha
em + os autocarros → nos autocarros
em + as carrinhas → nas carrinhas

Does no autocarro mean “on the bus” or “in the bus”? How does em work here?

Portuguese em covers what English divides into in, on, and sometimes at. Context tells you the exact English equivalent.

no autocarro literally: “in/on the bus”
In this context, in natural English we say “on the bus,” so we translate it that way.

Other examples:

no comboio – on the train
na escola – at school / in the school (depends on context)
no restaurante – at the restaurant / in the restaurant

So no autocarro is the standard way to say “on the bus” (when you are travelling by bus or physically inside it).

What is the difference between no autocarro and de autocarro?

They answer slightly different questions:

no autocarro – focuses on location: “on / in the bus”
- Uso máscara no autocarro.
  I wear a mask on the bus. (while I’m on it)
de autocarro – focuses on means of transport: “by bus”
- Vou para o trabalho de autocarro.
  I go to work by bus.

You could combine them:

Durante a pandemia, vou para o trabalho de autocarro e uso sempre máscara no autocarro.
During the pandemic, I go to work by bus and I always wear a mask on the bus.

Why is it autocarro and not ônibus? Are they the same?

Yes, they refer to the same thing but in different varieties of Portuguese:

autocarro – standard in European Portuguese (Portugal)
ônibus – standard in Brazilian Portuguese

So in Portugal you say:

Vou de autocarro. – I go by bus.

In Brazil you say:

Vou de ônibus. – I go by bus.

Since you are focusing on Portuguese from Portugal, autocarro is the right word.

Why is it a pandemia and not o pandemia? How do I know pandemia is feminine?

pandemia is feminine because of its -a ending, which is a very common marker of feminine nouns in Portuguese.

a pandemia – the pandemic
a mesa – the table
a cadeira – the chair

There are exceptions (e.g. o problema, o mapa), but as a general rule:

-a ending → usually feminine → a
-o ending → usually masculine → o

So:

Durante a pandemia… – During the pandemic…

Can I say ponho sempre máscara or visto sempre máscara instead of uso sempre máscara?

For “wear” in the sense of “have on (clothes, accessories),” usar is usually the safest and most general verb:

uso sempre máscara – I always wear a mask.

The other verbs are more specific:

pôr (ponho) – to put, to put on (the act of putting something in place)
- Ponho a máscara antes de entrar.
  I put the mask on before going in.
  It describes the action of putting it on, not so much the ongoing state of wearing it.
vestir (visto) – to dress, to put on clothes
- Typically used with clothing you “put on your body” like shirts, coats, trousers:
  visto o casaco, visto a camisa.
- With máscara, vestir is unusual. You would not normally say visto máscara.

So:

For “I always wear a mask,” stick with uso sempre máscara.
To emphasise the action of putting it on: Ponho sempre a máscara antes de entrar no autocarro.

Could I say Durante a pandemia, estou sempre a usar máscara no autocarro? Is that different from eu uso sempre máscara?

Yes, you can say it, and there is a subtle difference:

Uso sempre máscara no autocarro.
– Simple present, a general habit. Very direct and standard.
Estou sempre a usar máscara no autocarro.
– Present progressive (European style), literally “I am always using a mask on the bus.”
– Often used to highlight the continuity or repetitiveness of an action.
– It can sound like you are stressing how constant or maybe even annoyingly constant the action is (depending on tone and context).

In most neutral statements about your routine, uso sempre máscara is more common and natural.

Is the stress really on the first syllable in máscara? How is it pronounced?

Yes. máscara has the stress on the first syllable:

MÁS-ca-ra

The written accent (´) over á shows that this is the stressed vowel and also tells you that the word is not stressed on the usual last or second-to-last syllable.

European Portuguese pronunciation (simplified):

má – like “mah” (short, not very open in European Portuguese)
sca – the s is like English “s”; c before a is a hard k sound: “ska”
ra – “ruh” with a European Portuguese r that can sound like a guttural or uvular sound, often similar to French r.

Approximate: MAHS-ku-ruh (EP).

Is it OK to move durante a pandemia to the end: Eu uso sempre máscara no autocarro durante a pandemia?

Yes, it is grammatically correct:

Eu uso sempre máscara no autocarro durante a pandemia.

However, putting durante a pandemia at the beginning is more natural and common when you want to set the time frame first and then describe your habit:

Durante a pandemia, eu uso sempre máscara no autocarro.

Both are understandable; starting with Durante a pandemia sounds more fluent in this kind of general statement.