Quan tinc mal al nas, sempre porto un mocador a la bossa.

Because Catalan usually drops subject pronouns when the verb already makes the subject clear.

• tinc = I have
• porto = I carry / I take / I wear, depending on context

So Quan tinc mal al nas, sempre porto... already clearly means When I..., I always...

You can add jo for emphasis or contrast:

• Jo sempre porto un mocador... = I always carry a handkerchief...

But in a neutral sentence, leaving out jo is more natural.

Here quan has the sense of when / whenever.

Because the sentence describes a habitual situation, English often translates it more naturally as whenever:

• Quan tinc mal al nas, sempre porto un mocador...
• Whenever my nose hurts, I always carry a handkerchief...

So quan can introduce:

• a specific time: When I arrive, call me
• a repeated situation: Whenever I have a headache...

In this sentence, it is the repeated, habitual meaning.

Catalan often uses the present tense to talk about general habits or things that happen regularly.

So:

• Quan tinc mal al nas = when/whenever my nose hurts
• sempre porto un mocador = I always carry a handkerchief

This is just like English using the present for routines:

• When I feel sick, I stay home
• If it rains, I take an umbrella

It is not talking about only one moment right now; it is describing a pattern.

Catalan often expresses pain with tenir mal a + body part.

So:

• tinc mal al nas = I have pain in my nose / my nose hurts

This is a very common structure:

• tenir mal al cap = to have a headache
• tenir mal a l'esquena = to have back pain
• tenir mal a la cama = to have a pain in the leg

Another very common Catalan way to say the same thing is:

• Em fa mal el nas

That literally works more like My nose hurts me or The nose does pain to me, but in normal English it is simply My nose hurts.

So both are natural:

• Tinc mal al nas
• Em fa mal el nas

Al is the contraction of a + el.

So:

• a + el = al

That means:

• mal al nas = pain in/to the nose

This contraction is very common in Catalan:

• Vaig al mercat = I go to the market
• Tinc mal al peu = My foot hurts / I have pain in my foot

If the noun were feminine, you would not get al:

• mal a la mà = pain in the hand

And before a vowel:

• mal a l'orella = ear pain

With body parts, Catalan often uses the definite article instead of a possessive adjective when the owner is already clear.

So Catalan prefers:

• em fa mal el nas
• tinc mal al nas

rather than constantly saying:

• el meu nas

English usually says my nose, but Catalan often says the nose in these contexts because it is obvious whose nose is being discussed.

This is very common:

• Em rento les mans = I wash my hands
• M'he trencat la cama = I broke my leg

So el nas is completely normal here.

Yes, absolutely.

These are both natural:

• Quan tinc mal al nas, sempre porto un mocador a la bossa.
• Quan em fa mal el nas, sempre porto un mocador a la bossa.

They mean almost the same thing.

A simple way to think about them is:

• tenir mal a... = to have pain in...
• fer mal = to hurt

So:

• Tinc mal al nas = I have pain in my nose
• Em fa mal el nas = My nose hurts

Both are common and correct.

Portar is a very flexible verb in Catalan. It can mean different things depending on context:

• carry
• bring
• wear
• sometimes even take along

In this sentence, porto un mocador a la bossa means something like:

• I carry a handkerchief in my bag
• I keep a handkerchief in my bag

So here porto is about having it with you.

Examples of other meanings:

• Porto una jaqueta = I’m wearing a jacket
• Porta el llibre a classe = Bring the book to class

Here mocador means handkerchief.

But learners should know that mocador can have a broader range of meanings depending on context. In different situations it can refer to:

• a handkerchief
• a scarf
• a headscarf

Because this sentence mentions nose pain, the intended meaning is clearly something used for the nose.

If you want to be very specific about a paper tissue, Catalan may say:

• mocador de paper

In some places you may also hear other words for tissue, depending on regional usage.

Catalan often leaves out the possessive when it is already obvious from the context.

So:

• porto un mocador a la bossa

naturally means something like:

• I carry a handkerchief in my bag

Because the speaker is talking about what they personally carry, it is easy to understand that la bossa is their bag.

If you want to emphasize it, you can say:

• a la meva bossa = in my bag

But the shorter version is very natural.

Catalan often uses a in places where English would use in.

So a la bossa is a normal way to say:

• in the bag
• inside the bag
• sometimes more loosely, with me in my bag

If you want to stress the idea of being physically inside, you can say:

• dins de la bossa

But in everyday Catalan, a la bossa is perfectly natural after a verb like portar.

Not exactly, because quan and si do different jobs.

• quan = when / whenever
• si = if

In your sentence, quan suggests that this is a situation that happens from time to time, and whenever it happens, the speaker does the same thing.

• Quan tinc mal al nas, sempre porto un mocador...
  = Whenever my nose hurts, I always carry a handkerchief...

If you said:

• Si tinc mal al nas, sempre porto un mocador...

it would sound more conditional, closer to:

• If my nose hurts, I always carry a handkerchief...

That is not impossible, but quan is more natural for a repeated habit.

Because the sentence begins with a subordinate clause:

• Quan tinc mal al nas = introductory time clause

Then comes the main clause:

• sempre porto un mocador a la bossa

In writing, Catalan often uses a comma after this kind of introductory clause, especially when it comes first. It helps the sentence read more clearly.

So:

• Quan tinc mal al nas, sempre porto un mocador a la bossa.

is a normal and well-punctuated sentence.