Learn Hardcore Portuguese (Portugal): Quando o ar está seco, sinto mais irritação na garganta. - When the air is dry, I feel more irritation in my throat.

o ar literally is the air, but in many contexts it just means air in general.
English: When air is dry…
Portuguese: Quando o ar está seco…

So o ar doesn’t mean a specific, particular air here; it’s just how Portuguese typically talks about things in general (the air, the water, the body, the life, etc.). Leaving out the article (Quando ar está seco) is ungrammatical in this sentence.

Why is it está seco and not é seco?

Both ser and estar translate as to be, but:

ser is used for permanent/defining characteristics.
estar is used for temporary states or conditions.

Dry air is a temporary condition, depending on the weather or the environment, so you use estar:

Quando o ar está seco… = When the air is (temporarily) dry…

If you said:

Quando o ar é seco…

it would sound more like you’re talking about a place whose climate is characteristically dry, a more permanent property. In everyday speech about changing humidity, está seco is the natural choice.

Why is it just sinto and not eu sinto?

Portuguese is a pro‑drop language: you can usually omit the subject pronoun (eu, tu, ele…) because the verb ending already tells you who the subject is.

eu sinto = I feel
sinto on its own is still clearly I feel, because of the -o ending on sinto (1st person singular).

Both are grammatically correct:

Quando o ar está seco, sinto mais irritação na garganta.
Quando o ar está seco, eu sinto mais irritação na garganta.

Adding eu emphasizes I (contrasting with others, or stressing your experience). The version without eu is more neutral and very typical.

What tense are está and sinto, and why is that used with quando?

Both está and sinto are in the present indicative:

está = he/she/it is (temporary state)
sinto = I feel

In Portuguese, for general truths or things that regularly happen, you often use the present in both clauses with quando:

Quando o ar está seco, sinto mais irritação na garganta.
= When the air is dry, I feel more irritation in my throat (whenever that happens).

In English you also have present in both clauses (When the air is dry, I feel…), so the logic is similar here.

Why is it sinto mais irritação and not something like sinto-me mais irritado?

You have two common patterns in Portuguese:

sentir + noun
- sinto mais irritação na garganta
  Literally: I feel more irritation in (my) throat.
  Here irritação is a thing you feel.
sentir-se + adjective
- sinto-me mais irritado / irritada
  Literally: I feel more irritated.
  Here irritado(a) is how you feel.

The original sentence focuses on a symptom located in the throat and treats it as a noun (irritação). If you want a more “personal feeling” version, you could say:

Quando o ar está seco, sinto-me com a garganta mais irritada.
(When the air is dry, I feel my throat is more irritated.)

Both are correct; they just highlight different aspects.

What exactly is na garganta? Why not just em garganta or da garganta?

Na is a contraction of em + a:

em = in / on / at
a = the (feminine singular)
em + a → na

So:

na garganta = em a garganta = in the throat / in my throat

In Portuguese you must use the article in this type of expression:

✅ irritação na garganta
❌ irritação em garganta

da garganta would mean of the throat, which would sound odd here:

irritação da garganta = irritation of the throat (more like “the throat’s irritation”, not what you want).

Why is it irritação (a noun) instead of an adjective like irritada?

Portuguese can express symptoms either as:

a noun: irritação, dor, sensação, etc.
an adjective: irritada, dolorida, etc.

The sentence uses the noun pattern:

sinto mais irritação na garganta
= I feel more irritation in my throat.

If you used an adjective, it would be something like:

sinto a garganta mais irritada
= I feel that my throat is more irritated.

Both are idiomatic; sinto mais irritação na garganta just chooses the “I feel more irritation (noun)” structure.

Why does seco end in -o here? Does it agree with ar?

Yes. Seco is an adjective, and adjectives in Portuguese agree in gender and number with the noun they describe.

ar is masculine singular → o ar
So the adjective must be masculine singular → seco

Other forms would be:

ar seco (masc. sing.)
água seca (fem. sing., theoretical)
dias secos (masc. plural)
gargantas secas (fem. plural)

In your sentence:

o ar (masc. sing.) está seco (masc. sing.)

Is the comma after Quando o ar está seco required?

When a subordinate clause (like Quando o ar está seco) comes before the main clause, it is standard and stylistically preferred to put a comma:

Quando o ar está seco, sinto mais irritação na garganta.

If the quando clause comes after, the comma is usually omitted:

Sinto mais irritação na garganta quando o ar está seco.

So, in this word order, the comma is expected and natural.

Is this sentence specifically European Portuguese? Would Brazilians say it differently?

The sentence:

Quando o ar está seco, sinto mais irritação na garganta.

is perfectly correct in European Portuguese, and also fully understandable and natural in Brazilian Portuguese. It’s standard, neutral vocabulary.

Possible small differences you might hear in Brazil:

Some might say na minha garganta more often than Europeans, who are more likely to drop minha in expressions about body parts.
Pronunciation will differ (European vs Brazilian accent), but the grammar and wording are fine for both.

For learning Portuguese from Portugal, this sentence is completely appropriate and idiomatic.