Learn Hardcore Greek: Τα καυσαέρια από τα αυτοκίνητα κάνουν τον αέρα βρώμικο. - The exhaust fumes from the cars make the air dirty.

In older or more formal Greek, neuter plural subjects can sometimes take a singular verb (e.g. τα παιδιά παίζει), but in modern standard spoken Greek the normal form is plural: τα καυσαέρια κάνουν.

What is the grammatical gender, number, and case of τα καυσαέρια and τα αυτοκίνητα?

Both are:

τα – definite article, neuter, plural, nominative (for the subject) or accusative (for objects)
καυσαέρια – noun, neuter, plural, nominative (here: subject of the verb)
αυτοκίνητα – noun, neuter, plural, accusative (object of the preposition από)

So:

Τα καυσαέρια is the subject (nominative plural neuter).
από τα αυτοκίνητα is a prepositional phrase; τα αυτοκίνητα is in the accusative plural neuter because από takes the accusative.

Why is it τον αέρα and not ο αέρας?

Because αέρας is the direct object of the verb κάνουν.

ο αέρας – nominative (subject form): the air as the doer of the action.
τον αέρα – accusative (object form): the air as the thing affected by the action.

Here, Τα καυσαέρια (subject) κάνουν (make) τον αέρα (object) βρώμικο (dirty).
So we must use the accusative: τον αέρα.

Why is the adjective βρώμικο in that form, and how does it agree with τον αέρα?

The adjective βρώμικος, -η, -ο (dirty) has:

Masculine: βρώμικος (nom. sg.), βρώμικο (acc. sg.)
Feminine: βρώμικη (nom./acc. sg.)
Neuter: βρώμικο (nom./acc. sg.)

αέρας is masculine, singular, accusative (τον αέρα).
The masculine singular accusative form of the adjective is βρώμικο, so:

τον αέρα βρώμικο = the air (masc. acc.) + dirty (masc. acc.)

So βρώμικο is masculine here, agreeing with αέρα, even though it looks the same as the neuter form.

Can we put βρώμικο before αέρα? For example, say Κάνουν τον βρώμικο αέρα?

You can change the word order, but the meaning changes slightly:

κάνουν τον αέρα βρώμικο – they make the air dirty (action + resulting state)
κάνουν τον βρώμικο αέρα – sounds like they make the dirty air as an object (awkward and not natural here)

Natural alternatives:

Τα καυσαέρια από τα αυτοκίνητα κάνουν τον αέρα βρώμικο. (most common)
Τα καυσαέρια από τα αυτοκίνητα κάνουν τον αέρα πολύ βρώμικο. (they make the air very dirty)
Τα καυσαέρια από τα αυτοκίνητα κάνουν τον αέρα βρώμικο και ανθυγιεινό.

Placing βρώμικο before αέρα normally describes a pre-existing dirty air (ο βρώμικος αέρας = the dirty air), not air that becomes dirty through the action.

What is the pattern with κάνω here? How do I know to use κάνουν τον αέρα βρώμικο?

The structure is:

κάνω + [object in accusative] + [adjective]
= to make something (become) [adjective]

Examples:

Κάνουν τον αέρα βρώμικο. – They make the air dirty.
Αυτό κάνει τη ζωή δύσκολη. – This makes life difficult.
Η ζέστη κάνει το δωμάτιο αποπνικτικό. – The heat makes the room stifling.

So:

τον αέρα – direct object (what is affected)
βρώμικο – resulting state (adjective)

Why is the preposition από used? Could I use something like a genitive instead?

από is a very common preposition meaning:

from (origin/source)
by (agent: who/what causes something)
out of, since, because of (in some contexts)

In this sentence, από shows the source or cause:

καυσαέρια από τα αυτοκίνητα = exhaust fumes from cars / caused by cars.

You could also say:

Τα καυσαέρια των αυτοκινήτων κάνουν τον αέρα βρώμικο.

This uses a genitive (των αυτοκινήτων = “of the cars”). It sounds a bit more formal or written; από τα αυτοκίνητα is more neutral and very common in speech.

Why is it από τα αυτοκίνητα and not από αυτοκίνητα? Is the article τα necessary?

Both are possible, with a nuance:

από τα αυτοκίνητα – from the cars (general class, but presented as a known category; quite normal and idiomatic)
από αυτοκίνητα – from cars (more indefinite, like “from (some) cars in general”)

Greek tends to use the definite article more often than English in generic statements. So:

Τα καυσαέρια από τα αυτοκίνητα κάνουν τον αέρα βρώμικο.
feels like a generic statement about car exhaust in general; this is the most natural version.

από αυτοκίνητα is grammatically correct but sounds slightly more like “from cars (as opposed to something else)” and is less typical in a neutral general statement.

What is the singular of καυσαέρια, and is it actually used?

Singular: το καυσαέριο – exhaust fume / exhaust gas
Plural: τα καυσαέρια – exhaust fumes

In practice, you almost always hear the plural τα καυσαέρια, even when talking about exhaust in general. The singular το καυσαέριο does exist but is less common in everyday speech; it may appear more in technical or scientific contexts.

Is καυσαέρια countable, or is it more like “air” or “water” in English?

Grammatically, it’s a normal countable noun (neuter plural). You can say:

πολλά καυσαέρια – a lot of exhaust fumes
λίγα καυσαέρια – few exhaust fumes

Conceptually, though, it often refers to exhaust as a mass (like “smoke” or “pollution” in English) rather than individual “units” of exhaust. So it behaves like a countable noun in grammar, but often like a mass noun in meaning.

How do you pronounce αυτοκίνητα and καυσαέρια, especially the αυ combinations?

Stress marks show which syllable is stressed:

αυτοκίνητα – α υ το κ ί ν η τα → αυτοκίνητα: [aftoˈcinit̪a]
- αυ before a consonant like τ is pronounced [af]
- So: αυ- sounds like af-
καυσαέρια – κα υ σ α έ ρ ι α → καυσαέρια: [kafsaˈeria]
- καυ before σ is [kaf]
- The stress is on -αέ-: καυ-σα-Ε-ρι-α

So roughly:

αυτοκίνητα ≈ af-to-KEE-ni-ta
καυσαέρια ≈ kaf-sa-ER-i-a

Is βρώμικο the only correct spelling, or can it also be written βρόμικο?

Both spellings exist:

βρώμικος / βρώμικο – more common nowadays and considered the standard spelling in many contexts.
βρόμικος / βρόμικο – also seen; some speakers and dictionaries accept it as an alternative.

Pronunciation is the same ([ˈvromikos]). For learning purposes, stick with βρώμικο; you will understand βρόμικο if you see it.