Emisja spalin jest wysoka.

Emisja is a noun meaning emission. In this sentence, emisja spalin means exhaust emissions or the emission of exhaust gases.

Yes, it is very close to English emission, but in Polish it is often used in specific contexts like:

• emisja spalin — exhaust emissions
• emisja CO2 — CO2 emissions
• emisja gazów cieplarnianych — greenhouse gas emissions

Because spalin is the genitive plural form of spaliny.

The basic form is:

• spaliny — exhaust fumes / exhaust gases

After a noun like emisja (emission), Polish often uses the genitive to show emission of what? So:

• emisja spalin = emission of exhaust gases

This is a very common pattern in Polish:

• produkcja samochodów — production of cars
• analiza danych — analysis of data
• zużycie energii — consumption of energy

Jest is the 3rd person singular form of być (to be) and means is.

So:

• Emisja spalin jest wysoka. = Exhaust emissions are high.

In Polish, the verb to be in the present tense is usually not omitted in sentences like this. So you normally need jest here.

You would not usually say:

• Emisja spalin wysoka.

That sounds incomplete in standard Polish.

Because it agrees with emisja, which is a feminine singular noun.

Polish adjectives must agree with the noun in:

• gender
• number
• case

Here:

• emisja — feminine singular nominative
• wysoka — feminine singular nominative

Compare:

• Emisja jest wysoka. — The emission is high.
• Poziom jest wysoki. — The level is high. (poziom is masculine)
• Zużycie jest wysokie. — The consumption is high. (zużycie is neuter)

The dictionary form is wysoki, meaning high.

The forms change depending on gender:

• wysoki — masculine
• wysoka — feminine
• wysokie — neuter

So in this sentence, wysoka is used because it describes emisja.

Sometimes, but wysoka is the more natural choice here.

In Polish, wysoki is often used with abstract measurable things such as:

• wysoka temperatura — high temperature
• wysoka cena — high price
• wysokie ryzyko — high risk
• wysoka emisja — high emission

Duża means big/large, and although it can sometimes work, it is less standard here. A Polish speaker would usually prefer:

• Emisja spalin jest wysoka.

Polish often uses a singular noun where English prefers a plural one.

So:

• Emisja spalin jest wysoka. literally: The emission of exhaust gases is high but in natural English this may be translated as:
• Exhaust emissions are high.

This is a translation difference, not a grammar mistake. Polish is focusing on the emission as one phenomenon.

Emisja is in the nominative singular because it is the subject of the sentence.

The structure is:

• Emisja spalin — the subject
• jest — the verb
• wysoka — the predicate adjective describing the subject

So emisja stays in the nominative, while spalin is in the genitive because it depends on emisja.

Yes, Polish word order is fairly flexible, but the neutral, standard order is:

• Emisja spalin jest wysoka.

Other orders are possible, for example:

• Wysoka jest emisja spalin.
• Jest wysoka emisja spalin.

But these can sound more marked, literary, or focused in a different way. For a learner, the basic version is the safest and most natural.

A rough guide for an English speaker:

• Emisja ≈ eh-MEE-sya
• spalin ≈ SPAH-leen
• jest ≈ yest
• wysoka ≈ vih-SO-ka

A few useful notes:

• j in Polish sounds like English y
• sj in emisja gives a soft sh/y-like sound, roughly sya
• y in wysoka is not exactly English i; it is a harder vowel

It sounds fairly neutral, but somewhat technical or environmental/official because of the phrase emisja spalin.

You might see it in:

• reports
• regulations
• discussions about cars or pollution
• environmental texts

In very everyday speech, people might also say things like:

• Ten samochód ma wysoką emisję spalin. — This car has high exhaust emissions.
• To auto dużo spala. — This car uses a lot of fuel / burns a lot.

Yes, you would be understood, but it is less idiomatic than wysoka.

Polish often prefers certain adjective-noun combinations, and wysoka emisja is one of the standard ones. So if you want to sound natural, use:

• Emisja spalin jest wysoka.

Yes, a few very useful ones:

• niska emisja — low emission
• Emisja spalin jest niska. — Exhaust emissions are low.
• wysoka emisja spalin — high exhaust emissions
• ograniczyć emisję spalin — to reduce exhaust emissions
• poziom emisji spalin — the level of exhaust emissions

Notice another case change here:

• emisja — nominative
• emisję — accusative, as in ograniczyć emisję (reduce the emission)