Røgudviklingen er stor.

It is a compound noun:

• røg = smoke
• udvikling = development
• -en = the definite ending

So røgudviklingen is literally the smoke development.

In Danish, compound nouns are very common, and the last part is the “main” noun. Here, the main noun is udvikling, so that determines the gender and ending of the whole compound.

Because Danish often puts the at the end of the noun instead of using a separate word before it.

So:

• en udvikling = a development
• udviklingen = the development

And with the compound:

• en røgudvikling = a smoke development / smoke formation
• røgudviklingen = the smoke development

This is one of the big differences from English.

Er is the present tense of at være = to be.

So this is just the normal present-tense linking verb:

• Røgudviklingen er stor.
• literally: The smoke development is large.

Danish uses er in the same kind of way English uses is.

Because stor agrees with the noun’s gender and use here.

The noun røgudvikling is common gender (it takes en, not et), so in the singular the adjective is:

• en stor røgudvikling

Not:

• et stort røgudvikling ❌

Also, in this sentence the adjective is predicative—it comes after er—so it stays in the basic agreement form:

• Røgudviklingen er stor.

Compare:

• en stor røgudvikling = an indefinite noun phrase
• røgudviklingen er stor = after er
• den store røgudvikling = definite noun phrase before the noun

That last contrast is very important: after er, Danish does not use the definite adjective form just because the noun is definite.

Because Danish treats adjectives differently depending on where they are.

Before a definite noun, you usually get the definite/plural form:

• den store røgudvikling

But after er, the adjective is a predicate adjective, and then you do not use the definite form just because the noun is definite:

• Røgudviklingen er stor.

So:

• den store røgudvikling ✅
• røgudviklingen er stor ✅
• røgudviklingen er store ❌

This is a very common learner question.

This is standard Danish main-clause word order:

• Røgudviklingen = subject
• er = verb
• stor = subject complement

So the pattern is:

Subject + verb + complement

That is the most basic and natural order here.

If you turn it into a yes/no question, the verb comes first:

• Er røgudviklingen stor?

Yes, and that is often a very natural alternative.

Compare:

• Røgudviklingen er stor.
  Focuses on the smoke development as the subject.

• Der er stor røgudvikling.
  Means something like There is heavy/significant smoke development and often sounds a bit more idiomatic in reports or descriptions.

Both are good Danish, but they are structured differently.

Yes. In Danish, stor can mean more than physically big. It can also mean:

• great
• extensive
• significant
• heavy

So here stor describes the extent/intensity of the smoke development, not necessarily size in a simple physical sense.

That is why it works naturally in formal or descriptive language.

For an English speaker, the hardest part is ø.

A helpful rough guide:

• ø is somewhat like the vowel in English bird, but with rounded lips
• the final g in røg is not a hard English g sound

So røg is not pronounced like rog or rug.

You can think of it as a short, rounded vowel plus a soft ending. If you are learning pronunciation, ø is one of the key Danish vowels to practice separately.

Yes. It is one compound noun, so it is pronounced as one word, not as separate words.

Danish compounds are written together:

• røgudvikling
• brandalarm
• togstation

The main stress usually falls early in the compound, so in røgudviklingen, the first part gets important stress.

It is common gender, which is why you say:

• en røgudvikling
• røgudviklingen

You often have to learn noun gender together with the noun. In a compound, the gender usually comes from the final element, and here the final element is udvikling, which is common gender.

So if you know:

• en udvikling

then you can also know:

• en røgudvikling

Normally, that would not sound right in standard Danish.

You would usually say either:

• Røgudviklingen er stor.
  if you mean a specific smoke development

or:

• Der er stor røgudvikling.
  if you are making a more general statement

Bare singular nouns without an article or definite ending are much more limited in Danish than in English. So English speakers often try to leave out the article when Danish would not.

Yes, it sounds fairly formal or technical. You might see it in:

• safety notices
• fire reports
• emergency instructions
• official descriptions

In everyday speech, people might choose other wording depending on context, but this sentence is perfectly normal Danish. It just has a slightly formal/report-like tone.