And, as is tradition, confetti and fireworks will help continue the celebration after midnight, according to the Times Square Alliance.

What part of speech is as?

Is it a pronoun?

If so, what does this pronoun refer to?

It seems to have aspects of several different parts of speech, doesn't it? It's listed at www.m-w.com as adverb, conjunction, pronoun, and preposition! I'm leaning toward conjunction or pronoun.

It may be thought of as a conjunction because it joins a subordinate clause (with inverted subject and verb) to the main clause.

It may also be thought of as a pronoun (like the relative pronoun which used non-restrictively).

Confetti and fireworks will help ... midnight, which/as is tradition.

If it's a pronoun, the reference is to the idea of the entire sentence, that is, to the fact that confetti and fireworks will .... or to the use of confetti and fireworks to help continue .... This is the same (admittedly vague) reference that which would have, if which were substituted for as. (But which can't substitute for as in that sentence-initial position. It can only substitute if moved, as I have done in my example above.)

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Understand perfectly!
Thanks so much, CJ.
It does not destroy nature as is often the case with other means of producing food.

Does it mean 'other means of producing food do not destroy nature, either' or 'other means of producing food destroy nature."?

I think the former is correct.
Emotion: big smile
This is one of those! "What is the scope of the negation?" we ask ourselves! These sometimes stump even us native speakers.

Generally speaking, the not in the main clause is not included in the meaning of the as is the case clause. And that's what's happening here. So it means

It does not destroy nature -- although other means of producing food often DO destroy nature.

At least, that's what I surmise, not knowing what preceded. The sentence or two that leads up to this kind of sentence is often needed to get the full picture.

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Many thanks, CJ.