An adverb clause is a dependent clause that modifies the verb in the sentence and acts as an adverb in the sentence. Moreover, adverb clauses are identifiable by the use of time adverbs such as when, where, why, how, etc.
In the given sentence, the phrase bolded is <u>"when we arrived home"</u>. This phrase/ clause adds detail to the whole sentence while linking it to the main clause by "when".
Thus, the bolded clause functions as an adverb clause.
