Does a divorce vow take effect if the wife, who smokes cigarettes, puts the cigarette in her nose instead of her mouth, after her husband swore to divorce her if she put it in her mouth? And is the wife considered divorced despite her ignorance of the religious ruling at the time? And does expiation for the oath after several years permit the couple to reconcile?

If a man conditions his wife's divorce on an action, then she is divorced upon the performance of that action, according to the majority of scholars. As for your question, your act of smoking without putting the cigarette in your mouth would trigger the divorce. However, since you did this interpreting the oath to mean the literal wording, the preponderant opinion is that the divorce does not occur in this instance. As for the time you put the cigarette in your mouth, you have performed the sworn-upon act. Therefore, according to the opinion of the majority, the divorce has occurred. However, if your husband consulted trustworthy scholars and they issued a fatwa (definition) that the divorce did not occur and that an expiation for the oath is due, then there is no harm in that. You must repent to Allah by quitting smoking and regretting what has passed.