Should the questioner tell his smoker friend, who is not committed to prayer, about a study opportunity at one of Makkah's universities, bearing in mind that it might help him repent, or it might contribute to polluting Makkah's air, and others might follow his example?

First, you should advise your friend to preserve his prayers and quit smoking. If he does not benefit from this advice, then abandon him as a disciplinary measure. If abandonment does not work, then there is no good for you in his companionship, so distance yourself from him.

As for informing him about the university's location, you should consider what is most likely his current state: If his repentance and reformation are probable, then inform him as a form of دعوت and advice. If, however, you suspect the opposite, then there is no need to inform him.

If you are compelled to study in a mixed-gender university, then fear Allah, and protect your faith by lowering your gaze, avoiding places of temptation, seeking righteous companions, trying to get married if possible, and frequently remembering Allah and supplicating Him for steadfastness.