Hi J. -
You have several problems here. One is the smoking, obviously, but it's not just a question of your child being exposed to the smoke while it's happening - it's the fact that the smoke never really clears from your ex-husband's apartment and your child is exposed to the toxins even if the cigarette was smoked an hour or 3 hours ago. The second problem is that, if you bring up the girlfriend's smoking, it will be perceived as an objection overall to the girlfriend - either by him, or by her, or by both. So if you discuss it, you have to be very clear and calm about what your concern is. You can get lawyers involved, but that costs money and I can tell you, I have been through years of legal nonsense with my husband's ex-wife, and it's draining. Now that the weather is getting nice, maybe your ex can spend a lot of time outdoors with your daughter - parks and playgrounds, etc. If you approach it like you are accepting of his right to see a woman, but you'd like the smoking to be outdoors, it will be less threatening to them. It's likely that the 19 year old will get awfully tired of a 2 year old cramping her style, and she will not want a toddler there to impose on her Saturday night fun. Right now, she's probably around a lot just to stick it to you, and your ex may be encouraging it to show you that he is desirable and popular. He also may want the help with your child - I don't know how hands-on he is as a dad.
The third issue, of course, is attachment - but this is something beyond your control. It would be nice if he didn't introduce a new woman into your daughter's life at this early stage, but it doesn't look like that's going to happen. If your daughter is not staying overnight at his apartment, there is less chance for a strong bond to develop. As long as he is not neglecting your daughter in any way, it will be okay. The more you protest, the more likely he may be to cling to this relationship - it depends on his issues, and whatever animosity is between you and him. As much as you can take the high road, the better it will be - hard, I know. If you can say, "Did you have fun with Daddy and Susie?" in a chipper voice, it will make it easier to say to him, "I think it's nice that Susie is devoting so much time to our daughter. A child can't have too much affection. I hope you agree with me, though, that the smoking should be confined to the outdoors, for our daughter's welfare." See if that works. Good luck!!