I'm not going to get into the whole smoking aspect of this argument. We all know it's bad.
I would never leave my child inside playing while I went outside. She would have a total panick attack, if she could see me out there, and if I left her alone where she couldn't see me, anything could happen. My house is very babyproofed, but I know that in a few seconds, she could easily learn to climb a piece of furniture, or get her fingers slammed in a door.
That said I have left her on occasion, when she's fast asleep, to go in the backyard and do "dog-duty." It has to be done when she's asleep, because if she were awake, she'd want to come outside and play in it. :P My yard is very tiny, so I'm not far from her at all (I'm actually further away from her if I go to the basement to do laundry while she naps), and have the baby monitor with me so I can hear anything that's happening in her room. She still sleeps in a crib, so I know she can't climb out and get into trouble.
As for the smoking (ok, I lied and am going to say something about it after all), do you have close neighbours? I commend you for smoking outside at least, for your child's sake.....but my neighbours smoke outside for the same reason. While they're working to keep their kids safe, what they don't realize is that their second hand smoke is filling my daughter's bedroom, and the rest of my home. My husband worked very hard to quit smoking a few years ago, so that we would have a smoke free home, but my house still smells like cigarettes thanks to these aweful neighbours. I've asked them to stop, but for their children's sake, they refuse to smoke inside. They'd rather poison my child.
I have to keep all of my windows and doors shut, which is horrible because the air gets so stuffy and stale.
Just my semi-off-topic rant. :P