This is a very important topic of research. Despite the well-known risks, about 1 in 5 Americans still smoke.
You mentioned an interest in secondhand smoke, you might also be interested in a newly-defined concept of "third hand smoke":
http://www.nytimes.com/2009/01/03/healt ... smoke.html
Since you mentioned wanting to build something with your hands--I wonder if it's possible to build/develop some sort of device that detects the toxins from smoke? Then you could look into, for example, what toxins are present while someone's in a room smoking, and different times after they leave?
I'm afraid how to measure the toxins puts me a little out of my depth...maybe other experts could chime in here? Here's a blog I found that links to a study it says has info on ways to measure cigarette toxins:
http://tobaccoanalysis.blogspot.com/200 ... ce_13.html or I wonder if there's a simple way to measure particles in the atmosphere?
You could even expand the study and go out into your environment to look at particle/toxin levels--eg compare the smoking and nonsmoking sections of a restaurant (if your town has such sections), and then different parts of the nonsmoking section closer or further from the smokers?
If you want to do something on the human body--keep in mind there are regulations about using people for science projects--maybe you could measure blood pressure or heart rate during, right after, and several hours after having a cigarette? Or compare body reaction to a cigarette to reaction to something like nicotine gum--if you want to encourage your subjects to quit.
I'm just throwing a couple ideas out there, I'm sure your brainstorming can come up with more. Good for you for getting a head start!