Facts:Second hand smoke is dangerous, but poorly understood.
The primary concerns here are the PM or Particulate Matter. An aggregate level of PM over 35 for 8 hours will increase your risk of death by about 3% (Thats three years out of your a lotted 120). A further rise of +10 adds +3% (egg 45 - 6%, 55 - 9%). This includes A HUGE list of potential causes of death. (Primarily lung and heart, but almost every major organ is damaged through the process).
It is my estimate that smoking (I have never measured the values of cigarette smoke) can raise a 1 cubic meter area of space by upwards of 400. Keep in mind, most spaces are larger than that, and so the number drops exponentially. If the space is ventilated your risk to severe levels is minimized. Here's my working rule of thumb:
Smell - 75 to 150 range
Sight - maybe 200'ish, but probably 300+
Throat, nose, and ear are going to be your early warning. If you are finding your nose is plugged up more often, you should reduce your levels of exposure. If you start getting infections you should cut off all exposure. (Or the infections could (5-10%) damage your ears/nose/throat)
Wikipedia has a very useful article: (wiki:particulate matter)
The Mongolian government agency recorded a 45% increase in the rate of respiratory illness in the past five years
Not the reference I wanted, I remember somewhere on wiki there's a fifty percent rise in all major disease groups. Annual exposure is probably around 200.
My opinion: Wear a mask, if the money is really good, you should expend a fraction of the money now to ensure longer lasting good health later. Economically it's the prudent decision. Also it is far less confrontational a solution (I don't hesitate to confront smokers, but since you are here...), you will be asked why your wearing a mask, and you can explain. Also you wont need to sound demanding or pushy. NOTE: you probably will be teased about it.
google: 3m disposable respirators, shouldn't be too expensive and should be relatively available world wide.
Source:Living 3+ years in a highly polluted outdoor air quality environment. (I can drive to mongolia to get CLEANER air)
HVAC 500 level coursework in college, H. V. A. C - Heating,
Ventillation, and Air Conditioning
WHO, EPA, and WebMD all have excellent material available. If you want to study the topic further. I just gave you a quick summary IMO.