You'll have trouble finding many people to study. From the evidence I've seen, intensity of smoke exposure is much more problematic than volume. Light smokers

You'll have trouble finding many people to study. From the evidence I've seen, intensity of smoke exposure is much more problematic than volume. Light smokers still have 5-10x the chance of developing lung cancer than a non-smoker. That might be a good first estimate for smokers who only smoke one month out of the year.