The presence of multiple smokers in outdoor settings is likely to increase exposure substantially from the single-smoker case. Our data can be used to estimate exposures for situations with multiple smokers. Since it is reasonable to assume that average smoke levels increase in proportion to the number of outdoor smokers, we can then roughly estimate levels of particle exposure for different distances from groups of smokers. A nonsmoker who is 1 or 2 feet away from a single burning cigarette, can easily inhale pollution that is 10 times greater, on average, than background "clean" levels, so that being 10+ feet away is required to avoid elevated average exposure during smoking. However, WITH MULTIPLE SMOKERS PRESENT, THE AVERAGE LEVELS COULD BE 20, 30, or 50+ TIMES GREATER THAN BACKGROUND AT CLOSE RANGE, SO THAT MOVING TO 20 TO 50+ FEET AWAY FROM THEM WOULD LIKELY BE REQUIRED TO AVOID EXPOSURE.