Journal Article 1)
The current lack of empirical data on outdoor tobacco smoke (OTS) levels impedes OTS exposure and risk assessments. We sought to measure peak and time-averaged OTS concentrations in common outdoor settings near smokers and to explore the determinants of time-varying OTS levels, including the effects of source proximity and wind. Using five types of real-time airborne particle monitoring devices, we obtained more than 8000 min worth of continuous monitoring data, during which there were measurable OTS levels.
Measurement intervals ranged from 2 sec to 1 min for the different instruments. We monitored OTS levels during 15 on-site visits to 10 outdoor public places where active cigar and cigarette smokers were present, including parks, sidewalk cafés, and restaurant and pub patios. For three of the visits and during 4 additional days of monitoring outdoors and indoors at a private residence, we controlled smoking activity at precise distances from monitored positions.
The overall average OTS respirable particle concentration for the surveys of public places during smoking was approximately 30 μg m−3. OTS exhibited sharp spikes in particle mass concentration during smoking that sometimes exceeded 1000 μg m−3 at distances within 0.5 m of the source. Some average concentrations over the duration of a cigarette and within 0.5 m exceeded 200 μg m−3, with some average downwind levels exceeding 500 μg m−3. OTS levels in a constant upwind direction from an active cigarette source were nearly zero. OTS levels also approached zero at distances greater than approximately 2 m from a single cigarette. During periods of active smoking, peak and average OTS levels near smokers rivaled indoor tobacco smoke concentrations. However, OTS levels dropped almost instantly after smoking activity ceased. Based on our results, it is possible for OTS to present a nuisance or hazard under certain conditions of wind and smoker proximity.
This article is the first peer-reviewed publication of systematic measurements of OTS concentrations. The main conclusion from these data, that OTS levels can be substantial under certain conditions, is vital to the development of outdoor tobacco control policy. Because adequate information on OTS levels and human exposures has previously been lacking, the estimation of health risks associated with OTS has been hindered, and public discourse concerning OTS has been impaired. The present study also has shown that continuous, portable airborne particle monitors are suitable in OTS investigations across a range of locations and environmental conditions.
The measurement of OTS is a new area in terms of epidemiologic and human exposure investigations. The present work provides some of the first evidence that OTS levels can be substantial under certain conditions of wind and proximity. The major findings of our research are summarized below.
First, real-time particle instruments, especially those based on light scattering, are useful in characterizing the determinants of OTS levels, which fluctuate on a time scale of seconds. The different particle detection instruments provide consistent findings and support the general conclusion that significant OTS levels can occur near smokers.
Second, outdoor particle concentrations measured close to a cigar or cigarette exhibit multiple concentration spikes, or microplumes, which are similar to those that have been observed close to indoor particle sources.
Third, average OTS particle levels near active sources over the course of one or more cigarettes can be comparable with average well-mixed indoor SHS particle levels observed to occur in living rooms or bedrooms during smoking. Average OTS particle concentrations can reach hundreds of micrograms per meter cubed. Unlike indoor SHS levels, which decay slowly over a period of hours, OTS levels drop abruptly to zero when smoking ends.
Fourth, OTS levels are highly dependent on wind conditions. Upwind levels are likely to be very low, whereas downwind OTS levels during periods of active smoking can be very large with 10-second peak levels at the closest positions potentially exceeding 1500 µg m¯³ and average levels over the duration of a single cigarette potentially exceeding 500 µg m¯³.
Fifth, OTS levels are highly dependent on source proximity. Levels at 0.25– 0.5 m can drop by half or more as the distance increases to 1–2 m. At distances >2 m, levels near single cigarettes were generally close to background. The concentrations at different distances are influenced by wind conditions. We found that it was possible for there to be detectable OTS levels at downwind positions of ≥4 m from a single active cigarette. Also, as the number of active cigarettes increases, the distance at which OTS is detectable is likely to increase.
Sixth, in outdoor restaurant patios and parks, where there may be multiple smokers, between 8 and 20 cigarettes smoked sequentially could cause an incremental 24-hr particle exposure greater than a threshold level of 35µg m¯³ for a person who is within 0.5 m of the smokers. This threshold level is the 24-hr EPA health-based standard for fine particles.
Our results demonstrate that OTS can be high during periods of smoking in locations where persons are near active smokers. Therefore, it is possible for OTS to present a nuisance or hazard under certain conditions.
Examples of scenarios where OTS levels might be high include eating dinner with a smoker on an outdoor patio, sitting at a table next to a smoker at a sidewalk café, sitting next to a smoker on a park bench, or standing near a smoker outside a building. Children who accompany a smoking parent or guardian may experience substantial exposure. Outdoor restaurant or pub workers who spend a significant portion of their time within a few feet of active smokers are also likely to receive relatively large total OTS exposures over the course of a day, possibly exceeding the EPA 24-hr health standard for fine particles. If one is upwind from a smoker, levels most likely will be negligible. However, if the smoker’s position changes or one spends time downwind from a smoker, then moving to a distance of >2 m can reduce the likelihood of experiencing elevated particle exposure because of OTS. Future studies should measure OTS levels for dynamic situations with multiple smokers, including continuous measurements of personal OTS concentrations or biomarker levels for workers in outdoor locations.
Support for health-based OTS bans may lie in a potential acute effect on susceptible populations. Short-term OTS exposures might be life threatening for high-risk persons, because the human cardiovascular system is very sensitive to secondhand smoke.31 A recent before-and-after smoking ban study showed a decreased chance of myocardial infarction when a ban was in place,32 which suggests that there is an acute risk associated with SHS exposure for persons at increased risk of coronary heart disease or with known coronary artery disease. 33
31 Barnoya, J.; Glantz, S. Cardiovascular Effects of Secondhand Smoke: Nearly as Large as Smoking; Circulation 2005, 111, 2684-2698.
32 Sargent, R.P.; Shepard, R.M.; Glantz, S.A. Reduced Incidence of Admissions for Myocardial Infarction Associated with Public Smoking Ban: Before and after Study; BMJ 2004, 328, 977-980.
32 Pechacek, T.F.; Babb, S. How Acute and Reversible Are the Cardiovascular Risks of Secondhand Smoke; BMJ 2004, 328, 980-983.