What was the purpose of this study?

We wanted to quantify the potential level of exposure to outdoor tobacco smoke that could occur in everyday outdoor locations. To do this, we visited parks, outdoor cafes, sidewalks, and outdoor pubs where smokers were present and we measured airborne levels of particle air pollution in real-time. The use of real-time measurements allowed us to directly match air pollution levels with observed smoking activity. We also performed controlled experiments, where we precisely examined the levels of air pollution at different distances from active cigarettes.

What are the main findings of the study?

Our main finding is that air pollution from outdoor tobacco smoke can be quite high near active smokers. The average levels can be comparable to those measured _indoors_ when people smoke. When one is within a few feet of an outdoor smoker and downwind, the levels are highest. An important finding was that a person near an outdoor smoker could breathe in wisps of smoke that could be 10s or 100s of times more concentrated than normal background air pollution levels.

Why is this research important? Who will use the results?

The results of our study are important to the public, who may wish to understand the level of their exposure near outdoor smokers, and to policy makers, who are considering bans on outdoor smoking in different locations. Knowledge of the levels of air pollution caused by smoking can solidify the hazardous nature of outdoor smoking in people's minds and help them to understand its potential risks.

Why is this research new?

Our study is the first to be published in a scientific journal on the levels of outdoor air pollution that can occur near active outdoor smokers. Previously, the exact level of air pollution that could occur outdoors from smoking under various circumstances of proximity and wind was unknown. Our study is also unique in that we have used, tested, and calibrated 5 different kinds of instruments to measure real-time outdoor air pollution levels. These instruments allowed us to characterize peak pollution levels on a second-by-second or minute-by-minute basis.

Why did you measure particulate matter?

Tobacco smoke consists of small particles suspended in the air. The tobacco smoke particles contain a large number of different kinds of chemicals. By measuring the entire mixture of chemicals in particulate matter, we can assess the overall level of air pollution resulting from smoking. Also, since particle measurement is a standard practice in air pollution assessment for the USEPA and others, using particles allows us to place the degree of air pollution generated by the smoking of one or more cigarettes into a larger context of different types of pollution sources. For example, the current USEPA standard for daily average levels of outdoor air particulate pollution is 35 micrograms per cubic meter of air. We measured average particle levels for a 10-minute cigarette of as much as 200 or 300 micrograms per cubic meter of air.

Are levels really the same as for indoor smoking?

Yes, under some conditions. When measured close to a person who is actively smoking, air pollution can reach very high levels that are similar to levels observed for indoor smoking. However, the difference for outdoor air is that pollution levels disappear rapidly when a smoker stops smoking, whereas indoors they can persist for several hours.

Are your results relevant to other cities and towns?

Yes. We observed air pollution levels concurrently with the direct observation of active smoking at different smoker distances and wind speeds. Therefore, our results are generalizable to many other outdoor situations where people smoke. Our results can be used to reliably understand potential exposures to outdoor tobacco smoke pollution in typical locations in any city locale where people tend to congregate -- including parks, sidewalks, restaurants, etc. People in cities and towns around the world can benefit from the findings of our study.

Aren't campfires and barbeques also polluting?

Some have argued that exposure to toxic chemicals can result from being near campfires or barbeques (outdoor grilling) -- in addition to from cigarettes -- but that no one is talking about banning these sources. This argument is a red herring and irrelevant to the consideration of smoking bans. Other sources should be considered independently from tobacco. In fact, we are unaware of the ability of people to indiscriminately burn campfires or have BBQs at cafes and on city sidewalks. But they can currently generate similar kinds of air pollution in many locations by smoking a cigarette or cigar. If people do not want to be exposed to the substantial air pollution caused by outdoor smoking in places they visit, then they are justified in pushing for smoking bans.

Don't smokers have a right to smoke somewhere?

We are not aware of any claim of a natural right for a person to generate toxic air pollution in the breathing space of others, especially when the pollution-generating activities are for recreational purposes only. Our research indicates that smoking outdoors can produce high levels of hazardous air pollution exposure for nearby people.

How can people avoid exposure to outdoor tobacco smoke?

The easiest way to avoid exposure to outdoor tobacco smoke air pollution is to be located a reasonable distance away from active smokers. For a single smoker, this distance is approximately 2 meters (6 feet) or more. However if one is directly downwind from a smoker for a significant time period, the distance will likely have to be greater to avoid exposure. We detected air pollution as far away as 9 to 12 feet from a single smoker. In addition, if there are multiple smokers, the distance will have to be increased; for example, if there are two or three active smokers present, moving to 6 or more meters (about 20 ft) away from the group may be necessary.

How do particles affect your health?

The small particles in tobacco smoke, together with their toxic and carcinogenic constituents, can penetrate deep into the human lung. Small particles in ambient air have been associated in previous studies with increased morbidity and mortality, especially for sensitive populations, such as the elderly or those with existing respiratory disease. Since tobacco smoke particles are especially toxic, they are likely to carry an even greater risk than the same level of ambient air pollution.

How will this study impact smoking bans?

If people realize that being near outdoor smokers can result in potentially large exposures to toxic air pollution, they may decide they do not wish to be exposed in a variety of outdoor settings. This realization may lead to an increased number of smoking bans in public locations.

Is outdoor tobacco smoke really toxic?

Yes. Tobacco smoke contains over one hundred recognized toxic chemicals, hazardous air pollutants, or known carcinogens -- including benzene, arsenic, hydrogen cyanide, cadmium, 1,3-butadiene, and benzo-a-pyrene. In addition to being a strong irritant and potential annoyance, tobacco smoke can have adverse effects on the human respiratory and cardiovascular systems.

Is there really a health basis for outdoor smoking bans?

Yes. Concentrated streams of outdoor tobacco smoke can, at the very least, act as a respiratory or eye irritant. But outdoor tobacco smoke may also pose a serious health hazard for severe asthmatics even if the exposure is transient, since tobacco smoke may act as a trigger. Those with compromised cardiovascular systems may be at risk from even brief exposures. People spending time near outdoor smokers over multiple hours, such as waiters or dinner guests, can receive exposure that exceeds the current USEPA limit on fine particulate matter pollution. Hence, outdoor tobacco smoke is a real occupational and hospitality health issue, and there is a compelling basis to institute smoking bans to protect individuals in both commercial and non-commercial settings.

Isn't air pollution from vehicles and power plants more serious?

Some critics try to diminish the impact of outdoor air pollution from smoking by saying that air pollution from other combustion sources (for example, cars, trucks, and power plants) is much worse. This argument is flawed.

In fact, when no smokers were present, we consistently measured background air pollution levels that were practically zero. We found the air in typical urban locations in California, even near roadways, to be generally quite clean compared to air in the vicinity of smokers.

It is important to remember that one's proximity to a source of air pollution is most important. Unless you are standing near a smokestack or right at a tailpipe, the air pollution from cars and power plants mixes in the atmosphere and becomes very diluted before it reaches your lungs. In contrast, a cigarette, while it has much smaller emissions than a power plant or car, is more likely to be very close to people and, therefore, to expose them to concentrated levels.

To put things in perspective, we typically measured background air pollution (from all distant sources) to be less than 10 or 20 micrograms per cubic meter of air. In contrast, we sometimes measured air pollution near a cigarette to be over 1000 micrograms.

What health effects result from exposure to tobacco smoke?

Since outdoor air pollution from smoking can reach high levels for short time periods, there is the potential for acute health effects. Minor health effects include eye and respiratory irritation. Previous research has shown that even short exposures to air pollutants in cigarette smoke can be seriously harmful to children and adults, potentially leading to an increased likelihood of ear and respiratory infections, the onset or increased severity of asthma attacks, and a possible increased risk of myocardial infarction for those who already have some cardiovascular risk.

What is the benefit of real-time monitoring?

We used five different types of real-time airborne particle monitors in our outdoor study of tobacco smoke. With these instruments, we were able to measure air pollution every few seconds or minutes, and, therefore, to pinpoint the high peak levels of air pollution that could occur. Another benefit of these instruments was the ability to correlate pollution levels directly with the presence of active cigarettes. An important feature of most of the instruments was their small size and portability. They are kind of like having a "laboratory in a lunch box". These small particle monitors are a major technical leap from the old pump-with-filter way of making particle measurements, which requires collecting material on a filter and weighing it later in a formal lab facility.

What is the proximity effect?

Previous research has found that exposure to indoor air pollution becomes elevated when one is close to the source of pollution. This phenomenon has been called the "proximity effect". We observed the same effect in our study of outdoor air pollution near smokers, with high levels occurring near active smoking and low levels occurring further away (beyond about 2 meters, or 6 feet, from a single smoker). Note that the more smokers present, the further away you would likely have to be to avoid any exposure.

Which people are most at risk for outdoor smoke exposure?

Anyone who spends a significant amount of time close to one or more outdoor smokers could be at risk for sizable exposure. For example, servers at outdoor restaurants and pubs where smoking is allowed could be exposed repeatedly to high air pollution levels as they approach tables containing active smokers. Also, children who accompany smoking parents or guardians could also receive substantial amounts of exposure during the course of a day.