Are outdoor smoking bans scientifically justified?
Are outdoor smoking bans scientifically justified?
Science, technology, and life.
Sept. 17 2009 10:30 AM

Secondhand Smokescreen

Are outdoor smoking bans scientifically justified?

Smoking outside. Click image to expand.
Smokers in New York

Do studies of secondhand smoke justify bans on outdoor smoking?

William Saletan William Saletan

Will Saletan writes about politics, science, technology, and other stuff for Slate. He’s the author of Bearing Right.

In response to Tuesday's article about the crackdown in New York, many of you made good arguments for and against  the proposed restrictions. The best post came from James Repace, a biophysicist and former EPA staff scientist who does actual research on secondhand smoke. He's offering what we need much more of on the Internet: facts.

In Slate's Fray, Repace says I'm wrong about outdoor smoke:

Mr. Saletan states in part: "Studies have proved that secondhand smoke is harmful. But those studies aren't conducted in wide-open spaces." Sorry, Mr. Saletan, you have not done your homework. The State of California's Air Resources Board (ARB) that regulates California's outdoor air did a massive report in 2006 which resulted in secondhand smoke [SHS] being declared a "toxic air contaminant." There are several published scientific studies of SHS in the outdoor air in addition to this report, and they are reviewed in a paper listed on my website < > under recent reports. These reports show that outdoor SHS may often be as high as indoor SHS in proximity to smokers. … I suggest that you revisit this issue, and see if you want to retract your erroneous statement.


So let's revisit the issue. Let's look at those studies.

In a fact sheet  summarizing the studies, Repace writes:

The California Air Resources Board study (CARB, 2006), measured OTS [outdoor tobacco smoke] nicotine concentrations outside an airport, college, government center, office complex, and amusement park. CARB found that at these typical outdoor locations, Californians may be exposed to OTS levels as high as indoor SHS concentrations. …

Klepeis, et al. (2007) measured OTS respirable particle concentrations in outdoor patios, on airport and city sidewalks, and in parks. They also conducted controlled experiments of SHS indoors and OTS outdoors. Klepeis et al. (2007) found that mean SHS particle concentrations outdoors can be comparable to SHS indoors.

Both studies were done in California. Let's start with the CARB report. Here are some relevant passages:

1) It is difficult to measure ETS removal rates in outdoor settings since outdoor conditions are highly variable and change rapidly. (Page III-13)

2) [C]igars and cigarettes, the primary source of ETS [environmental tobacco smoke], are smaller sources that emit pollutants near people and thereby exposures to ETS are very localized. (Page II-4)

3) Overall, the results indicate that concentrations of nicotine correspond to the number of smokers in the smoking areas, although factors such as the size of the smoking area and wind speed affected the results. (Page II-3)

4) For each sampling period, two samplers were situated adjacent to the outdoor smoking area, with a third sampler located away from the smoking area as a background sampler in the expected upwind direction. … At most sites, the location of the background monitors, due to physical obstacles and/or meteorological conditions, were close to the smoking areas. … However, even at the background site locations, background concentrations were substantially lower than measured in the smoking areas. (Pages V-7 to V-8)

So Repace is correct that secondhand smoke has been studied outdoors. But the CARB study underscores what I wrote: "[T]hose studies aren't conducted in wide-open spaces. They can't cover the whole atmosphere." The passages quoted here confirm that 1) it's hard to measure smoke dynamics outdoors because conditions change rapidly; 2) exposure levels are "very localized"; 3) wind, area size, and number of smokers affect the degree of exposure; and 4) even close to a designated smoking area, you can avoid exposure by being upwind. At the amusement park, for example, the difference in exposure was a factor of 25.

Now let's look at the Klepeis study:

1) average OTS concentrations measured … during visits to outdoor patios that were enclosed by fences or walls … were 50% and 43% higher, respectively, than those observed in more open areas. … (Page 10)

2) We observed a clear reduction in OTS levels as the distance from a tobacco source increased. Generally, average levels within 0.5 m from a single cigarette source were quite high and comparable to indoor levels, and OTS levels at distances greater than 1 or 2m were much lower. (Page 12)

3) At distances larger than 2 m, levels near single cigarettes were generally close to background. … [If] one spends time downwind from a smoker, then moving to a distance of more than 2m can reduce the likelihood of experiencing elevated particle exposure due to OTS. (Page 14)

Again, the data confirm common sense. The more open the space and the farther away you are, the lower your smoke exposure. To get the kind of exposure you'd suffer indoors, you have to stand within two feet of the smoker. Move seven feet away, and you're "close to background," i.e., breathing normal air. I recommend greater distance than that, just to be safe. But you don't need to ban smoking throughout Central Park.

Repace offers additional arguments  for outdoor smoking bans. He points out that "there are millions of asthmatics in this country" and says outdoor smoke levels can be "high enough to trigger an asthmatic attack in susceptible persons." He also contends that "most nonsmokers find SHS to be a nuisance. Just as noise and dog droppings are regulated in public spaces, governments have the right and the obligation to protect the susceptible from the stupid."

If you want to argue for parkwide smoking bans based on asthma or on an analogy to noise pollution, go ahead and make that case. But let's not cloud that debate by invoking the general harm of secondhand smoke. Studies of secondhand smoke have indeed moved outdoors. Their findings support restrictions on lighting up within a few feet of other people. But they don't warrant more than that.

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