New York City Council passed the ban on smoking in its parks and on its beaches on the principle that a nonsmoker shouldn't have to inhale even a tiny amount of secondhand smoke, whether in a bar or a Central Park meadow. But while there is a strong public-health case for banning smoking indoors, the case for banning it outdoors is much weaker—particularly when it runs the risk of a backlash that could undermine the basic goals of the anti-smoking movement.

True, there is evidence that being near someone smoking, even outdoors, can result in significant secondhand smoke exposure. Researchers at Stanford found that levels of tobacco smoke within three feet of a smoker outside are comparable to inside levels. But no evidence demonstrates that the duration of outdoor exposure—in places where people can move freely about—is long enough to cause substantial health damage.

But that hasn't stopped many opponents of smoking. Citing new research, they have argued that even transient exposure to tobacco smoke can cause severe health effects like heart disease and lung cancer. For example, last year the surgeon general's office claimed that "even brief exposure to secondhand smoke can cause cardiovascular disease and could trigger acute cardiac events, such as heart attack," and that "inhaling even the smallest amount of tobacco smoke can also damage your DNA, which can lead to cancer."

However, the surgeon general's statement confuses the temporary negative effects of secondhand smoke on the circulatory system, which have been shown to occur with short-term exposure, with heart disease, a process that requires repeated exposure and recurring damage to the coronary arteries. It also confuses onetime DNA damage, which occurs with any carcinogenic exposure, with cancer risk, which likewise generally requires repeated exposure.

Moreover, bans like New York's may actually increase exposure by creating smoke-filled areas near park entrances that cannot be avoided.

To make matters worse, in trying to convince people that even transient exposure to secondhand smoke is a potentially deadly hazard, smoking opponents risk losing scientific credibility. The anti-smoking movement has always fought with science on its side, but New York's ban on outdoor smoking seems to fulfill its opponents' charge that the movement is being driven instead by an unthinking hatred of tobacco smoke. That, in turn, could jeopardize more important fronts in the anti-smoking fight, in particular the 21 states that still allow smoking in bars and restaurants.

A ban on outdoor smoking may provide a symbolic victory. But from a public health perspective, it's pointless. Instead, anti-smoking organizations should focus on extending workplace protections, already enjoyed by millions of New Yorkers, to the 100 million Americans still denied the right to work without having to breathe in secondhand smoke.