As St. Louis voters prepared to cast their ballots on clean indoor-air laws last fall, opponents trotted out a familiar argument:

“Modern filtration systems have all but eliminated the dangers of secondhand smoke,” wrote Bill Hannegan, who headed a group opposing the smoking bans, in a letter to the Post-Dispatch.

It’s a seemingly compelling argument with an interesting provenance.

Unfortunately, it turns out not be true. Washington University researchers measured nicotine levels in 10 bars and 10 restaurants in St. Louis County. Their results were released last week: Places that allow smoking had 31 times more airborne nicotine than those that don’t.

Fully half of the establishments tested had ventilation systems. The ventilation systems didn’t help.

Bars and restaurants with ventilation systems actually recorded higher nicotine levels than restaurants and bars with no ventilation systems. Researchers suggested that may be because of the ventilation systems “recycling the air back into the same space.”

The American Society of Heating, Refrigeration and Air-Conditioning Engineers — the people who sell, design and install ventilation systems — wouldn’t be surprised at those results. The group issued a statement in 2005 saying that ventilation systems cannot protect against secondhand smoke.

A Tufts University study of restaurants and bars with state-of-the-art ventilation systems reached the same conclusion in 2006. That same year, U.S. Surgeon General Richard Carmona reported that filtration systems don’t work.

A 2008 study on nicotine levels in 10 St. Louis bars reported that indoor air pollution levels in bars that allow smoking were six times higher than in those that did not.

Notice a pattern here? Mr. Hannegan doesn’t. He told Post-Dispatch reporter Blythe Bernhard last week that he’s not willing to concede the point.

It turns out that the idea that ventilation is the solution to secondhand smoke came from the tobacco industry. We are shocked, shocked.

A 1988 strategy document prepared by the Tobacco Institute, an industry front group, laid out the rationale: “The argument of ‘freedom of choice’ with regard to workplace smoking is becoming increasingly difficult to sell. The concept of ‘indoor air quality’ (with an emphasis on science) has much more credibility and will draw a wider audience.”

That document is among thousands that became public after attorneys general from 48 states settled a lawsuit against the tobacco companies in 1998.

The Tobacco Institute’s report set out a strategy to “promote ventilation as the best solution to all indoor air-quality problems, including smoking.”

At about the same time, Philip Morris was launching its “ETS (environmental tobacco smoke) Strategy.” It’s goal, according to another document marked confidential, was to use “clean-air technology as a means of promoting smoking tolerance.”

The document lays out plans for downplaying the risks of secondhand smoke, as well as a plan of attack on what the company calls “‘politicized’ science.”

It’s no surprise that 20 years later, addicts and apologists are using the same playbook in their rear-guard defense of smoking. The surprise is that anyone would pay attention to them.

After all, since those strategic smokescreens first were dreamed up 22 years ago, 9.5 million Americans have died from tobacco-related causes.