Car exhaust vs. secondhand smoke

You may have heard it during this year's debate about a Minneapolis smoking ban: "Ban smoking in bars and restaurants? Why don't you work on something more important -- like pollution from cars?"

The smoking ban passed, but the question lingers: is outdoor exhaust worse than indoor smoke?

According to Greg Pratt, a scientist researcher with Minnesota Pollution Control Agency Environmental Impacts division, when it comes to gauging risk on a per-person basis, nobody has a clear answer.

That doesn't make the question one to discard.

Pratt and other pollution experts say that in many ways comparing car and cigarette smoke is like comparing toxic apples and oranges -- but understanding the harm from each is important.

Roughly speaking, cigs and cars are more like air pollution royalty; secondhand smoke reigns as the top indoor air pollutant and auto exhaust takes top honors once you step outside the door.


A handful of researchers have taken a stab at disentangling car and smoking exposures. Their results have been mixed; some indicate that one is worse than the other, while others say they're roughly equal.

One study conducted this fall at Tufts University School of Medicine in Boston, declared that secondhand smoke is by far the worse of the two pollutants when comparing the carcinogenic particulate matter of a smoky bar or casino with outdoor air near an Interstate at rush hour. However, a Swedish study showed that benzene exposure is higher inside a car than in an average smoky caf/ (benzene is present in both car exhaust and smoke). Keep digging and points can be made on either side, bouncing back and forth like a ball in a tennis match.

Pratt and other air-toxin experts note the difficulty in producing a definitive study. Is your secondhand smoker an occasional espresso drinker in a well-ventilated caf/ or a veteran server in a smoke-yellowed pool hall? Is your driver someone who keeps the windows up and the A/C on, or who prefers a good hair-tossing breeze -- and whatever contaminants may float in on it?

Another problem is that exhaust and smoke toxins overlap. Both contain oxygen-reducing carbon monoxide, for example, as well as cancer-causing benzene among other carcinogens. Each also contains myriad substances for which tolerance varies, chemical-by-chemical and person-by-person.

Given the considerations above, however, Pratt and others, including representatives from the American Lung Association -- the only Twin Cities group that works on both car and cigarette smoke -- refuse to play the "why don't you go work on that other pollutant" game.

They say it's better to work with what we know, the impact of each form of pollution.

Bad apples

– Secondhand smoke causes 40,000-60,000 deaths each year, according to the American Lung Association and government agencies, making it the leading cause of preventable death.

– Consistent Environmental Tobacco Smoke (ETS) exposure coincides with a 20 percent higher risk of heart problems.

– In addition to numerous types of cancer, ETS has been linked with asthma, pneumonia, bronchitis, ear infections (which can be fatal in children), and other respiratory diseases and conditions.

Being near someone who's smoking, most likely indoors, is a risk to your health. However, step outside and ETS is the least of your worries. Unless you're standing right next to a smoker, secondhand smoke can't compete with car exhaust, or pretty much any other source of air toxins. Smoke, says Pratt "is a very small part of the outdoor air pollution problem."

However, this doesn't mean smoking isn't bad for the environment. From the growing of tobacco to cigarette and cigar waste, environmental problems abound.

– Most tobacco, which is grown in 20 states and many developing nations, is grown using large amounts of pesticide toxic to humans and animals alike. (Researchers found that 60 percent of quail killed by hunters in a tobacco-growing community had insecticides in their bodies.)

– One average-sized tree is cut down to make the paper for approximately every 300 cigarettes (about a two-week supply for a pack-a-day smoker).

– And while butts may look like innocuous cotton, they're actually a stringy plastic that takes an average 25 years to decompose. In their lifetime, the plastic makes its way from streets to storm sewers, to rivers, lakes and the ocean. They then turn up in the gullets and stomachs of fish, water birds and marine mammals (such as seals), which can't digest them and subsequently die.

Rotten oranges

Although technology has decreased pollution coming out of most tailpipes, the more cars per household, bigger vehicles and more miles driven annually nullify many of these gains, according to the Minnesota Pollution Control Agency (MPCA).

– Mobile sources such as cars and trucks account for 52 percent of outdoor air pollution in Minnesota, according to the MPCA.

– Exposure to air toxins from mobile sources (including cars and trucks but also planes and construction vehicles) is considered responsible for approximately 53 percent of Minnesotans' excess cancer risk, also according to the MPCA.

– Exposure to fine particulate matter -- caused primarily by sulfur dioxide and nitrogen oxides from cars -- is linked to increases in respiratory health problems, hospitalization for heart or lung disease and even premature death.

– Car exhaust provides the main ingredients for ground-level ozone, which causes inflammation of airways and reduced lung function. Ozone increases correlate with spikes in emergency room visits by asthmatics and with higher hospital admissions in general the day following high ozone exposures.

– Planet-wise, car exhaust has long been known as a contributor to the greenhouse effect. And the ecological impacts of the oil industry are also generally recognized, from the drilling to transport of oil (with its inevitable accidents or spills).

– The Centers for Disease Control estimates that of the United States population that lived in metropolitan areas in 2002: 51 percent were exposed to harmful levels of ozone, 14 percent to harmful levels of particulate matter and 16 percent to carbon monoxide. All pollutants are car-related and much lower in rural areas.

Sources: Minnesota Department of Health, Minnesota Pollution Control Agency, Environmental Protection Agency, Centers for Disease Control, United States Office of the Attorney General, The Ocean Conservancy and "Tobacco Control" journal.