You know that "new-car" smell? No? Well, how about that "dusty, musty old-car" smell? You may be able to fix either problem by getting to know your car's other air filter -- not the one that the guys at Swifty Lube show you. That's your engine's air filter. There's another filter for the air you breathe, which no one ever talks about (or does anything about), and that's your "cabin" air filter.

Why should you care? New or old, cars tend to smell. And smell means that your body is being exposed to various organic compounds, particulate pollution, mold spores, smoke, road dust, perfumes and probably radioactive dust mites from Mars, if the truth -- which is out there -- be known.

The new-car smell is often OK from an aesthetic standpoint, but totally objectionable from a health standpoint. (Well, okay, a sit-point, unless you own a bus.) The new-car smell comes from the evaporation of organic compounds from all the lovely synthetics, and perhaps even the treated natural materials like leather or fireproofed fabric, in your car. Plastics of all sorts volatilize (go from solid to gas), especially in the heat. You may also be spreading around cleaning or shining compounds that will volatilize.

What sort of stuff might you be breathing in your new car? An Australian study of new cars found the following:

• Benzene - a carcinogen
• Acetone - a mucosal irritant
• Cyclohexanone - a possible carcinogen
• Ethylbenzene - a systemic toxin
• MIBK - a systemic toxin
• n-Hexane - a neurotoxin
• Styrene - a likely carcinogen
• Toluene - a central nervous system disruptor
• Xylene isomers - a fetal development toxin

Tests of 101 new cars in 2004 by the Osaka Prefectural Institute of Public Health found 241 such toxins, including other carcinogens. Tests in Taiwan found one car with 200 times the safe limit of certain toxins.

Airborne toxins in new cars often start out at concentrations well above established "safe" limits, and safe limits for compounds in combination are generally not known. Tests found cars with three to four times the VOC concentration as that found in new buildings, which is two to four times the level at which respiratory problems may emerge in some people (10 mg/m³). Fortunately, after about 6 months, the levels generally drop to acceptable levels.

Moreover, good ventilation during that early period can come close to eliminating these substances from your air. Drive and park with your windows open as much as possible for the first six months, or use the car's ventilation system in the "fresh air" (not "recirculate") mode. You can change the air completely about 20-30 times per minute, which is vastly better than in a typical residence or office.

Or -- consider replacing the "cabin" air filter in your new car with an aftermarket brand containing carbon. Carbon filters do an excellent job of removing VOCs from air and water. You may, however, find it difficult to locate a carbon filter. You may also want a mechanic to do the replacement job, unless you are comfortable with your skill in removing and replacing plastic car panels.

Even if you can't find a carbon filter or don't have a new car, you may want to consider replacing your cabin air filter at major service intervals while the car's in the shop anyway. If the level of gunk I found in my cabin filter is any indication, you stand a good chance of reducing any allergic reactions you suffer after driving, and of reducing persistent musky odors. (They may even be coming from your air filter at this point!) You may also slightly improve the efficiency of your ventilation and air conditioning, and enjoy better air flow at lower fan settings.

I checked the owner's manual for our 2007 Subaru Forester (50K miles), and it indicated that we "might" have such a filter. It showed with diagrams how to remove the filter from behind the glove compartment. After removing seven screws and two unseen plastic panel fasteners of the "pull and pray" variety, I discovered that we do have a cabin air filter, and boy, was it dirty! The photos below show how I accessed the filter and the crud I found in it.

I tried cleaning out the filter by vacuuming (from the dirty side) with a 5 HP shop vacuum. Apart from removing the leaves, it did little. The same amount of dirt appeared to be trapped in the filter fiber.

So, next time you are bringing your car in for a major service interval -- or if you are buying a new or used one -- have them replace your cabin air filter. See if they can find a carbon filter if you have a new car (or your old one smells of plastic), or find one online for them. Chances are, you'll breathe a lot easier.