There are lots of small cigarette lighter plug in "air purifiers" sold nowdays. Most are not up to the automobile cabin air quality challenge.

Howard Hughes, the eccentric billionaire, once had a car air purifier installed in a limousine. The purifier cost more than the limo, weighed almost as much, and and took up most of the trunk. A $20 device weighing a few ounces cannot assure safe air in a modern car cabin.

We tend to feel safe in our car, but the air in the interiors of cars may be even worse than household indoor air. Driving a car can be our single most toxic activity.

A busy interstate highway has many sources of pollution; gas and diesel exhaust fumes, various particles, pollen, cigarette smoke, and germs.

Everything along the road has an oily finish, with tiny soot particulates waiting to flurry into the air an auto moves through

As air rushes over the exterior metal skin, negative charges are stripped away. A positive ionic charge builds up in auto interior air, causing stimulation followed by fatigue. This is why the car air ionizer has become so popular.

Flow-through ventilation is required by law: even when the A/C is set to recirculate, all vehicles still exchange some outside air to maintain oxygen in the car's interior.

That "new car smell" that so many people confuse with success comes from evaporating plastics and glues.

Wet carpeting, insulation, or air conditioning drip can allow mold to grow inside a car.

Many automotive cleaning products can be toxic in a car's air. Interior air freshener sales continue at a rapid pace, despite health concerns.

A vehicle interior is smaller than residential rooms: smoking and side stream smoke are especially concentrated inside an already toxic car. Rooms can be repainted, carpets and furniture removed. Tars and particlulate from smoking can never be removed from automobile headliners and upholstery.

There are many models of auto air purifiers available. China exports thousands of products, which emanate from the low budget mom and pop electronics explosion there. Most are small ionizers, with plugs for the car's 12v DC cigarette lighter socket. Few have any ability to actually purify air in cars. Most make significant ozone.

As with indoor room air purifiers, better car purifiers have real fans and activated carbon for toxic chemicals. Some can also do double duty as a travel air purifier, using an optional AC power adapter.

A couple real car air purifiers to check out; Aireox D-22, and Amaircare Roomaid Portable. The Nanobreeze photocatalytic car model clips onto air vents, using the vehicle's ventilation system and fan.