The product: Dust, cigarette smoke, pollen and pet dander: With so many irritants floating around our homes and work places, clean air is a hot commodity. Americans spend hundreds of millions of dollars on furnace filters and air cleaners each year. Though some consumers are simply trying to bring a little extra freshness into their lives, many others hope that their investment will help relieve their asthma or allergies.If you've ever shopped for an air cleaner -- or if you've ever idly flipped through a SkyMall catalog -- you've undoubtedly seen ads for ionic air purifiers, devices that take an unusual approach to clearing the air. Instead of relying on fans to move air through filters, the machines release a steady stream of negatively charged ions that electrify the bits of dust, dander or other flotsam. The airborne particles pick up the negative charge and become strongly attracted to positively charged collection plates inside the machine. (In many cases, they also become attracted to other charged surfaces such as walls, table tops and TV screens.)

Except for a few models that use fans to help suck in the charged particles, most ionic air purifiers work silently. And, as ads are quick to point out, the devices generally don't have any motors or moving parts, and there are no filters to replace.There's another thing that separates ionic air purifiers from other technologies: To varying degrees, all ionic air purifiers release ozone, a potential pollutant. A 2006 study by researchers at UC Davis found that one popular brand, the Ionic Breeze Quadra, released about 2.2 milligrams of ozone per hour, or about as much as a constantly running photocopier. (Ionic purifiers shouldn't be confused with ozone generators that are marketed as "air cleaners." By design, these devices can release 50 to 200 milligrams of ozone per hour.) Ionic purifiers are sold at drugstores, at department stores and via the Internet. The well-known and heavily advertised Ionic Breeze line is one of the cornerstone products of the Sharper Image, the high-end gadget store.

One current offering, the Ionic Breeze GP, stands more than 2 feet tall and as an added feature comes equipped with a UV light to help kill airborne germs. If you buy one for $400, the second costs $200. The Sharper Image also sells a 13-inch unit for $150. You can buy a 28-inch Ionic Pro Turbo Air Purifier from Wal-Mart for $180. An online company called Heaven Fresh sells the table-top XJ-2000 ionic air purifier for about $50.The claims: According to the Sharper Image website, the Ionic Breeze is "proven effective at reducing airborne allergens and irritants -- with no fan, no motor and no noise." Car Tyres In BristolThe Heaven Fresh website says that its purifiers can provide relief from "asthma, bronchitis, hay fever and other respiratory diseases." Second Hand Wedding Dresses Northern BeachesHeaven Fresh also claims that the ozone emitted by its machines helps clean the air. Ceiling Drapes For Bedroom

According to the site, "ozone is one of the purest and most powerful oxidants and germicides known."The bottom line: Ionic air purifiers have undeniable appeal, but there's a problem: They don't really improve air quality, says Dr. James Sublett, a clinical professor at the University of Louisville; a fellow at the American College of Allergy, Asthma & Immunology; and co-chair of the 2007 ACAAI Healthy Indoor Environment conference. "We [allergists and immunologists] generally don't recommend them," he says. "This is a windmill that I've been tilting at for a number of years."According to Sublett, the devices don't effectively remove dust, dander and other irritants from a room. Without fans, he explains, they can't collect airborne particles from more than a few feet away. And when even small amounts of dust enter the device, the plates inside quickly lose much of their power to attract more particles. Meanwhile, the charged particles that stick to walls or TV screens haven't left the room and can always billow up again to cause trouble.

The ozone released from the devices is another deal-breaking shortcoming, Sublett says. "Ozone is a pollutant and an irritant. Even small amounts are too much." People who use several units at a time are especially likely to get an ozone overload, he says. One of Sublett's patients noticed a great improvement in her breathing when she turned off the six ionic purifiers in her home.The California Air Resources Board recently banned all devices that create an ozone concentration of more than 50 parts per billion, starting in 2009. Under normal conditions, ionic purifiers (as opposed to ozone generators) would fall below that threshold, says Jeffery Siegel, an assistant professor of civil, architectural and environmental engineering at the University of Texas at Austin who has studied the devices in laboratories as well as his own bedroom. Still, he says, the new standard is misleading because even products that release small amounts of ozone could easily reach that concentration in small, poorly ventilated spaces.

Sublett says people with asthma or allergies should consider installing high-efficiency particulate air (HEPA) filters in their heating or cooling systems. The ultra-fine mesh on these filters traps all sorts of irritants that would otherwise circulate through the home.Is there a consumer product you'd like the Healthy Skeptic to examine? I've become a bit of an air purifier nut over the years. Originally, I used them because I believed that they helped keep the dust down and my dirty home cleaner. Now, I've come to appreciate cleaner air quality while I suck it in all night. When you open it up and see how dirty the filters are, you have to be glad that you have one. With indoor air much more polluted in general than outdoor air, having a quiet, energy efficient air purifier in your home should be, in my opinion, an integral part of your home design plan. What Is a HEPA Filter (and why should I care?) In the air filter world, the HEPA standard has evolved as the go-to "good enough" quality level.

Developed originally during WWII by the Atomic Energy Commission's Manhattan Project to clean radiation out of the air, the design evolved over a number of years into an affordable, mass-produced paper filter system that could be integrated into purifiers, vacuums and other units for commercial and residential use. To qualify as HEPA by US government standards, an air filter must remove (from the air that passes through) 99.97% of particles that have a size of 0.3 µm. "HEPA: High-efficiency particulate arrestance or HEPA is a type of air filter. Filters meeting the HEPA standard have many applications, including use in medical facilities, automobiles, aircraft and homes. The filter must satisfy certain standards of efficiency such as those set by the United States Department of Energy (DOE)." via Wikipedia Here are my top picks for the year, updated from 2010. I totally believe in the super affordable fan and filter based machines, but for better filtering (particularly for odor and allergy sufferers) and quieter filtering, I would recommend spending more.

Kenmore 83394 Small Room HEPA Filter Air Purifier Spoken of highly by readers, this Sears Kenmore series, available in three sizes, is the most affordable HEPA air purifier that I'm including on the list. It features a sleek, wall hugging design, quiet operation, an EnergyStar rating and a two-filter system that covers up to 400 square feet. Honeywell 50250-S True HEPA Air Purifier, 390 sq ft I like Honeywell, and I've also had two of these purifiers for a number of years in our many roomed family house in the country. Big, not particularly quiet (great white noise, however, for sleeping babies & adults), I find the Honeywell purifiers to be simple with very good HEPA filters at a very good price for basic air filtration. This purifier is rated to clean a room up to 390 square feet (smaller than RabbitAir) and is not for continuous air cleaning as it's too loud and not an energy saver. Coway AP-1512HH Mighty Air Purifier with True HEPA and Eco Mode Rated super highly by The Sweethome, Coway is a name I hadn't heard before, but its products are given high marks for air cleaning at a very good value.

Said to be as good as machines twice the price, the Coway Mighty is a small, sleek unit that runs silently, uses very little energy and works with easily replaceable filter panels similar to a RabbitAir machine. It will efficiently clean a 325 square foot room. What Happened To Air Ionisers??? Famous just a few years ago for being slim, silent and able to clean the air without a breeze (remember how popular they were among those that needed to clear the air quickly in their parents' house?), air ionisers have faded in use because two things happened. The first was that ionisers were discovered to produce small amounts of ozone, a toxic gas, which set off a health scare and made them persona non-grata in the medical community. Secondly, and more importantly, ionisers have never proven to clean air and move it through the room as well as traditional HEPA filters. Famously, in 2003, Consumer Reports gave The Sharper Image's popular Ionic Breeze a "fail" rating, which set off a lengthy court battle.

In the end, Sharper Image lost the case when it couldn't prove any of Consumer Reports assertions to be untrue. That said, ionizers have found their way into many HEPA machines as a way of adding extra filtering power. RabbitAir BioGS 2.0 Ultra Quiet Air Purifier Designed by Guto Indio da Costa in 2014, this purifier won the Good Design Award and the RedDot Award in that year. This (and the MinusA2 Ultra Quiet Air Purifier a few products down) are me two top picks of all the machines on this list. I have them at home, and I find them to be compact, powerful and silent. Mine runs continually on low and I've had it for three years without any problems. Dyson Pure Cool Link Tower Since its inception, Dyson has always been known for breaking the mold with its innovative products. Consider this the air purifier of the future. With the corresponding app, the machine monitors the humidity, air quality and temperature of the room it's in and reacts accordingly, reporting all stats back to you via your smart phone.

It promises to remove 99.97% of allergens and pollutants as small as 0.3 microns. RabbitAir MinusA2 Ultra Quiet Air Purifier SPA-780A Black This is the more expensive of RabbitAir's offerings, and it's the one that I have had for years. The MinusA2 sits flat against any wall or piece of furniture, runs absolutely silently and comes with a choice of four different filter systems: Pet Allergy, Odors, Toxins or Germ Defense (they all seem good to me). The unit sips energy with an EnergyStar rating (as low as 7 watts), is a true HEPA filter and covers from 700-815 square feet at normal filtration levels (cleaning for an allergy sufferer reduces the square footage to about half). Alen BreatheSmart Customizable Air Purifier with HEPA-Pure Filter for Allergies and Dust , it also has a near perfect 5-star rating on Amazon. Cleaning up to 1,100 square feet, it covers more space than any other purifier on this list. Like the Dyson air filter, it automatically detects and adjusts to fluctuating air quality.

Fully customizable, buyers get the choice of 4 HEPA filters (Pure, Silver—which is best for allergy sufferers, OdorCell, FreshPlus.) Also, for the design aficionado, the BreatheSmart is offered in 15 front panel options, one of them that you can custom paint to make your walls.Founded in the '90s, Stockholm-based Blueair pairs a high standard of filtration with a sleek, Scandinavian design. With a large range of excellent machines at prices from medium to very high, Blueair features HEPA filtration, galvanized steel casing, super quiet operation, no drafts, extreme energy efficiency, and an argument for the highest Clean Air Delivery Rate (CADR) on the market, which means it will move air more quickly as it cleans. The Classic ECO10 shown here will handle 220 square feet. IQAir New Edition HealthPro Plus IQAir has a great history as it was founded by two brothers, Manfred and Klaus Hammes, who were early pioneers in the '60s developing paper-based filters to eliminate coal dust coming out of ovens in German homes.