Alpine Living Air model XL-15 ozone air purifier, $25.

You're advised to learn more about the different brands of air purifiers on the market, because you'll see them at yard sales regularly and some brands sell quite well on eBay. What's interesting about the Alpine 'Living Air' machines is that they're not filters. Aside from the coarse aluminum mesh on the back side, there's not even a filter element inside. So, how do they work?

The Living Air unit in this example is known as a 'corona discharge' purifier, because it uses electrically-created ozone to purify the surrounding environment. One way to create ozone is to use electricity to bond oxygen molecules together. In its natural state, oxygen atoms are paired up to form molecules of O². But the introduction of electricity causes an unstable bond to occur between three atoms of oxygen, forming O³, or ozone. The ozone in nature is created by lightning.

Ozone, no matter how it's produced, is a highly unstable molecule that reacts with nearly everything it encounters. In the case of ozonating air purifiers like this Alpine Living Air, most of that interaction fortunately occurs with indoor air pollution. Ozone molecules float around in the air until they contact a foreign particle, at which point the extra oxygen atom splits off and attaches itself to the particle. The introduction of this new oxygen atom oxidizes the particle, transforming the foreign particle into hydrogen and carbon dioxide. The remaining oxygen molecules are left as pure oxygen (O².) Ozone will react with thousands of pollutants with this same destructive process, which explains why little units like this XL-15 can literally remove odors and pollutants, instead of simply masking them. But how do these machines make ozone?

A corona discharge air purifier can be thought of as a sort of 'thunderstorm in a box.' Blasting 5,000 to 10,000 volts across the glass and metal plates inside the unit (which can be seen in the photos,) simulates the electrical effects of lightning, creating the required electrical arcing needed to generate ozone. The ozonated air is then ejected out the front of the purifier, where it cleans the air and makes everything smell fresh and clean.

As a matter of fact, you can actually see this process in action. On the front of this machine are two knobs - one controls the speed of the fan motor, and the other controls the ozone concentration by varying the amount of current running across the ozone-producing plates. As you turn the concentration knob up toward full power, you can hear and see the electricity arcing around inside the purifier, creating the ozone.

Despite these machines' popularity nowadays, there is a word of warning due about the effects of ozone. Ozone occurs naturally in the environment and is critical to our survival because it serves the very important function of keeping the planet from getting roasted by the Sun's ultraviolet rays. But despite this fact, and the wonderfully glowing reviews these purifiers enjoy, certain health risks have been associated with the use of ozone generators indoors. Excessive levels of Ozone can cause coughing, wheezing, painful breathing, nasal congestion, sore throat and nausea. So, please feel free to buy these to sell on eBay, but think seriously about using them in your own home!

Here are a couple of final thoughts on these machines.

Whenever you're thinking of buying one of these machines to sell, turn it on if at all possible. Obvious, I know, but it always bears repeating. Turn the fan speed up and down. Adjust the ozone knob and listen to the crackling sound change. You should be able to smell the ozone. Find a store that sells ozone air purifiers and smell the output from one that works. I can't describe the smell to you, but once you know the smell, you'll always be able to tell if a machine you're contemplating buying is making ozone or not!

Look inside the back of the unit and check for any corrosion or rust. Built-up dust and dirt is one thing, but I've seen too many of these little machines that looked as if they'd been pulled out of the ocean in a shrimp net - rust and corrosion all over the insides! Your eBay buyers don't want rust or corrosion inside their machines!

When you find one of these units, always remove the rear cover to ensure that the ozone plates are not only present, but are also intact and free from damage. These plates are very thin glass and can break very easily. And since these plates cost about $15 apiece to replace, any that are damaged or missing can really eat into your profit!

That little black knob on the lower right-hand side of the back of the unit unscrews to reveal a little fuse. Make sure that little fuse knob is in place! I remember getting home one day with a beautifully cleam little XL-15, only to discover that someone had removed the fuse holder knob, rendering the machine inoperative until I was able to replace it.

Finally, if you look at the picture of the rear of the machine above, you'll notice a small square cutout in the lower right corner of the filter cover. This is the safety switch that prevents the machine from running if the rear cover is off, which is necessary considering the very high voltages that are used in these machines. There's a small plastic tab on the bottom of the rear screen that depresses the safety switch when it's installed onto the rear of the unit. Sometimes this tab breaks off, moves out of place, or in some other way fails to depress the switch when the cover is installed. This fools the machine into thinking that the cover is off, preventing it from operating. I've bought several 'broken' purifiers that turned out to work perfectly after correcting this one little problem!

This Alpine 'Living Air' XL-15 air purifier sold on eBay for $119.

Photo of Alpine Living Air XL-15 air purifier