You think you’ve got trouble? In China there are 2-million-year-old accumulations of dust (called loess by geologists) that are more than 1,000 feet (300 meters) thick. But it’s not due to sloppy housekeeping.
The dust has been swept up by winds from the Gobi Desert. In certain locations where the winds die down, they drop their loads of dust particles. The resulting huge dust piles became compressed from their own weight over the years, and some of them have actually been hollowed out into cave dwellings.
But never fear. At the rate at which the dust has accumulated in the Chinese loess cliffs, you could stop dusting in your house for a hundred years and still have a layer that is no more than an inch (2 centimeters) thick.
Unless you live near the Gobi Desert, you may be wondering where all the dust in your house comes from.
The dust in our atmosphere has many sources. Winds blow over dry earth, such as plowed fields, dirt roads and deserts. Plants give off pollen and other particulate matter. Forest fires and volcanoes can spew dust and smoke particles high into the upper atmosphere, where they may blow around for years before settling. There is less dust over the oceans than over land, but still there are tiny bits of dried salt spray and even ash particles falling from meteorites that burn up in the atmosphere.
And, you’re thinking, it all winds up on your bookshelves, right? Well, we’re not done yet. Let’s take a close look at the household dust that you generate yourself.
Notice that dust settles only on horizontal surfaces such as sills, shelves and the top edges of picture frames. (Forgot about those, didn’t you?) Therefore, the stuff must be falling out of the air under the influence of gravity. That means that the particles of dust must be bigger than a certain size; if they were any smaller, the constant, agitated motion of the air molecules would keep them permanently suspended.
That’s the case with cigarette smoke, for example, the individual particles are so small that the bombardment of air molecules keeps them from falling. On the other hand, if dust particles were too big they wouldn’t have been wafted into the air in the first place, later to come to rest upon that ugly china fig-urine that Aunt Sophie gave you.
But it’s not all a matter of particle size. A relatively big tuft of lint from your clothing will float on the air because of its feathery shape, and this too will eventually find a landing pad someplace where you’d rather not have it. Those dust bunnies that take refuge in the windless climate under your bed are made up largely of fibers from clothing and other fabrics, often tangled together with fallen human or pet hairs and flakes of skin. (I never said this would be pretty.)
Everything that moves inside your house has the potential for sending out microscopic bits that are worn off and carried into the air. When a high traffic area on your carpet wears out, where do you think all those carpet fibers went? Mote by mote, they wound up scattered around the house, to be dealt with on cleaning day.
Which brings up the question of how effective dusting really is. It depends a lot on how you do it. A dry dust cloth might just redistribute the dust, moving it perhaps from the shelf to the floor, demonstrating “to dust shall it return” in the literal, rather than the biblical, sense. Rubbing with a dust cloth can actually be counterproductive, because it can produce an electrostatic charge on the dust particles. Once charged, they can adhere tenaciously to any nearby object, so they will simply have been transferred from one object to another.
A dust cloth with a downy nap that traps the dust particles is one good idea. Another is to use one of those commercial dusting sprays. They contain an oil that not only makes the dust particles stick to the cloth, but coats them with a thin insulating layer so they can’t adhere electrostatically to nearby objects.
For a surprising glimpse of how much dust there actually is in the air, look up at the beam of light coming from the projector the next time you go to the movies.
The reason you can see the beam at all is that the light is being scattered sideways by ordinarily invisible dust particles that are approximately the same size as the light’s wavelength.