The three main sources of household dust

The three main sources of household dust:

 

1. Cleaning

2. Cooking

3. Movement

No wonder my house is so clean.

What with my rather sporadic housekeeping (Mario Buatta once remarked that dust protects furniture from sunlight wonderfully), heavy reliance on the microwave and movement pretty much confined to my treadmill (which accumulates dust underneath remarkably fast and in huge quantities spiked with Gray Cat hair but is easily removed since it's bundled in one place), my house is just so spiffy.

I learned a lot about dust and its discontents in Michael Tortorello's story in yesterday's New York Times Home section; excerpts follow.

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Apparently, the amount of airborne dust doubled in the 20th century, according to a recent paper in the journal Atmospheric Chemistry and Physics.

The claim sounds outlandish. The amount of dust in the world — like the amount of sin or acne — must be a constant. The finding was somewhat surprising even to Natalie Mahowald, the lead researcher on the study and an associate professor of atmospheric sciences at Cornell University.

Although she was working with inchoate historical data, Dr. Mahowald said, "Nobody has come up to me and said, 'I don’t believe you.'" Climate change seems to be one source for all the new dust. Human land use is another. Anyone looking for a scapegoat — and that’s all of us, isn’t it? — can start with the droughts and desertification in North Africa, she said.

Dr. Mahowald said, "Dust is such a vague term. I’m being very particular here: soil particles suspended in the atmosphere."

Cleaning can have an unintended consequence: Oddly enough, it actually breeds dust. In fact, cleaning is one of the three main sources of household dust, according to research on indoor particles. Cooking is the second; movement is the third.

Every step disturbs tiny particles of dirt, fiber, soot, pollen, paint, food and dead skin. In common parlance, it’s all dust, said Richard Flagan, the chairman of the chemical engineering department at the California Institute of Technology. As soon as these motes lift off a carpet (or a TV remote or a ukulele), "you induce air currents" that propel them around the room, he said.

Several thousand particles of this stuff will waft in any cubic centimeter of air, a space the size of a sugar cube. We travel through life emitting what scientists call “a personal cloud” of dust. The only alternative is death, which is actually worse — what with the whole "ashes to ashes, dust to dust" thing.

A clean house is easier to clean.

How does dust fall onto a bookshelf? Slowly. Very slowly.

A piece of dust that is 100 microns in diameter (the size of a dot of chalk powder) will fall about a foot a second, said Richard Flagan, chairman of the chemical engineering program at the California Institute of Technology. A mote that is 1 micron in diameter, the size of a bacteria, will fall just 30 microns a second. And many of the particles created by cooking, which is a leading source of indoor dust, measure less than half a micron across.

Where does dust this small go? Anywhere it wants. Trying to herd it into a dustpan is either an act of hubris or a clown routine. Might as well try to snare a moth with a hula hoop.

Given these absurdities of scale, cleaning will inevitably scatter dust around the room. Still, the forces of chemistry and physics can help.

There may be no more primitive dusting tool than a damp cloth. You will not see it advertised on late-night TV. But that doesn’t mean it won’t work. "The reason that you use a wet cloth rather than a dry cloth," Dr. Flagan said, "is the liquid introduces capillary forces."

The dust will bond to the wet surface, he said. "And then the particle doesn’t want to pull off."

The concept behind a vacuum cleaner isn’t hard to understand. The nozzle sucks air into a filter medium or a bag. "Some of the dust strikes the filters and sticks, and some strikes other particles and sticks."

Then there is the considerable amount of dust that doesn’t stick to anything. A spinning brush may send small particles in a kind of appliance thrill ride. And while the vacuum nozzle inhales, the vents exhale. A HEPA filter, with its fine fabric grates, should capture petite-yet-nasty particles — the ones that wear size 0, so to speak.

As for those newfangled bagless vacuums with their racy cyclonic action? Dr. Flagan contends that a centrifugal windstorm won’t capture smaller particles, except by dumb luck. That said, on the filth mats that we call carpets, "a lot of the stuff is big aggregates," he said. For that, "they’re pretty good."

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For those who can't get enough of dust, consider this entertaining book: