With-in the realm of air borne particles there are some LAWS that govern their creation, composition and modes of travel.This month we’re going to look at a phenomenon called BROWNIAN MOTION or “random walk”. Small airborne particles, some that never settle & others that settle out in minutes, have a random pattern of travel that they follow (randon walk). When minute particles such as mite carcases, smoke, viruses, bacteria etc are introduced into the environment they immediately begin to bang & bump & knock each other around as they are pushed by the natural air currents & convections with-in the space. Their direction changes constantly and hence the term “ramdom walk”. This, so far, is not amazing nor mystifying, but what is interesting is that all of these particles (whether solid or gas) will continue to bounce and vibrate with-in the confines of the space until the distance between each of them has equaled out. Something like the equalizing of pressure in a tire or a balloon. Imagine the shape a balloon might take if the air molecules inside the balloon did not follow this order and settled out where ever they chose within the balloon. So the dust that settles on furniture and glass surfaces does so evenly across the entire surface, the longer the particles remain air borne the more evenly they will settle on surfaces. The heavier particles (10 microns & up) settle more quickly and their “random walk” is much shorter and they therefore settle out closer to their source. The particles that do not settle out (constantly airborne) will continue their “random walk” until their spacing is perfectly balanced out. This can best be seen with some sort of smoke generator (incence etc.) The smoke particles seem to disappear but in fact they never leave the area. They just bounce around until their spacing is so great they are for all intent and purposes invisable. These particles can move through an environment on currents & eddys in the air and, will rise and fall with the warm & cold convections with-in a space. This explains why if a laser particle counter is taken into a confirned area the lower levels have a smaller count than do upper levels BUT the upper level particles are far more numerous and considerably smaller. This can also occur between floors as well as from floor to ceiling in the same space. Brownian Motion continues to work on these particles and as we move from room to room we redistribute the particles that will hence continue to “walk” to balance out their density. So the fish that you cook in the kitchen at six o’clock (even with the exhaust fan operating) will still be in your second floor bedroom at 10:00pm when you decide to turn in, and those particles will continue to move around in your “residential soup” until fresh air is added while the “stale” air is drawn away and the dillution of the particles leaves the space less contaminated. And even as that occurs the particles are moving with-in that space in a random pattern to “equalize” their density and maintain equal spacing.