The new air world

by Willis L. Moore

Ozone has two daily maxima, the principal one occurring between 4 and 9 A.M. The minima occur between 10 A.M. and 1 P.M., and between 10 P.M. and midnight. The winter furnishes an amount greatly in excess of the summer, due not only to the less amount of decaying matter to take up the ozone in winter, but to the higher and more persistent winds mixing the lower and upper air. The amount is greater over the sea than over the land, probably due to the absence of oxidizable matter, which allows the ozone to accumulate over the water. It is more abundant with westerly than with easterly winds, due to the fact that westerly winds have a downward component of motion; but if the westerly winds be weak and the easterly winds come from over a large body of water the conditions may be reversed.

Microbes of the Air. The air transports vast armies of unseen workers. Some are enemies; others are benefactors of the human family. The useful varieties are energetic in clearing away the refuse of animal and vegetable life, in fixing fertilizing gases in the soil, in giving flavor to fruits and proper growth to leguminous crops, in transforming the crudest must into the best claret, and the poorest tobacco leaf into the fragrant Havana; in curing cheese and butter and fermenting beer, and in a multitude of other useful employments. The malevolent varieties, if they gain lodgment in suitable human tissues before sunlight weakens their virility, disseminate certain forms of disease.

In picking a permanent place of abode, remember that there are many less disease microbes in the air of the open country than in that of the city, and that few are found in the air of mountains, or in that of the ocean. The average number of bacteria in a cubic meter of air in the city of Paris has been found to be 4790, while ten miles away in the country the number was only 345.

Accurate analyses of the air of crowded tenements always have shown large numbers of bacteria, but the number was found to be small in well-ventilated city houses that let in an abundance of sunshine to their interiors. It is better to have color in the cheeks of the occupants than in the furnishings of a house. Curtains and heavy drapery not only furnish a refuge for the microbes of disease, but they may be so hung as to exclude the purifying sunshine. The amount of sunshine is nearly as important as the quantity of air, for most of the microbes of disease quickly die, or are rendered less virulent, under its influence.

Bacteria exist in small numbers, if at all, at altitudes where snow forms, but snow gathers them as it falls through the lower air. Ice contains bacteria, but not in any such quantity as the water from which it freezes. Ice forms in the open at the surface of the water, or about numerous small particles of matter in suspension, which rise at once to the top as soon as the ice congeals about them in the form of a buoyant covering; meanwhile sediment is continually settling to the bottom, carrying bacteria with it. Ice forms more readily in quiet water, where sedimentation has been most rapid, and where, therefore, there are the fewest bacteria in position to be included. More disease germs exist in river water in winter than in summer, which may be due to the greater disinfecting power of the sun’s rays during summer.

Dust Motes of the Air. As the earth pursues its course about the sun, dust rains into its atmosphere from outer space. Meteors that are burned through the heat generated by striking into our air contribute to the supply, as do volcanoes, combustion, spray from the ocean, and matter lifted up by the action of the wind.

Dust from the eruption of Krakatoa was wafted entirely around the earth, falling upon the decks of ships in all the seas of the world. It affected the colors of the sky for two or three years after the explosion.

As in the case of microbes, the number of dust particles is far greater in cities than in the country, being least on high mountain tops and over the oceans. The air in large cities invariably shows hundreds of thousands of dust motes to the cubic centimeter, that of the village thousands, and that of the open country some hundreds. Dust-free air is also germ-free. Many experiments have shown that air freed of dust motes has at the same time been cleared of the microörganisms that cause disease, putrefaction, and fermentation; and that germ-free flesh or liquids may be indefinitely exposed in such air without fermentation or decay.

How Dust Motes Are Counted. Many of the particles are too small to be seen by the highest powers of the microscope, yet Aitken, by a most ingenious method of making them centers of condensation—that is, making them the nuclei of small raindrops—was able to count the number in a given volume of air. When ordinary air is saturated and then cooled the cloud formed is so dense that it is impossible to count the tiny droplets that form the cloud. But we can make the number of dust particles (and therefore the number of visible points of condensation) in a given volume of air as small as we wish by mixing a little dusty air with a large amount of dustless air, and we can allow the particles to fall on a bright surface and can count them by means of a lens or microscope. By simply allowing for the proportion of the dustless to the dusty air, and making a corresponding allowance for the dilution, we calculate the number of particles.

Dust Motes and Illumination of the Atmosphere. One of the most important functions of dust motes is the diffusion or scattering of sunlight. What a different world this would be without these tiny inanimate friends of man! If there were no dust in suspension in the air, nothing would be visible except what received direct light, or light reflected from some illuminated surface, and the air occupying space between illuminated objects would be practically dark. If the observer be in a room with a powerful electric light he would see the walls and the objects in the room, but if the air were free of dust motes, he would find that the space between him and the walls and between the various objects would be as inky black as is the space between the twinkling stars on a clear night.