Not only is smoke related to the frequency of fogs, but it also increases both the duration and the density of fogs. The water globules become coated with a film of black, sticky, tarry soot which retards evaporation. These soot fogs, or “pea-soup” fogs as they have often been called because of their grimy opacity, may at times become practically impervious to the luminous rays of the sun. Even in one of the lighter varieties of fogs the soot products may increase seven fold. Many average soot-fogs reduce the amount of light one-half. On an exceptionally dark day in Berlin the light was only 1⁄500 of what it was on an ordinary overcast day and only 1⁄3000 to 1⁄4000 of what is was on an entirely clear day (H. H. Kimball). The smoke in the center of Leeds on an ordinary day absorbs as much as 25% of the total daylight as compared with the suburban sections of Leeds, or 40% as compared with the suburb of Garforth, which is 7 miles distant ([4]).
That smoke must materially decrease the limits of visibility is patent from what has been said. The limits of visibility vary with the number of dust particles in the air: 1,000 particles per cu. cm. render large objects like mountains invisible at a distance of 100 miles; 100,000 particles render them invisible 1 mile away, and 1,000,000 particles 1⁄10 of a mile distant (Aitken). Smoke not only fills the atmosphere with countless numbers, but with extremely opaque particles. These particles may unite with globules of water and this makes the atmosphere still more opaque. As was stated above, in large cities even in fine weather there may be over 300,000 particles per cu. cm., as against a few hundred in the country. Accordingly, we find in London that the limit of visibility in the winter time, even during the clear part of the day, does not exceed one-half mile.
The temperature readings are somewhat unsatisfactory because they usually include only the maximum and minimum records for each day. Minimum temperatures are found to be perceptibly higher in the cities than in the country, partly because of city heat, but chiefly because the smoke blankets prevent the escape of the heat at night. In Pittsburgh the minimum temperature averages about 4° higher than the temperature in the adjacent stations (Kimball). In the day time the upper surface of the smoke clouds absorbs portions of the sun’s heat, and this inevitably lessens the heat on the ground surface. The solar energy has been reduced 40% by smoke clouds ([12]), and it is possible that very little heat penetrates to the earth’s surface during a very dense smoke cloud. In London the surface temperature during a given reading was 44° F., while 59 ft. directly above it was 51.5°, a difference of 7.5°. Between 9 A. M. and 3 P. M. the surface temperature rose 7.5°, while the roof reading rose 16.5°, or more than twice as much. Although thoroughly satisfactory data are not available it is undoubted that smoke (which is most abundant in the atmosphere in the winter time, owing to lessened convection) lowers very perceptibly the diurnal winter temperature in smoke-producing cities.
Finally, smoke indirectly affects the electrical potential of the atmosphere. I know of no direct study of this question, but it is possible that smoke causes a decrease in the potential because it tends to increase humidity. An increase of humidity decreases the potential (save possibly during fogs, as noted later, [14]). We are also told that the potential increases with the turbidity (Trubung) of the atmosphere, and consequently with high barometric pressure. Since smoke tends to decrease the diurnal temperature, particularly in the winter time, it apparently tends to increase the diurnal potential, as the potential decreases with increasing temperature ([14]).
Having thus discussed the atmospheric changes caused by smoke we now turn to the second question. How do the various smoke-induced weather states affect the mental and bodily health and happiness of human beings? It is evident that the problem can be formulated largely in terms of sunshine dynamics. On the one hand, we have the psychic and physiological influences of positive states of sunshine: brightness, luminosity, warmth, dryness, the presence of the infra-red, spectral and ultra-violet rays, and high electrical potential (because of dryness). On the other hand, we have the effects of the negative states: gloom, darkness, cloudiness, fogginess, rain, moisture, cold and low electrical potential. It is utterly impossible to separate all of these components, and it will, therefore, be no easy task to measure the influences of each component.
Literature, both poetry and prose, contains frequent allusions to the alleged effects of sunshine or the absence of sunshine on the feelings of man. Charles Lamb “felt himself immortal” and “a great deal taller” on bright days. Moore took delight in sitting in the sunshine:
“Blessed power of sunshine! genial day,
What balm, what life are in thy way!
To feel thee is such real bliss,
That, had the world no joy but this,
To sit in sunshine calm and sweet,
It were a world too exquisite
For man to leave it for the gloom,
The deep cold shadow of the tomb.”
Byron felt “more religious on a sunshiny day,” Pope refers to “the soul’s calm sunshine,” Rousseau sat with bared head in the sun; Shelley so coveted the most intense sunlight that he did his writing from the roof, while it is a common observation that people generally, and particularly the aged, instinctively seek the sunshine. Mrs. Hemans wrote a rapturous apostrophe to the sunbeam:
“The sunbeam of summer
O! what is like thee;
Hope of the wilderness,
Joy of the sea.”
Many writers cannot do satisfactory work unless the weather fits the mood, motive or scene; unfavorable weather states cause a disagreement in the thought processes([27]).