THE PLANET'S TERMINAL CONDITION

When white sun light passes through a substance (and it passes through everything if you make the slice sufficiently thin), the sub-stance absorbs selectively: it will transmit only some colors, and reflect or absorb others. Many gases are transparent to all colors of visible light (so we call them "invisible"), but they absorb other parts of the light spectrum, such as infrared or ultraviolet or certain bands of radio waves. For example, oxygen is "invisible," mean-ing transparent to visible light, but it will absorb certain bands of very short radio microwaves. Using a spectroscope one can deter-mine which frequency (color) bands of light are absorbed in a gas or other substance, and which are transmitted.

Of course, the color bands (or "spectra") that get absorbed do make it through the substance if the layer is thin enough. A glass of raspberry juice held against the light is red, but it appears green when held against a strong green light. An aquarium full of it and held against the same green light will make the light darker green, and if one looks through a 10ft pipe filled with the juice, it will probably be black. This is because the absorbed colors are absorbed or weakened ("attenuated") gradually, and only if the path is long enough are they absorbed until nothing (i.e. black) is left.

But clearly making the light path longer merely introduces more juice into it, and since raspberry juice is concentrate mixed with water, I can get the same effects by adding more concentrate to the water; in fact, if I measure the attenuation of the green light, i.e. the ratio of incident to transmitted light, I have a raspberry-juiceometer that tells me how much concentrate there is in the water.

Stedman uses such a juice-ometer, except that he measures carbon dioxide in air rather than juice in water, and that he must therefore use the absorbed color, which is infrared.

Stedman's team has tested over 117,000 vehicles in traffic for CO emissions, and found that 10% or less were responsible for half the pollution.

There is also, of course, a marked dependence on model year. From 1973 to 1989, the percentage of CO in the exhaust dropped from 3% to around 0.1%. This is in agreement with most other parameters showing clearly that the air in US cities is getting ever cleaner, or translated into Econutese, that the conditions for life on this planet are running down.

[More: D. H. Stedman, "Dirty-Car tuneups beat Oxy-Fuels by a mile," Wall St. J., 2/6/90 (available in Fort Freedom); "Automobile carbon monoxide emission," Environ. Sci. & Tech., vol. 23, no 2, 1989; [with others:] "On-road carbon monoxide emission measurement . . .," Environ. Sci. & Tech, vol 24, no 6, 1989; "IR long-path photometry: . . .," Analytical Chemistry, vol 61, 671A (1989)

(this contains the description of the measuring measurement).]