Blue Haze
As the summer traveler goes south from Alaska and northwestern Canada, one of the most noticeable changes is the deterioration in air quality and seeing ability. No longer do distant mountain ranges stand out clearly--one may be lucky to see them at all.
As the sky seems to close in around him, the northerner may sense a loss of freedom. Do Americans not realize how bad their summer skies are? Why don't they stop pouring pollutants into them?
Actually, most of the obscuring haze in the air is quite natural. It would be there whether or not people lived in the area. At least this is true of the blue haze.
Blue haze is densest in forested regions. The haze consists mainly of organic particles in the air. Called aerosols, these particles are bigger than simple molecules, but they are light enough to float in air for a long time. Organic aerosols are those built up of compounds containing hydrocarbons, that is, hydrogen and carbon.
It is thought that the hydrogen and carbon boils off in vapor form from plants and trees. Shining of the sun's rays onto the emitted hydrocarbon vapors causes them to interact with each other and with other naturally occurring elements to build larger particles. As they grow in size, these aerosol particles become large enough to scatter light. Blue light is most easily scattered--hence one sees blue haze. Worldwide, it is estimated that the amount of natural organic haze is 5 to 500 times greater than man- made haze. Of course, near industrial areas, the man-made part can easily exceed the natural component.
The reason we have much less blue haze at high latitudes evidently is that our low summer temperatures do not yield a high rate of boiling off of organic vapors from vegetation. Also, the low sun angle helps to shield out the ultraviolet component of sunlight that causes the vapors to form into aerosols. In coastal regions where there is frequent rainfall, both natural and man-made organic aerosols are washed out of the air since the aerosols are water soluble.
Attesting to the relative permanence of the blue haze in forested temperate regions are several geographic names: the Blue Ridge Mountains of West Virginia, the Great Smoky Mountains of North Carolina and Tennessee, and the Blue Mountains of Oregon and Washington. These names were given long before industrial pollutants existed.
