Strong Decline Near Boston of Solar Aureole Brightness and Column Load of Giant Aerosols.

摘要

Large airborne particles, up to 100 microns in size, which originate from industry and transportation and especially from roads and highways, can nearly always be detected at the edge of the sun's disk due to their strong forward scattering. During May and June, airborne pollen make aureoles sometimes significantly brighter (and colored). In the balance between production, dispersal by turbulence, and fallout, brightness generally increases significantly during the day. By measurably suppressing the glare, it was found, in observations since 1974, that the average brightness, and therefore the column load of giant aerosols, gradually decreased to about one tenth of that in 1979. This is about 8 times faster than reduction in central and eastern sites of pollution measures -- about 4% per year -- related to small-sized haze and smoke. A corresponding, yet small effect can be deduced from high-volume aerosol collections from urban areas in two size ranges. Had those 24-hour and all-weather collections been made in daytime and fair weather only, the results might have confirmed ours more quantitatively. Keywords: Aerosols; Forward scattering; Sky brightness; Dust; Pollen; Solar aureole brightness; Visibility; Air pollution. Reprints. (edc)