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42.04 APPLICATION FOR PERMIT FOR SURFACE OR DNDERGROUND MINING ACTIVITIES -- <br />MINIMUM REQUIREMENTS FOR INFORMATION ON ENVIRONMENTAL RESOURCES. <br />• <br />2,04.8 Climatological Information. <br />(1) Climatic Characteristics of the North Fork Valley (Cont'd.) <br />(b) and (c) (Cont'd.) <br />light" that causes stars and distance lights to appear <br />"fuzzy", e.g. to lose apparent contrast. <br />The extinction coefficient (bext) is actually the <br />summation of the air and pollutant scattering and ab- <br />sorption interactions: <br />bext - bas + bscat + bans <br />where: bas = scattering by air molecules (Raleigh <br />scattering) <br />bag = absorption by air molecules - usual- <br />ly N02 <br />bscat scattering by particles <br />babs absorption by particles <br />The units of bext are usually km-1 or <br />10-4 mi.-l. As extinction increases, visibili- <br />ty decreases. <br />Visual range, e.g. the distance one can distinguish a <br />target from its background (contrast = 0.02) is often <br />related to the extinction coefficient by the equation: <br />Vr = 3.9 <br />bext <br />Unfortunately, the visual range is very sensitive to <br />incremental changes in aerosols. And also unfortunate- <br />ly, this sensitivity is not linear. The addition of <br />one g/m3 of fine particles to a pristine air mass <br />when the visibility range is 150 miles will reduce it <br />by 30 percent. Addition of the same amount when the <br />background visual range is 20 miles produces a three <br />percent reduction. <br />In the North Fork Valley, the particulate loading is <br />highly variable, but on the average is quite low. The <br />generally small increment added to the background by <br />the Company's activities would not justify the cost of <br />a monitoring program for inversion heights and frequen- <br />cy of occurrence. The regular strong air flow down the <br />canyon at night, plus the widening of the valley below <br />. Revised 10/01/87 <br />65 <br />