LETTERS
PhiIips
PW9790 Darticulates OM a continuous basis. (mass concentration in ;f.gr/m3) Philips new particulate m on it o r, PW9790, measures mass concentration in pgr/m3.
Provides real time information on schedule: Y2 hr. 1 hr, etc.,as you require. Total loading or respirable fraction measurement. Dynamic calibration provided via a mass standard. No weighing of filter papers. No zero drift. Field effective, PW9790 measurements are based on beta absorption technique widely used in industrial application. Expect a new level of effectiveness in environmental quality management when you talk to Philips. Call today (914-664-4500) or write for full data on the PW9790 Particulate Monitor.
Water analyses
Dear Sir: The Federal Water Pollution Control Act, P.L. 92-500, specifies legally acceptable methods for wastewater analysis. Analysis for cyanide is done according to the method outlined in "Standard Methods for the Examination of Water and Wastewater." Mercuric chloride is used in this method to decompose complex cyanides. The Illinois Pollution Control Board has established Water Quality Standards that limit mercury to 0.0005 ppm in any effluent; yet, NPDES permit holders are required to submit daily analysis reports on their effluent. Unless the permit holder has an effluent in excess of 250,000 gal a day, he will be in violation of the mercury limit if he runs a single determination. Does all this mean that in 1985 when EPA demands zero pollution, there will be no more chemical analysis? Arthur G. Janssen, Environmental Engineer Illinois Tool Works, Inc. Chicago, Ill. 60631
ozone layer is destroyed. These two items, however, do emphasize the complexity of the chemistry of the atmosphere, and warn against the oversimplifications that have led to scare stories in the newspapers and lawsuits in the courts. One aspect of the ozone story that I have not seen discussed in either the technical or lay press has to do with what would happen to the excess uv light which would pass through the fluorocarbon-depleted ozone layer. I t is well known that oxygen reacts to form ozone when excited by uv light. Would not the ozone that is destroyed in the stratosphere then be regenerated at some lower level in the atmosphere where the oxygen concentration is higher? In other words, I am suggesting that the limiting factor determining the ozone concentration in the upper atmosphere is the amount of uv radiation penetrating it. I f some of the ozone is destroyed by some mechanism, allowing more uv to penetrate, then more ozone will be generated at lower levels, but the net amount of uv penetrating to the Earths' surface will not be greatly affected.
Smog, ozone, etc.
Gerald A. Gordon
Dear Sir: Two items on your Currents page in the January 1975 issue have stimulated me to write this letter. The first reports that smog decreases the amount of ultraviolet (uv) radiation received by the population by as much as 35%. The second refers to the widely publicized speculation that fluorocarbons may catalyze depletion of the ozone layer in the stratosphere resulting in greater penetration of uv to the Earth's surface. I am not trying to suggest that we should keep the smog to protect ourselves from skin cancer after the
Skokie, Ill. 60076 VC monitor-correction
Dear Sir: In the Feb. issue (p 165), it states that our Personnel Monitoring System can measure individual worker exposure to vinyl chloride at "50 ppm" (parts per million). The minimum detectable sensitivity of this system is actually 50 ppb (parts per billion). The sensitivity is a major advantage of our system. L. F. Millett, Director of Marketing The Bendix Corp. Ronceverte, W. Va. 24970
A North American Philips Co. 750 South Fulton Avenue Mount Vernon NY 10550
CIRCLE 2 6 ON READER SERVICE CARD
Volume 9, Number 4 , April 1975
289
