LETTERS
Photochemical smog Dear Sir: I wish to call attention to a potential hazard in controlling photochemical smog by reducing hydrocarbon (HC) emissions without a corresponding reduction in the emissions of the oxides of nitrogen (NO,). If HC concentrations are reduced to keep hourly oxidant levels below the EPA ambient air quality standard of 80 ppb, and if NO, concentrations are not correspondingly reduced, then on many days all the NO will not be oxidized. In the presence of NO, ozone levels are always considerably below the normal background level of 25 ppb, because of the rapid reaction between NO and 03. Thus on the days that NO is not completely oxidized, ozone levels will be considerably below background levels. If many such days should occur in succession, the bacteria count might increase, and this might enhance the incidence of disease (e.g., streptococcus
salivarius shows 90% mortality when exposed to 25 ppb O3 at 60-80% relative humidity for 30 minutes). Automobiles account for a greater percentage of the photochemically active HC than of the NO,. (In Los Angeles it is about 90% for photochemically active HC vs. 70% for NO,). However, the control devices presently being installed on cars are designed to control 80% of the HC and 40% of the NO,. As a result the percentage reduction in photochemically active HC should be about 2-3 times as great as the percentage reduction in NO,. This may not be a policy of wisdom. Julian Heicklen, Professor of Chemistry
The Pennsylvania State University University Park, Pa. 16802 Remote sensing Dear Sir: Since the August 1975 issue of €SAT contained two lengthy articles (pp 714-725) on remote sens-
ing and its growing application to environmental monitoring and assessment, it seems appropriate to bring the services of the EROS Data Center to the attention of your readers. The EROS program was established by the Department of the Interior in 1966 as a departmental effort. The U.S. Geological Survey manages this program. Initial funding for the EROS Data Center occurred in 1971 and Data Center personnel moved into the permanent facility in January 1974. The Center's primary responsibilities are to archive, reproduce, and distribute copies of remotely sensed photographic imagery and electronic data of the Earth's resources, and to provide a variety of professional services to further the understanding and use of these data. The Center serves as an active archival library; a photographic processing facility; a user services facility to assist in ordering data; an applications
organic alysis. aytheon's 2610 Total Organic Carbon Analyzer.
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Environmental Science & Technology
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