Document nKOEw7Z9E5ONqwenK2Xk5MmG

December 16, 1954 Mr. Robert D. MacPhee, Chemical Engineer Air Pollution Control District County of Los ,,uigeles 5201 Santa Fe Avenue Los Angeles 5 8 # California Dear Mr. MacPh.ee: "'hank you for your letter of December 7 in reply to my letter of November 24, add.roaa.ed to Mr Gordon P. Larson. I am in general agreement: with your comments concerning the concentrations of lead which one can expect to find in the atmosphere. The concentrations of 4? and j4 micrograms lead/M3 , however, are so unusual that they must be considered as spurious results. Fo r the record, it might be of interest to note that the value of 14 micrograms/M.3, which you quote from Dr. F p t e r 's report, is from our analysis of materials collected in a co-operative investigation by the Laboratory and the U. 2-. Public Health Service : . \ '. . As you no doubt knbw, we have been determining for SCAPF, among other pollutants, the concentrations of lead in the suspended matter of the Los Angeles area. We have analyzed, gpectrographically, 100 consecutive large volume samples (24-hour) collected at each of two stations in the area during the recent, inversion season (August 9 through November 19) In addition to the 2-'-i-hour large volume samples, we have collected hourly filter paper spot samples in a continuous 2^1-hour program at the same two stations and have completed at this writing the analysis of about 8 0 0 samples, each of which correspends to a collection period of two hours This part of the program was designed to obtain information concerning peak concentrations of lead which can occur at different hours of the day as a result of changes in the meteorological conditions and in the pattern of the motor traffic. These samples were analyzed by a very sensitive and precise dithizone method. The ranges of concentration of lead on the 24-hour high volume samples for the 100 day period were: Station #5 (bos Angeles) #4 (Pasadena ) Micrograms Pb/M3 1.4-14.3 1 . 1- 12.8 Mr. Robert D* MacPhee, December 16# 195^ 2- The average concentrations have not been calculated for the full 100 day period, hut Inspect Ion of the data indicates that the daily average concentration for Station #3 will he between 5 and 7*5 aicrograma lead/?!3 , and between 5 and 5 micrograma lead/M3 for Station 4. In the case of the spot filter caper samples, the ranges of the load concentration ares Station #3, <^0.5-16.9 micrograms lead/M3 and Station (0*5-12 micrograms lead/M3 . We feel .that the single high'value given in your report, and the micrograms/M3, reported in your letter, are so far beyond the upper limits of the ranges of concentration which have been found by us and others In continuous studies of Los Angeles and other American communities that they would undoubtedly be discarded in any statistical analysis of the aata. It w a s 'unfortunate that the isolated high result of 42 micrograms/M3 was included In your report, since this is likely to lead to seme bizarre interpretations of the finding. r"he query concerning the 150 raierograms lead/M3 was prompted by a oaragraoh in Consumers 1 Research Bulletin, for- August 1954*" where it was stated: rt0HE OP 1 KB CTi '1 HEALTH PICSLEMS 1 contaminated air In two cities where studies are being made, paper filters coated with samples of air pollutants show that at rush hours the lead content from automobile exhausts Is near the limit of human tolerance/1 r7M s Is in complete variance with our data which show peak concentrations of approximately 1/10 of the accepted threshold limit. Our experience in other coaimuni-feies indicate that this finding is not peculiar to Los Angeles, and that the average concentration of lead which one can expect to find In the atmosphere of most large American cities will fall between 1/75 and 1/ 3 0 of the threshold limit (2-5 lalerograms lead/M3 ). i have quoted the paragraph from the Bulletin in ease It has escaped your notice, and also In the hope that if you were aware of itv.# T ou might be able to shed some light on the work which led to the statement Best regards for the Holiday Season and the Hew fear. Very truly yours, T7TMChoIaE JC :ma cc Mr.; Gordon P . Larson Dr. R , A . Kehoe ) Omitted from Mr* Mr:. J . B . MacCauleyj Larson's copy.