Document KJ8NxnbgvQLa7L5zyqkGLxgLr

Gordon P. Larson Director COPY County of Los Angelos Air Pollution Control District 5201 Santa Foilvenue Los Angeles 58 ' December 7 195^1- Dr. T. Cholak Associate Professor of Industrial Health .lettering Laboratory College of Medicine Eden Avenue - Cincinnati .19, Ohio . Dear Dr. Cholak: In your letter of November 21}.*' 195U* you inquired about the atmospheric lead values in the Second Technical and Administration Report. The footnote in our Table VIII was in error., Lead was measured on carbonised filter papers by arc spectrograph. Standards containing 'comparable' -amounts of lead nitrate (aqueous) on a blank filter* were used. In addition, an internal spactrographic standard of .010 ml. of 20 por cent Lia C0S dissolved in HC1 was used with each filter analyzed. The HC1 was added to decompose the carbonate, during drying and carbonising. An Applied Research Laboratory, l-i/2 meter, grating spectrograph, A.R.L. source unit, platform electrode and densitometer were employed. From they.." numerous samples and standards measured,, it was estimated that results were accurate to within about 10 per cent of the value obtained' ' .' ' . .; , '' It is very possible that the: value of i}2y^gia./M quoted In our report was high, yet we measured m.yma on a later occasion. Seldom does the value exceed 10V^gm./m even during smog attacks. It is interesting to note thafc^ M. J. Fofcer of the'.Environmental- Health Center measured li^.x'^gm./m in one of several samples which we collected for him early this year. In regard to the values in excess of 1yoS4?gm./m3 which , you mentioned In your letter, we do not know where these originated. ; '\ /. . . . . If you have any further questions, please feel free to contact us. Very truly yours, Gordon P. Larson, Director By: /s/ Robert D. MacPhee Chemical Engineer