(HP-97) Mass Median Diameter

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An extract from Metal Composition and Size Distribution of Atmospheric Particulate Matter In Remote Northeaster Minnesota, University of Minnesota, Environmental Engineering Program, APR 1978

"INTRODUCTION
The work described here details the size distribution of selected metals in atmospheric particulates as related to seasonal and geographical variations and dry deposition.
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APPENDIX B
Mass Median Diameter Calculation
For an aerosol distribution, mass median diameter is defined as the particle diameter usually reported in μm, at which half of the aerosol mass is found on particles of diameter greater than the mmd and half on particles less than the mmd. Mass median diameters were calculated with the aid of a Hewlett-Packard (HP-97) desk-top calculator utilizing the program on the following page. The program was developed by combining and modifying linear regression and inverse normal integral programs supplied with the HP-25 hand calculator. To calculate mmd, the number of stages is input into the HP-97 calculator, followed by the metal concentration of each stage, beginning with the back-up filter. The fraction of mass below each size cut-off is calculated and converted to probability units; both are printed out. The probability units and corresponding size cut-off (log diameter) are input into the calculator in pairs until all stages have been entered. The points will be fit to a line by linear regression analysis, and the slope, correlation coefficient (r²), and mmd will be printed out. A sample calculation is shown on page B-4."
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