APPENDIX B ESTIMATE OF COLLECTION EFFICIENCY OF FILTERS USED IN| AIRCRAFT Filter papers were placed in series during two flights. If we assume t filters do not significantly discriminate according to particle size, t efficiency can be estimated as follows. Let R = fraction of activity retained on filter Cc = Activity in volume of air sampled A, and Ay = Activity collected by first and second filters respectively Then A, = RC Ay = (1-R)R Ro =1- 22 Al The following data were obtained: November 30, 1953 First filter in series Secom filter in series 780 d/min 60 d/min Rwil - 60 780 = 92 December 15, 1953 First filter in series Second filter in series R21 - 40 2070 = 095 59= 2070 d/min 140 d/min