Combination coefficients of small ions with aerosol particles

Abstract

This work was concerned with the measurement of the variation of the combination coefficient between aerosol particles and small ions, b, with the radius of the particles. The variation of the combination coefficient between uncharged aerosol particles and small ions, ɳo, with radius was also examined. The ion-ion recombination coefficient,ɤ, was first evaluated from plots of small ion decay in an aerosol-free mylar vessel of volume 3.1 m(^3). Small ions were produced from corona discharge around the tip of a steel needle, set at a high voltage. 14 measurements of were made, giving a mean experimental value of 2.39 (-0.14) x l0(^-6)cm(^3)sec(^-l). A technique was developed for simultaneous measurements of the ,combination coefficient b and the aerosol particle size. Particles were produced by blowing filtered air over a glowing nichrome wire. Methods of number concentration and particle size determination are described. The decay of the ions in the presence of the particles in the mylar vessel was recorded and compared with a family of theoretical ion-aerosol decay curves plotted by the computer to determine b. A total of 26 b measurements were made and the value ranged from 0.35 x 10(^-6)cm(^3)sec(^-1) to 2.24 x 10(^-6)cm(^3)sec(^-1),corresponding to radii of 0.41 x 10(^-6)cm to 4.0 x 10(^-6) cm. The variation of ɳo with radius was also investigated in ten of these b measurement experiments. The value of ɳo ranged from 0.33 x l0(^-6)cm(^3)sec(^-1) to 2.39 x l0(^-6)cm(^3)sec(^-1) for corresponding radii of 1.26 x l0(^-6)cm and 4.0 x 10(^-6)cm. Various theoretical models for combination coefficients were discussed. The b and ɳo versus radius results were compared with theoretically computed values. The discrepancy between the generally larger experimental values and theoretical values for the combination coefficients was also discussed.