Data reduction methods for the electrical aerosol analyzer (EAA) and the diffusion battery+condensation nuclei counter (DB+CNC) are presented. Both the EAA and DB+CNC can be modeled by the Fredholm Integral Equation of the First Kind. Thus, the data reduction methods for both the instruments are similar. The data reduction methods for both the instruments were analyzed with simulated and experimental data. For the EAA, the comparison between the different data reduction methods for the number distribution is excellent. The agreement between the number distribution retrieved by the three data reduction methods for the DB+CNC was found to be good. Finally, it was shown that for large number mean diameters, the response of the diffusion battery does not change significantly with a considerable change in the dispersion parameter, sigma(g). Thus, the resolution of sigma(g) with the diffusion battery is poor.