Improving the accuracy of charge size distribution measurement using electrical low pressure impactor

Advances in instrumentation have enabled researchers to understand aerosol processes at microscopic levels. Besides the development of instruments, other aspects like its calibration, interpretation of data, long term accuracy are pivotal. The Electrical Low-Pressure Impactor (ELPI) is one such advanced and relatively recent instrument that is used to measure the number and charge size distribution of aerosol particles. The charger toggles automatically for the set-time enabling the software to estimate "size segregated charge per particle" in measurement mode. The current levels become stable only after the transition time of 2-4 s when the charger toggling takes place. The accuracy in the estimation of "charge per particle" depends on the correctness of the omission of the transitory values. In this study, the role of transition time on the software predicted charge per particle was probed quantitatively. This was done for 1% (w/v) NaCl and 1% (w/v) Na2CO3 particles respectively generated via the nebulization process. ELPI + software (ELPI + VI version 2.0) was found to over-predict the charge per particle by a factor of 0.2-4.8. The transitory time used in the software seem to be insufficient and therefore quantitative results of this work will be helpful while performing data analysis.