Improving the performance of portable aerosol size spectrometers for building dense monitoring networks

Abstract

The ideal particle number size distribution measurement instruments for building dense networks would be compact, easily maintained, and able to produce accurate results. This is challenging to achieve because when reducing the size of size spectrometers, their accuracy is often reduced as well. For existing portable size spectrometers, a large source of uncertainty is unipolar chargers due to their instability in the achieved charge distributions. To address this issue, we modified a set of commercial portable size spectrometer such that its unipolar charger is discarded and it measures charged particles of both polarities, a method that has proven to be efficient in reducing charging-related uncertainty for size spectrometers. We used indoor, outdoor, and NaCl aerosols as test aerosols and compared size distributions obtained using the modified and the original spectrometers with those measured using a set of reference size spectrometer. We demonstrate that size distributions obtained using the modified spectrometer were in better agreement with those obtained using the reference size spectrometer than the original one. By using the new charging method in portable size spectrometers, we improved their performance and reduced their size at the same time, making them a more suitable choice for building dense monitoring networks.