Real-time size-distributed measurement of aerosol mass concentration

Poster PDF

Description

This report covers research conducted under DOE sponsorship pertaining to atmospheric aerosols that play an important role in climate change. The creation, presence, and decay of particles in the atmosphere determine cloud formation as well as penetration of solar radiation through the atmosphere. Accurate data of atmospheric aerosols are needed to predict global warming and climate change.

This project has been concerned with the development of instrumentation for airplane-based aerosol measurements. As a starting point, we have used our state-of-the-art aerosol sampling instrument known as the micro-orifice uniform deposition impactor (MOUDI). This instrument consists of multiple stages, and at each stage, aerosols of a certain size class are deposited on an impaction plate. Aerosol size ranges from 10 nanometers (very fine) to 10 microns (very coarse). When used aboard an aerial vehicle, the MOUDI allows determination of accumulated aerosol masses in each size class for the entire flight trajectory, because the aerosol mass is determined through laboratory analysis on the ground. Detailed information such as differences between the aerosol size distribution near and far from a cloud and the effect of altitude on the aerosol size distribution is not available. Hence, the objective of the present research has been to investigate the feasibility of sensor technologies that would enable real-time mass measurements at each stage of a MOUDI-type instrument.

The desired sensor technology has now been proven in our Phase I laboratory work. Impedance-based quartz crystal microbalance (IQCM) is shown to be compatible with the individual aerosol collection stages of the MOUDI and would meet the real-time measurement need of the atmospheric research program. The gold disc in the accompanying image is an IQCM sensor mounted to a MOUDI stage, with white dots representing the deposited aerosols. Impedance versus frequency curve of the sensor has two characteristic frequencies (fs and fp), which vary linearly with the mass of the deposited aerosols. The IQCM sensors provide stable output with nanogram resolution.

In the next phase of this project, this technology will be used to develop and deliver flight-worthy aerosol measuring instruments, where aerosol mass would be monitored in real-time for each size class. Further, accessories will be provided to measure the moisture uptake and the deliquescence and efflorescence relative humidity values of the collected samples during the flight.