AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Rapid Measurements of Particle Hygroscopic Growth with a Humidity-Controlled Fast Integrated Mobility Spectrometer (HFIMS)
YANG WANG, Tamara Pinterich, Steven Spielman, Susanne Hering, Jian Wang, Brookhaven National Laboratory
Abstract Number: 247 Working Group: Instrumentation and Methods
Abstract Hygroscopicity is a key parameter in determining the impact of atmospheric aerosols on global radiation and climate change. Tandem differential mobility analyzer (TDMA) system is the most widely used instrument for determining the aerosol hygroscopicity. However, TDMA measurements are relatively slow because the time needed for a full scan of DMA voltage is typically in the range of minutes. The slow measurement speed becomes a significant issue when unsteady sources of aerosols are being studied, for example, direct measurement of combustion aerosols and measurement of aerosols onboard mobile platforms.
The recently developed water-based fast integrated mobility spectrometry (WFIMS) allows rapid mobility-based measurement of particle size distribution. It uses a parallel plate mobility system to separate charged particles with different mobilities. Upon exiting the mobility separator, the spatially separated particles are condensationally grown in a three-stage water-based growth channel and imaged onto a CCD array. The size distribution is obtained by counting particles located in each mobility bin shown on the image, providing a near instantaneous measurement (1 Hz) of mobility size distributions. The use of water vapor enables independent control of RH in the mobility separation region, which cannot be achieved with alcohol vapor due to their lower diffusivity. A humidity-controlled FIMS (HFIMS), consisting of a DMA, a relative humidity control unit, and a WFIMS coupled in series, was tested for measuring the hygroscopic growth of particles. In this study, a data inversion algorithm is developed to derive the growth factor distribution of the DMA-classified particles. The inversion algorithm uses the known transfer functions of the upstream DMA and the WFIMS, and calculates the growth factor distribution that reproduces the position distribution of particles measured by the WFIMS. The growth factor distributions of ambient particles at various RHs are analyzed with the inversion algorithm. Further optimization of the HFIMS system will be discussed.