AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
High Speed Size Distribution Measurements of Aerosol Particles
Michael Pikridas, Chongai Kuang, Steven Spielman, Susanne Hering, JIAN WANG, Brookhaven National Laboratory
Abstract Number: 88 Working Group: Instrumentation and Methods
Abstract A Fast Integrated Mobility Spectrometer (FIMS) was developed for rapid measurements of aerosol size distributions from 10 to 450 nm. The FIMS consists of a classifier, a condenser, and a detector (Kulkarni & Wang, 2006, J. Aerosol Sci.). Inside the classifier an electric field separates charged particles onto different flow lines, based on their electrical mobilities. The strength of the electrical field varies spatially by over three orders of magnitude, such that particles of a wide range of electrical mobilities can be simultaneously separated (Wang, 2009, J. Aerosol Sci.). The separated particles are then carried by a butanol-saturated sheath flow into the condenser, where a supersaturation of butanol is generated through electrical cooling and the classified particles grow into super-micrometer droplets. At the exit of the condenser, a laser sheet illuminates the grown droplets, and their images are captured by a CCD camera. The images provide both particle concentration and position, which directly relates to the particle electrical mobility. By simultaneously measuring particles of different sizes, the FIMS provides aerosol size spectra at a time resolution of 1 Hz, nearly 100 times faster than traditional SMPS. The sizing accuracy of the FIMS was characterized by measuring monodispersed aerosol classified by DMA over the size range of 10 to 450 nm. The results show that the FIMS measures the particle size accurately, and has a nearly 100% activation efficiency for particles as small as 10 nm.
Recent deployment onboard research aircraft demonstrated that the FIMS is capable of measuring aerosol size distribution spectrum in 1s, thereby offering a great advantage over SMPS in applications requiring high time resolution. In addition, FIMS could also improve the time resolution of other measurements relying on scanning mobility technique, such as aerosol hygroscopicity using Tandem DMAs. A system employing water-condensation technique is currently being developed.