Colloquium: Friday, June 1, 1:00 pm, EN6085A

Abstract:

The stratospheric aerosol layer first measured by Junge et al., (1961) extends from the upper tropopause to approximately 35 km. Balloon borne measurements of stratospheric aerosol have been undertaken from Laramie, Wyoming since 1971 making it the longest continuous record of in situ stratospheric aerosol measurements available (Deshler et al., 2003). In this time there have been two different Optical Particle Counters (OPCs) used, providing a long term record of size resolved concentrations at two sizes, 0.30 and 0.50 µm. The current University of Wyoming OPC (UWOPC) which has been in operation since 1989 measures concentrations at 12 sizes including the two historic sizes. The UWOPC is becoming difficult to maintain as spare parts are in short supply, and the light source of the instrument has a relatively short lifetime. A new instrument (PMIOPC), manufactured by Particle Metrics, Inc., has been proposed to replace the UWOPC. The aim of this thesis was to develop, characterize and calibrate the PMIOPC for in situ measurements of the vertical profile of size resolved aerosol concentrations.

The PMIOPC has been modified and tested in the laboratory to enable it to; withstand low pressure and temperatures, size particles at fairly even intervals across the range of the instrument, and dilute ambient aerosol concentrations to below the threshold for coincidence. Four balloon flights took place allowing the comparison of aerosol size distributions and surface area measured by both the UWOPC and PMIOPC. The results so far have been encouraging with similar size distributions, within sampling error, observed by the UWOPC and PMIOPC. Surface area estimates from the PMIOPC generally underestimate those calculated by the UWOPC, but this analysis has only been applied to one flights data. The PMIOPC has proven itself as a good candidate for replacing the UWOPC, but there are still some issues that need to be addressed.