Size distribution of sub micron atmospheric particles by DMA

A Differential Mobility Analyzer (DMA) has been installed at the Department of Mechanical and Civil Engineering at the University of Modena and Reggio-Emilia. The instrument allows automated and continuous measurement of number concentration of air suspended particulate matter within an electrical mobility diameter range of 10 to 800 nm. The DMA has been assembled at the Université Blaise Pascal in Clermont-Ferrand, France. The instrument is capable of operating in a scanning mode as a Scanning Mobility Particle Sizer (SMPS) and in stepwise mode as a Differential Mobility Particle Sizer (DMPS). In the SMPS mode measurements are completed in 2 minutes, whereas in DMPS mode, it takes about 10-12 minutes to complete a measurement over the complete diameter range. For this first testing period (March to May 2007) the DMA have been set up at a height of ~9m above the ground in the Faculty of Engineering building; the inlet have been equipped with a PM1 cyclone, stretched 1 m outside the window and shared with a TEOM instrument. Total particle number concentration and number size distribution spectra observed from March 19th to March 21st 2007 and from April 22nd to April 23rd 2007 are analysed in detail. Hourly variation of total particle concentration for the complete sampling period has been studied. Generally, concentration peaks resulted associated with rush hour during morning and with local meteorological conditions during evenings.