Aerosol concentrations during the 1999 Fresno exposure studies as functions of size, season, and meterology

Two 1999 Fresno exposure studies took place in February (winter season) and April/May (spring season) for periods of four weeks each. During that time , nearly continuous measurements of outdoor aerosol concentrations were mad e with a TSI Scanning Mobility Particle Sizer (SMPS) and a PMS optical part icle counter (LASX), These instruments provide particle size distribution i nformation from about 0.01 to 3 mum, Although the primary concentration mea surements were performed with integrated samplers, the SMPS/LASX combinatio n provided useful information on the real-time variations of concentration and particle size distributions. This paper describes the agreement between the real-time instrumentation and the integrated measurements and examines some of the information available from the SMPS/LASX combination. In parti cular, two different types of aerosols contributing to PM2.5 were deduced f rom the instrumental data.