Ambient single particle analysis in Riverside, California by aerosol time-of-flight mass spectrometry during the SCOS97-NARSTO

Abstract

Single-particle measurements were made using aerosol time-of-flight mass spectrometry (ATOFMS) instruments in conjunction with the 1997 Southern California Ozone Study-North American Research Strategy for Tropospheric Ozone (SCOS97-NARSTO). The size and chemical composition of individual ambient particles in Riverside, CA during the summer of 1997 are described. Data collected using co-located micro-orifice uniform deposit impactors (MOUDI) impactors are used to scale the ATOFMS number counts, providing a unique picture of the particle population which complements information obtained using traditional sizing and composition analysis techniques in this and previous studies. Changes in single particle composition are observed over time, and compared and contrasted with observed changes in visibility, ozone, and PM_(10) concentrations. Details are provided on changes in the particle size and composition observed during three morning periods with low ozone and elevated PM_(10) versus three afternoon periods with both elevated ozone and PM_(10) levels between 21–23 August 1997. The ATOFMS size profiles show afternoon periods dominated by sub-μm particles composed of organic carbon coupled with ammonium nitrate, and morning periods with relatively high levels of super-μm dust particles. The observed changes in particle size and composition are consistent with differences in air mass trajectories arriving at Riverside during the morning and afternoon time periods. Temporal variations in single particle types detected over a 40 day sampling period are presented, demonstrating the type of unique information that can be obtained regarding atmospheric particle processes through long term sampling studies. The broader availability of single particle mass spectrometers coupled with recent advances in the field are now providing unique information on the associations of multiple chemical species (i.e. mixing state) within individual particles with high size and temporal resolution.