Aerosol Size Distributions At The ASCENT Los Angeles Site: Toward Better Interpretation Of Growth Events And Instrumental Artifacts

VINE BLANKENSHIP, Haroula D. Baliaka, Ryan Ward, Purushottam Kumar, Richard Flagan, California Institute of Technology

     Abstract Number: 124
     Working Group: Urban Aerosols

Abstract
Atmospheric particles have immediate effects on health due to their ability to penetrate deep into the lungs when inhaled. Caltech operates an Atmospheric Science and Chemistry mEasurement NeTwork (ASCENT) field site in Pico Rivera, CA that, like all ASCENT sites,  is equipped with an array of PM2.5 instrumentation.  Size distribution measurements made with a TSI SMPS have revealed events in which particles starting from the smallest particles measured (13 nm in diameter) grow to ~100 nm that are reminiscent of so-called “nucleation bananas.”   These data demonstrate that atmospheric nanoparticle growth is now occurring in the morning, afternoon, and night, likely as a result of changes in the composition of the urban atmosphere over the past decade. These growth events could be the result of nucleation, however nucleation mode particles (Dp  < 10 nm) cannot be detected with our SMPS model. Currently, particles can only be detected once they have grown to sizes larger than the nucleation mode.  An alternate explanation is that ultrafine primary particles emitted from vehicles or other sources, or residues from partial evaporation of larger atmospheric particles may be the seeds for the growing particles. Hence, nucleation can not be confirmed. This challenge has brought forth an opportunity to explore new methods of the analysis and representation of ASCENT size distribution data, which can be applied throughout the ASCENT network and to other atmospheric size distribution data.