Single particle perspective on the Southern California Ozone Study: Characterization and evolution of ambient aerosols by aerosol time-of-flight mass spectrometry (ATOFMS)

Atmospheric aerosols play a vital role in global and regional pollution processes that decrease visibility, transport pollution, adversely affect human health, and alter the climate. One way to effectively understand and regulate air quality is by using atmospheric chemistry models. These models, however, are only as good as the information used to create them. One area of the models that requires improvement is the characterization of particulate matter.; As part of the 1997 Southern California Ozone Study-North American Research Strategy for Tropospheric Ozone study (SCOS97-NARSTO), aerosol time-of-flight mass spectrometry (ATOFMS) instruments were used to characterize individual particle size and composition in real-time in the Los Angeles region where some of the highest particulate matter levels in the United States have been recorded. With the use of a newly developed database (YAADA) and a neural network (ART-2a), ATOFMS data reveal the particle types present with high time resolution, in contrast to the time-averaged, bulk properties of the particles sampled using conventional filter-based methods. The real time nature of the ATOFMS data allow for the flexible binning of data to the desired time resolution and, similarly, the single-particle sizing allows for the flexible binning to the desired size ranges when analyzed, even years later. This study allowed for the spatial characterization of aerosols in near-coastal, mid-region, and interior locations in southern California by ATOFMS with previously unprecedented detail and resolution, including for the first time the use of transportable instruments to obtain positive- and negative-ion mass spectra from the same particle.; The data from this study allowed for the comparison of the ATOFMS data with other measurements (including ozone and visibility), the observation of particle transformation between sampling sites, the determination of several-week-long trends in single-particle composition, the continued development of detection efficiency calibration functions for the ATOFMS instruments, and the demonstration and testing of new data analysis approaches for source apportionment. With the exception of the Riverside location, the SCOS97-NARSTO results are the only real-time single particle mass spectrometer data ever acquired at these sites and among only a handful of such data that has information on site-to-site particle transport.