AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Long-Term Evaluation and Source Apportionment of Redox-Active Metals Using a Novel Metal Monitor and PMF
AMIRHOSEIN MOUSAVI, Mohammad Sowlat, Constantinos Sioutas, University of Southern California
Abstract Number: 34 Working Group: Source Apportionment
Abstract In this study, we measured the concentrations and diurnal variations of four important redox-active metals (i.e., Fe, Mn, Cr, and Cu) using a previously developed metal monitor with a time resolution of 2 hr in both warm and winter phases in central Los Angeles. Positive Matrix Factorization (PMF) model (ver. 5.0) was employed for source apportionment of the concentrations of metals and PM2.5 mass following the approach by Masiol et al.(2017). We also used several auxiliary variables to help better identify the factors resolved by the model. The most plausible solution of the PMF model was the 4-factor solution for the metals data and the 5-factor solution for the particle size distribution data, with the factors being nucleation, traffic, urban background aerosol, secondary aerosol, and soil/road dust.
As results demonstrate, soil/road dust factor has the highest contribution (i.e., 34%) to the PM2.5 mass, followed by traffic and secondary aerosol factors. The major contributor to the concentrations of Fe was traffic (54%), besides urban background with 22% contribution. Moreover, traffic factor was also the major source of Cu, making up to 56% of Cu concentrations. Furthermore, the diurnal variations of Fe and Cu concentrations, indicating peaks during morning and late afternoon/early evening traffic rush hours suggested the major influence of vehicular emissions for Cu and Fe. Urban background aerosol majorly contributed to Cr concentration (58%), which could be attributed to Cr plating facilities and other small local sources in the area. Mn, on the other hand, mostly comes from the urban background and soil/road dust factors, indicating the impact of wear debris tracers from vehicular traffic. Finally, average metal concentrations are higher in the cold phase than in the warm phase, which can be attributed to lower temperatures and depression in the mixing height.