AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Seasonal and Spatial Variability in Oxidative Potential of Quasi-Ultrafine Particles (PM0.25) and its Relation to Water Soluble Metals in the Los Angeles Metropolitan Area
ARIAN SAFFARI, Nancy Daher, Martin Shafer, James Schauer, Constantinos Sioutas, University of Southern California
Abstract Number: 240 Working Group: Aerosol Chemistry
Abstract Seasonal and spatial variation of redox activity of quasi-ultrafine particles (PM0.25) and its association with water soluble metals was investigated at 9 distinct sampling sites across the Los Angeles metropolitan area, including source, urban and/or near freeway and rural receptor locations. High-resolution inductively coupled plasma sector field mass spectrometry (ICP-SFMS) was used to quantify the concentration of trace elements and metals and redox activity was assessed by macrophage reactive oxygen species (ROS) assay. Seasonally, fall and summer displayed higher ROS activity compared to spring and winter. ROS levels were generally higher at source and background sites compared to rural receptor locations, except for summer when elevated ROS levels were observed at rural receptor sites. Univariate linear regression analysis indicated strong association between ROS activity and water soluble transition metals (including Fe, V, Cr, Cd, Ni, Zn, Co, Mn, Mo, Pb, Cu and As). Multivariate regression method was also applied to three site clusters to identify the major drivers of ROS and also to obtain a model to predict the ROS activity of PM0.25 based on its water soluble metal content. The most important drivers of ROS were identified as Cu and La at source Long Beach, Fe and V at urban Los Angeles and Fe, Ni and Zn at Riverside as the rural receptor location. At Long Beach, the best fitted model was able to reconstruct the ROS activity with a high coefficient of determination (0.82). For Los Angeles and Riverside, however, the outputs of multivariate regression could not explain more than 63% and 66% of the ROS, respectively. The unexplained portion of the measured ROS activity is likely attributed to the effect of organic species and secondary organic aerosols (SOA) which were not included in our model.