AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Trace Metals in Aging Urban Particulate Matter
JOSEPH SALAZAR, David Pfotenhauer, Frank Leresche, Fernando Rosario-Ortiz, Michael Hannigan, Brian Majestic, University of Denver
Abstract Number: 571 Working Group: Urban Aerosols
Abstract Here, we introduce the Platte River Photochemical Experiment, a sampling campaign aimed at understanding organic carbon and trace element photochemical interactions. We present the sample design, total metals, and soluble metals acquired from the winter campaign. In this study, Fe is of particular importance because, annually, 56.6 Tg of Fe enter the atmosphere, more than any other transition metal. Atmospheric particles also contain red-ox and photo-active organic species which may contribute to the solubilization of Fe. Fe collected in urban regions ranges from 22-50% soluble, compared to 0.2-1% the wind-blown desert dust. The origin of the elevated soluble Fe in urban areas is currently unclear. Two hypotheses are 1) soluble Fe is formed directly from urban sources or 2) chemical reactions during dust transport increases iron solubility. As Fe-containing dust travels through urban airsheds, it mixes with organic carbon and also has the potential for photochemistry. It has been demonstrated from lab procedures that, when exposed to sunlight and organic substances (e.g., PAH), Fe solubility can increase up to 10 fold. The likely mechanism for this process is via photo-Fenton chemistry. In photo-Fenton reactions, Fe(III), water and UV light react to produce the more soluble Fe(II) and hydroxyl radicals. In this study, PM2.5 was collected at three sites along the Platte River in the high plains in Colorado to understand if Fe solubility is affected by different types of organic sources (crustal, urban, and a mixture). The water soluble extracts are irradiated under simulated sunlight and the changes in soluble Fe measured and compared to the changes and quantity of organic carbon. This study is one of the first in attempting to understand how water soluble organic carbon affects the water solubility of trace elements.