Many studies have linked increased concentrations of airborne red-ox active metals, such as chromium, manganese, and iron, to subway systems. These higher concentrations have been linked to potential health risks to personnel who operate or almost exclusively ride the subway. Very few studies have been performed examining the effects of ground-level, outdoor light rail transit systems. The current study focused on the light rail system in Denver, Colorado.  Size-segregated air samples were collected using Sioutas personal cascade impactor samplers (PCIS) at three locations around downtown Denver:  on board the trains, at the side of the tracks, and at a background location in downtown Denver. Samples were collected onboard all five lines each day. Outside samples were collected for 42 hours a week while onboard samples were collected 36 hours a week. Four sets of samples were collected from January 24 to February 16, 2012. Results suggest that higher metal concentrations (especially steel components) are found near and onboard the train. Soluble iron was determined to be present mostly as Fe(II). While these levels may not be as high as in subways, metal concentrations could still pose serious health risks. Results from this study showed highest crustal enrichment factors of metals in samples collected on board the train, despite lower concentrations of total PM<sub>2.5</sub>. Fe in the PM<sub>2.5 </sub>at track-side and on board the trains was above the background by a factor of 1.89 and 1.54, respectively.  For Mn, the ratios were 1.34 for the track-side and 0.94 for the on board samples. Cr and Ni exhibited higher ratios over the back ground only in samples collected on board the trains at 1.59 (Cr) and 1.26 (Ni). Soluble metals were measured with Ni (53-71%), Cu (52-81%), and Zn (30-81%) exhibiting the highest solubilities across the different sites.  Soluble Fe ranged from 8-15% for the total measured Fe, indicating a non-crustal source of Fe.  Soluble Fe was also characterized as Fe(II) and Fe(III) with 87-90% of the soluble Fe being Fe(II).

Metal concentrations and soluble iron speciation in fine particulate matter from light rail activity in the Denver-Metropolitan area

249th National Meeting (2015)

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