Source apportionment of trace elements and black carbon in an urban industrial area (Portland, Oregon)

Abstract

This paper reports a current source apportionment study of trace elements and black carbon in particulate matter in industrial Southeast Portland, Oregon. The study aimed to determine whether metal pollution hotspots identified in the area in 2016 had been successfully mitigated by baghouse installation, or whether industrial sources continued to dominate local particulate matter. Particulate matter was filter-collected nearly continuously in 24-hour intervals between October 2017 and March 2018 (101 total filters). Filters were analyzed for 30 elements by x-ray fluorescence; black carbon was measured continuously during filter sampling using an aethalometer. EPA's Positive Matrix Factorization 5.0 was used for source apportionment modeling, yielding a 5-factor optimal solution. The source identities were resolved to be diesel and fuel emissions, sea salt, soil dust, secondary sulfates, and metals industry. The metals industry source was much less significant than expected, suggesting effective emissions reductions from the local factory. The source profiles' correlation with wind direction and speed using bivariate polar plots was examined to give further insight into the source identities and their locations. The NOAA HYSPLIT model was also used for air flow back-trajectory analysis. The results of the HYSPLIT and bivariate polar plots suggest that the coal power plant in eastern Oregon is a significant source of sulfates and mercury emissions. Using PMF on particulate matter data from a second industrial location in Southeast Portland (98 filters) revealed the same major sources except for the metals industry source, supporting the conclusion that regional sources dominate particulate matter metals composition, despite measurements made in an industrial urban location.