AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
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High Time-Resolution Measurements of Ambient Metals and Elements in Los Angeles: Source Apportionment and Temporal Variations
SINA HASHEMINASSAB, Payam Pakbin, Andrea Polidori, Aaron Katzenstein, Jason Low, South Coast Air Quality Management District
Abstract Number: 502 Working Group: Source Apportionment
Abstract The Los Angeles Basin is home to some communities that encompass several metal-processing facilities in close proximity to each other and to residential neighborhoods. In 2016, the South Coast Air Quality Management District initiated an extensive investigative air monitoring campaign to identify and address sources of hexavalent chromium (Cr6+) and other toxic metals in the City of Paramount. Using portable air samplers, 24-hr time-integrated filter samples were collected every third day at a total of 48 different locations throughout the City for toxic metals analysis. Highly elevated levels of Cr6+ were found initially and additional efforts were conducted to better characterize sources of Cr6+ and other metals that were be impacting nearby communities. As part of these efforts, hourly concentrations of several metals were measured continuously with Xact 625 (Cooper Environmental Services, OR, USA) at two locations. This air monitoring campaign has been ongoing since 2016.
Air monitoring results indicated a substantial reduction in ambient levels of Cr6+ over time. This was achieved through rule amendments, enforcement actions, and voluntary emissions mitigation. Xact measurements provided useful information on the temporal trends of metals including their diurnal, day-of-week, and seasonal variations. The high time-resolution measurements also enabled investigating the impact of exceptional events (e.g., 4th of July fireworks) on the levels of ambient metals. A Positive Matrix Factorization (PMF) source apportionment model on the Xact data identified four source categories (i.e. soil/road dust, industrial emissions, vehicular abrasion, and residential wood smoke) with distinct profiles and temporal variations. Moreover, Conditional Probability Functions (CPFs) were computed using hourly wind data for individual species and PMF-derived source categories to identify the local source directions.