Using PM2.5 lanthanoid elements and nonparametric wind regression to track petroleum refinery FCC emissions

A long term air quality study is being conducted in Roxana, Illinois, USA, at the fenceline of a petroleum refinery. Measurements include 1-in-6 day 24-hour integrated ambient fine particulate matter (PM2.5) speciation following the Chemical Speciation Network (CSN) sampling and analysis protocols. Lanthanoid elements, some of which are tracers of fluidized-bed catalytic cracker (FCC) emissions, are also measured by inductively coupled plasma-mass spectrometry (ICP-MS) after extraction from PM2.5 using hot block-assisted acid digestion. Lanthanoid recoveries of 80-90% were obtained for two ambient particulate matter standard reference materials (NIST SRM 1648a and 2783). Ambient PM2.5 La patterns could be explained by a two-source model representing resuspended soil and FCC emissions with enhanced La/Ce ratios when impacted by the refinery. Nonparametric wind regression demonstrates that when the monitoring station was upwind of the refinery the mean La/Ce ratio is consistent with soil and when the monitoring station is downwind of the refinery the mean ratio is more than four times higher for bearings that corresponds to maximum impacts. Source apportionment modeling using EPA UNMIX and EPA PMF could not reliably apportion PM2.5 mass to the FCC emissions. However, the weight of evidence is that such contributions are small with no large episodes observed for the 164 samples analyzed. This study demonstrates the applicability of a hot block-assisted digestion protocol for the extraction of lanthanoid elements as well as insights obtained from long-term monitoring data including wind direction-based analyses.