Concentration and source origin of lanthanoids in the Canadian atmospheric particulate matter: a case study

Ambient PM2.5 and PM2.5–10 samples collected at selected urban and rural sites within the Canadian National Air Pollution Surveillance (NAPS) PM2.5 Speciation Program were analyzed for lanthanoids and other elements. The average concentrations of total lanthanoids (calculated as sum of concentrations of all elements) in PM2.5 ranged from 0.059 to 0.334 ng m−3. These concentrations were two times lower than in PM2.5–10 samples and generally lower than values reported for industrial and urban areas around the world. The highest concentrations of lanthanoids were found in PM2.5 samples collected at the Halifax NS site, located near a petroleum refining complex. In addition, La/Ce and La/Sm ratios at this site were significantly higher than their natural values. Increased La–enrichment factors were also found in Wallaceburg ON, which is located in a rural area, about 50 km downwind of two major petrochemical complexes. The results of this study demonstrate that La–enrichment factors are reliable tracers of emissions from oil refining industry.