Response to O'Reilly et al. (2014)

Key Points O'Reilly et al. (2013) made several errors in their paper regarding environmental forensic techniques for pyrogenic polycyclic aromatic hydrocarbons (PAHs). Their use of alkylated PAHs in forensic evaluations to determine petrogenic (i.e., oil‐based) sources of PAHs is limited for urban sediments that are frequently classified as pyrogenic (i.e., combustion sources). O'Reilly et al. (2013) used a small number of samples from multiple sources in their principal components analysis figures and they simply do not have enough data to use this statistical technique. The authors recommended using both the USEPA's chemical mass balance and Unmix models for evaluating the source apportionment of PAHs in sediment data sets; however, this will not be feasible for most studies because the Unmix model requires a large sample size.