Contrasting the elemental composition of fine particulate matter in urban and remote samples using single particle inductively coupled plasma time-of-flight mass spectrometry (SP ICP-ToF-MS)

Elevated concentrations of particulate matter (PM) are associated with poor air quality, and the health effects of PM exposure depend, in part, on its elemental composition. However, techniques to measure the elemental composition of fine and ultrafine PM at the single particle level are limited in terms of their ability to quantitatively detect a wide range of elements in a single particle. In this work, PM2.5 was collected and extracted from polycarbonate filtration membranes using four different methods to optimize recoveries. Based upon gravimetry, the best method tested gave an extraction efficiency of 73 ± 18%. The elemental compositions of the extracted particles were then determined using single particle inductively coupled plasma time-of-flight mass spectrometry (SP ICP-ToF-MS), which was applied to compare the composition of urban PM (Montreal, Canada) and PM collected from a remote high latitude region impacted by local mineral dust (Dhal Tʼàʼ, Canada). With respect to particle number, greater quantities of trace elements associated with anthropogenic sources were observed at the urban site. Specifically, Cr, Pb, Ni, Zn, Ag or Cu were found in 3.8% of the urban particles, often at high mole percentages, but only in 0.7% of the remote particles. Furthermore, the distribution of single particle Fe:Ni and Fe:Cu ratios observed at the urban site was shifted to lower values relative to the remote site. The results demonstrate the value of SP ICP-ToF-MS for analyzing ambient PM, although improved recoveries and sampling methodologies are needed to unlock the full potential of this technique.