Polyurethane Foam (PUF) Disk Samplers for Measuring Trace Metals in Ambient Air

A new method is presented for measuring atmospheric concentrations of trace metals in airborne particulate matter using polyurethane foam (PUF) disk passive air samplers (PUF-PASs) and passive dry deposition air samplers (PAS-DDs), which until now have mainly been used to assess organic pollutants in air. A field calibration study was conducted at one of the sites where measurements of trace metals were available using conventional methods. Uptake profiles of PUF-PASs and PAS-DDs were linear over the full 56 days that the samplers were deployed. The results confirm the ability of both passive sampler types to provide time-integrated measurements of airborne trace metals. For the PUF-PAS, the derived sampling rates (R) were generally in the range of default values derived for organic pollutants (i.e., 4 ± 2 m³/day). For the PAS-DD, the collection of the larger depositing particles resulted in elevated effective sampling rates, which were up to ∼4 times higher than for the PUF-PAS. Sampling rates for the PAS-DD were more variable compared to those for the PUF-PAS, probably due to the variability of the association of various trace metals with larger particles. Results from the PAS-DD were also converted to effective dry deposition fluxes and were as high as 6700 μg m^–2 day^–1 for iron. This study provides a proof concept and methodology for the application of PUF disk-based samplers as a versatile and cost-effective tool for studying trace metals, in addition to organics, in ambient air. The method was used to assess concentrations of 25 trace metals in ambient using PUF-PASs deployed across six urban sites in the greater Toronto area, impacted by different emission sources to air. The highest trace metal concentrations were measured at sites impacted by traffic.