Quantification of major particulate matter species from a single filter type using infrared spectroscopy – application to a large-scale monitoring network

Abstract

Abstract. To enable chemical speciation, monitoring networks collect particulate matter (PM) on different filter media, each subjected to one or more analytical techniques to quantify PM composition present in the atmosphere. In this work, we propose an alternate approach that uses one filter type (teflon or polytetrafluoroethylene, PTFE, commonly used for aerosol sampling) and one analytical method, Fourier transform infrared (FT-IR) spectroscopy to measure almost all of the major constituents in the aerosol. In the proposed method, measurements using the typical multi-filter, multi-analytical techniques are retained at a limited number of sites and used as calibration standards. At all remaining sites, only sampling on PTFE and analysis by FT-IR is performed. This method takes advantage of the sensitivity of the mid-IR domain to various organic and inorganic functional groups and offers a fast and inexpensive way of exploring sample composition. As a proof of concept, multiple years of samples collected within the Interagency Monitoring of PROtected Visual Environment network (IMPROVE) are explored with the aim of retaining high quality predictions for a broad range of atmospheric compounds including mass, organic (OC), elemental (EC), and total (TC) carbon, sulfate, nitrate, and crustal elements. Findings suggest that models based on only 21 sites, covering spatial and seasonal trends in atmospheric composition, are stable over a 3 year period within the IMPROVE network with acceptable prediction accuracy (R2 > 0.9, median bias less than 3 %) for most constituents. The major limitation is measuring nitrate as it is known to volatilize off of PTFE filters. Incorporating additional sites at low cost, partially replacing existing, more time- and cost-intensive techniques, or using the FT-IR data for quality control or substitute for missing data, are among the potential benefits of the one-filter, one-method approach.

Stability assessment of organic sulfur and organosulfate compounds in filter samples for quantification by Fourier Transform-Infrared Spectroscopy

“…PTFE filters are stored at room temperature and analyzed between 3 and 12 months after collection (typically 6 to 9 months) for PM mass, elements and filter-based light absorption. Recently, FT-IR analysis, a non-destructive method, has been performed on IMPROVE samples to reproduce routinely measured compositional data (Debus et al, 2022) and measure the functional group composition of the organic fraction (Ruthenburg et al, 2014). FT-IR analysis has also been conducted on other networks and in chamber and field studies to measure organic functional groups (Boris et al, 2021(Boris et al, , 2019Laurent and Allen, 2004;Russell et al, 2011;Ruthenburg et al, 2014;Yazdani et al, 2022).…”