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

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 while sampling on PTFE and analysis by FT-IR is solely performed at the remaining locations. This method takes advantage of the sensitivity on 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 total 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 three year period within the IMPROVE network with prediction accuracy (R2 > 0.9, median bias less than 3 % for most constituents. Incorporating additional sites at low cost or partially replacing existing, more time and cost intensive techniques are among the potential benefits of one-filter, one-method approach.