## 2 Materials and Methods
The multimode injector with TSP was operated in a 25:1 split mode, and the temperature was ramped from 50 to 450 \({}^{\circ}\)C at a rate of 900 \({}^{\circ}\)C/min. The final temperature was held constant for 3 min, and then decreased to 250 \({}^{\circ}\)C at a rate of 50 \({}^{\circ}\)C/min and held at 250 \({}^{\circ}\)C for the remainder of the run. For the gas chromatographic separation, two Agilent HP-5 MS ultra-inert fused silica columns (15 m \(\times\) 0.25 mm i.d., 0.25 \(\upmu\)m film thickness) separated by a midpoint backflush assembly were used. Ultra-high purity helium carrier gas was used with a constant flow of 1.2 mL/min on the front column (inlet to midpoint backflush assembly) and 1.3 mL/min on second column (midpoint backflush assembly to the MS transfer line). The GC oven was programmed to ramp from 40 \({}^{\circ}\)C to 200 \({}^{\circ}\)C at 10 \({}^{\circ}\)C/min and 200 \({}^{\circ}\)C to 310 \({}^{\circ}\)C at 6 \({}^{\circ}\)C/min, with a hold time of 20 min (54.33 min of total run time). The GC was interfaced to an Agilent 5977B single quadrupole mass selective detector. The MS transfer line temperature was 280 \({}^{\circ}\)C; the MS ion source was held at 280 \({}^{\circ}\)C and the MS quadrupole at 150 \({}^{\circ}\)C. The MS was operated in E.I. positive mode (70 eV) and set to scan from 45 to 550 amu (5-25 min), 50-750 amu (25-30 min), and 50-800 amu (30 min-end run). Methyl derivatives of the samples were formed in situ in the TSP using tetramethylammonium hydroxide (TMAH, 2.5% in methanol, Sigma-Aldrich, St. Louis, MO, USA). All GC/MS data were analyzed using a version of ESCAPE (Expert System for Characterization using AMDIS Plus Excel) developed specifically for Py-GC/MS of synthetic paint media [18,19]. Briefly, the total ion chromatogram (TIC) for a sample was analyzed by AMDIS (Automated Mass spectral Deconvolution and Identification System, version 2.73, NIST, Gaithersburg, MD, USA) to identify synthetic paint media marker compounds based on both mass spectral library matching and retention index. This information was output as an AMDIS report, which was then pasted into the Synthetic ESCAPE Excel report template (Excel version 2402). The template uses formulas to automatically sort and sum areas of the marker compounds and produce graphs and tables associated with the major classes of synthetic paint media: oil/alkyl, acrylics, epoxy, urethane, and vinyl. A manuscript providing the full description of Synthetic ESCAPE and its application to the analysis of synthetic paint media is in preparation for publication. Images of the ultraviolet-light-induced visible fluorescence of the used Evolon sheets were taken using a PhaseOne XF, equipped with a IQ3 100 mega-pixel digital back (PhaseOne, Copenhagen, Denmark) and a Schneider Kreuznach 80 mm LS Blue Ring f/2.8 AF lens (Bad Kreuznach, Germany). The lens was fitted with a B + W 484 (Scheider Kreuznach, Bad Kreuznach, Germany) and a Tiffen 2E filter (Hauppauge, NY, USA) to ensure only light of 420-700 nm is captured. The camera was set to ISO 100 with a f/12 aperture. UV illumination was provided by two UV Systems (Renton, WA, USA) having TripleBright II lamps with over-lamp Hoya U-325C filters (Milpitas, CA, USA) to block visible light above 420 nm. RAW image captures included the UV InnovationsTM Target-UVTM (UV InnovationsTM, [[https://www.uvinnovations.com/](https://www.uvinnovations.com/)]([https://www.uvinnovations.com/](https://www.uvinnovations.com/)), Fremont, CA, USA); the images were white-balanced following the published UV InnovationsTM standards for the processing of 'low' fluorescent materials [20] and then saved as Tiff files.