Daphne R. Patten*, Andrew E. Paulson, and Trevor T. Forsman | Iowa State University Abstract: Fingerprints are invaluable evidence in the criminal justice system because of their ability to identify individuals. The presenters introduced a simple kinetics model in the 2022 National Institute of Justice (NIJ) Forensic Science Research & Development Symposium using triacylglycerol (TG) standards based on the ozonolysis of TGs. Although this simple model revealed many important factors in TG aging, such as temperature and ozone concentration, there was some discrepancy with the aging of real fingerprint TGs. In the current study, an empirical model was developed based on aging real fingerprint samples in a controlled environment. The fingerprint samples include two sets: set #1 advanced aging (four individuals at 100 ppb ozone, 30°C, 0–8 hours) and set #2 ambient aging (one individual at 13 ppb, 20.6°C, 0–7 days). All samples were sprayed with 10 mM sodium acetate and sputtered with gold. Analysis was completed using a Q Exactive™ HF (Thermo Scientific™) equipped with a matrix-assisted laser desorption/ionization (MALDI) source (Spectroglyph, LLC) set to positive ion mode. The data were then analyzed using Xcalibur™ Qual Browser and Python (Thermo Scientific™). There are two most significant limitations in the previous simple kinetics model. First, the simple model ignores the difference in the ozonolysis decay rate resulting from varying levels of unsaturation in TGs. Second, it also ignores the difference between standard TGs and fingerprint TGs, such as the effect of other lipids, including wax esters and fatty acids. In the current study, the researchers empirically derive kinetics parameters to address the latter issue. Furthermore, they address the former issue by deriving kinetics parameters separately for mono-, di-, tri-, and tetra-unsaturated TGs. The advanced kinetics model derived from set #1 could predict the deposition time quite accurately for the midrange aging (4 hours, 30°C, 100 ppb) with 12% root mean square (RMS) error compared with 42% in the simple kinetics model. Though the empirical model best predicts midrange aging, early and late aging show higher relative errors of 45% and 38%, respectively, which are still much better than the 63% and 50% in the simple kinetics model. When the empirical model was applied to ambient aging set #2, it produced higher errors in the range of 29%–39%, probably because of insufficient temperature correction and ozone concentration measurement error. To conclude, the empirical model shows notable improvements to the time since deposition estimations and is applicable to ambient conditions found at crime scenes. Future studies will continue to further improve the kinetics model and test over wide environmental conditions.