biostudies-literatureJaoui MIntramural EPAUS Environmental Protection Agency145592https://www.ebi.ac.uk/biostudies/studies/S-EPMC8363757biostudies-literatureUnknown775Recently, we identified seven novel hydroxy-carboxylic acids resulting from gas-phase reactions of isoprene in the presence of nitrogen oxides (NO_x), ozone (O₃), and/or hydroxyl radicals (OH). In the present study, we provide evidence that hydroxy-carboxylic acids, namely methyltartaric acids (MTA) are: (1) reliable isoprene tracers, (2) likely produced via rapid peroxy radical hydrogen atom (H) shift reactions (autoxidation mechanism) and analogous alkoxy radical H shifts in low and high NO_x environments respectively and (3) representative of aged ambient aerosol in the low NO_x regime. Firstly, MTA are reliable tracers of isoprene aerosol because they have been identified in numerous chamber experiments involving isoprene conducted under a wide The Science of the total environmentRapid production of highly oxidized molecules in isoprene aerosol via peroxy and alkoxy radical isomerization pathways in low and high NO<sub>x</sub> environments: Combined laboratory, computational and field studies.PMC8363757EPA999999Kleindienst TESzmigielski RLewandowski MPiletic IRRiedel TPJaoui MRudzinski KJfalseRapid production of highly oxidized molecules in isoprene aerosol via peroxy and alkoxy radical isomerization pathways in low and high NO<sub>x</sub> environments: Combined laboratory, computational and field studies.Recently, we identified seven novel hydroxy-carboxylic acids resulting from gas-phase reactions of isoprene in the presence of nitrogen oxides (NO_x), ozone (O₃), and/or hydroxyl radicals (OH). In the present study, we provide evidence that hydroxy-carboxylic acids, namely methyltartaric acids (MTA) are: (1) reliable isoprene tracers, (2) likely produced via rapid peroxy radical hydrogen atom (H) shift reactions (autoxidation mechanism) and analogous alkoxy radical H shifts in low and high NO_x environments respectively and (3) representative of aged ambient aerosol in the low NO_x regime. Firstly, MTA are reliable tracers of isoprene aerosol because they have been identified in numerous chamber experiments involving isoprene conducted under a wide 2021-01-01T00:00:00Z2021 Jun2026-05-09T03:20:04.539Z2025-02-19T02:58:41.342ZS-EPMC83637573438060810.1016/j.scitotenv.2021.145592