Sanghyun Ryoo (Department of Chemistry, Kyungpook National University, Daegu, 41566, Republic of Korea)

Sunghwan Kim (Department of Chemistry, Kyungpook National University, Daegu, 41566, Republic of Korea)

Sanghyun Ryoo (Department of Chemistry, Kyungpook National University, Daegu, 41566, Republic of Korea)

Taehyeon Kim (School of Architecture, Civil, Environmental, and Energy Engineering, Kyungpook National University, Daegu, 41566, Republic of Korea)

Ho-Jin Lim (School of Architecture, Civil, Environmental, and Energy Engineering, Kyungpook National University, Daegu, 41566, Republic of Korea)

Sunghwan Kim (Department of Chemistry, Kyungpook National University, Daegu, 41566, Republic of Korea)

N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD), a tire antioxidant, forms the highly toxic 6PPD-quinone (6PPD-Q) through atmospheric oxidation. However, oxidation products of related PPD antioxidants (CPPD, IPPD, and DPPD) and benzothiazole-related compounds (MBT and OTH) remain poorly characterized. To support future analysis of these additives and their products in urban PM2.5, each compound was exposed to gas-phase O3 (4,800 ppb, 60 min) or OH radicals in a flow reactor, simulating approximately 7 days of atmospheric aging. Products were screened by liquid chromatography-high-resolution mass spectrometry (LC-HRMS), and the six parent compounds were analyzed in PM2.5. Forty-five transformation-product candidates were prioritized. 6PPD-Q was observed under both oxidation conditions. IPPD yielded the greatest diversity of TP candidates, including an IPPD-quinone candidate (C15H16N2O2). Candidates matching the molecular formulas of CPPD-quinone and DPPD-quinone were also observed, but were considered tentative because MS/MS data were unavailable. In PM2.5, 6PPD, CPPD, IPPD, and OTH were detected, whereas DPPD and MBT were not. These results extend oxidation-product screening beyond 6PPD and provide a basis for monitoring tire-derived chemicals in urban air.​