Solid Waste Burning: An Overlooked Atmospheric Source of p -Phenylenediamine Antioxidants and Their Quinones

Abstract N,N′-Disubstituted p-phenylenediamines (PPDs) and their oxidized derivatives (PPD-Qs) are widely used as rubber antioxidants, but their atmospheric sources remain incompletely characterized. Here we systematically investigate solid waste burning as a previously overlooked source of atmospheric PPDs and PPD-Qs. Field measurements of uncontrolled open burning and controlled incineration, combined with suspect screening and targeted analysis, revealed distinct emission profiles. Suspect screening detected and annotated 47 PPD-related features (20 confirmed, five tentatively identified, and 22 provisionally annotated), with more features detected in open burning PM2.5 (n = 43) than in incineration PM2.5 (n = 27). Quantitative analysis showed that open burning predominantly emitted parent PPDs at higher concentrations (median: 11.54 μg/g PM2.5), whereas incineration was characterized by a higher relative abundance of PPD-Qs (median: 2.50 μg/g PM2.5). In a screening-level esimate for China, open burning accounted for more than 99.7% of the estimated emissions of the 10 targeted ∑(PPDs + PPD-Qs) from solid waste burning in China. These findings suggest that solid waste burning is an overlooked source of atmospheric PPDs and PPD-Qs, indicating the need to incorporate waste disposal into emission inventories and targeted emission control strategies.