The burden of N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) and its oxidized products on human health can no longer be ignored due to the detection types and concentrations in the environment continue to increase. Environmental ozone (O 3 ) and ultraviolet A (UVA) may induce ozonation and photoaging of 6PPD to produce toxic products. However, the impact of specific environmental conditions on the aging and toxic effects of 6PPD is unclear. This study investigated the aging effects of O 3 and UVA on 6PPD, and compared the repeated inhalation toxicity of differently aging 6PPDs in C57BL/6 male mice. The result showed that UVA and O 3 accelerated 6PPD aging, and the aging products varied depending on the O 3 and irradiation conditions. After 10 weeks of inhalation intoxication at human comparable level, mice exhibited significant neurobehavior alterations, respiratory dysfunction, and DNA damage in the blood, showing significant heterogeneity among groups. Notably, 6PPD treated with perozonation and UVA aging may be the most toxic. The study suggests inhalation health risks of transportation derived tire pollutants under the influence of ground-level ozone and ultraviolet light need more attention, and provides new insights into risk assessment and pollution control of 6PPD and other pollutants from the perspective of environmental factors.
Accurately measuring the pH of atmospheric aerosols is a prerequisite for understanding the multiphase chemistry that profoundly affects the environment and climate systems. Despite the advancements of experimental techniques for in situ pH measurements in aerosols, current studies are limited to measuring the static pH of aerosol microdroplets with an unperturbed composition. This steady-state scenario, however, deviates from the real-world aerosols undergoing atmospheric aging reactions, specifically, those characterized with a spontaneous displacement of strong bases (or acids) with high volatility. Here, we introduce a continuous and in situ measurement of aerosol pH by using a 4-mercaptopyridine-functionalized silver nanoparticle probe and surface-enhanced Raman spectroscopy. We find that the ammonium depletion─a spontaneous displacement of ammonium by dicarboxylic acid salts─continuously acidifies aerosol water over time. The decaying trends of pH in the aerosols under various humidity conditions can be unified with a universal exponential function. Such an exponentially decaying function further indicates that the ammonium depletion reaction is a self-limiting process. Our technique can be applied to study the dynamic change of aerosol acidity during the complex atmospheric aging processes, toward elucidating their implications on atmospheric chloride, nitrate, and ammonium cycles.
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