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Ozonolysis of model nitrogen-containing alkenes shows a wide range of reactivity and formation of toxic products. 

The neonicotinoid nitenpyram (NPM) is a multifunctional nitroenamine [(R₁N)(R₂N)C=CHNO₂] pesticide. As a nitroalkene, it is structurally similar to other emerging contaminants such as the pharmaceuticals ranitidine and nizatidine. Because ozone is a common atmospheric oxidant, such compounds may be oxidized on contact with air to form new products that have different toxicity compared to the parent compounds. Here we show that oxidation of thin solid films of NPM by gas-phase ozone produces unexpected products, the majority of which do not contain oxygen, despite the highly oxidizing reactant. A further surprising finding is the formation of gas-phase nitrous acid (HONO), a species known to be a major photolytic source of the highly reactive hydroxyl radical in air. The results of application of a kinetic multilayer model show that reaction was not restricted to the surface layers but, at sufficiently high ozone concentrations, occurred throughout the film. The rate constant derived for the O₃−NPM reaction is 1 × 10⁻¹⁸cm³⋅s⁻¹, and the diffusion coefficient of ozone in the thin film is 9 × 10⁻¹⁰cm²⋅s⁻¹. These findings highlight the unique chemistry of multifunctional nitroenamines and demonstrate that known chemical mechanisms for individual moieties in such compounds cannot be extrapolated from simple alkenes. This is critical for guiding assessments of the environmental fates and impacts of pesticides and pharmaceuticals, and for providing guidance in designing better future alternatives.

 

While atmospheric particles affect health, visibility and climate, the details governing their formation and growth are poorly understood on a molecular level. A simple model system for understanding the interactions between the gas and particle phases is the reaction of bases with acids, both of which are common constituents of atmospheric particles. In the present study, uptake coefficients for the reactions of gas phase ammonia, methylamine, ethylamine, dimethylamine and trimethylamine with a series of solid dicarboxylic acids (diacids) were measured at 296 ± 1 K using a Knudsen cell interfaced to a quadrupole mass spectrometer. The uptake coefficients ( γ ) for a given amine follow an odd–even trend in carbon number of the diacid, and are larger for the odd carbon diacids. Values range from γ = 0.4 for ethylamine on malonic acid (C3) to less than ∼10 −6 for ammonia and all amines on adipic (C6) and pimelic (C7) acids. Basicity or structure of the amines/ammonia alone do not explain the effect of the base on uptake. The crystal structures of the diacids also play a key role, which is especially evident for malonic acid (C3). Evaporation of aqueous mixtures of amines/ammonia with odd carbon diacids show the formation of ionic liquids (ILs) or in some cases, metastable ILs that revert back to a stable solid salt upon complete evaporation of water. The trends with amine and diacid structure provide insight into the mechanisms of uptake and molecular interactions that control it, including the formation of ionic liquid layers in some cases. The diversity in the kinetics and mechanisms involved in this relatively simple model system illustrate the challenges in accurately representing such processes in atmospheric models.