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Emerging contaminants (EC) distributed on surfaces in the environment can be oxidized by gas phase species (top–down) or by oxidants generated by the underlying substrate (bottom–up). One class of EC is the neonicotinoid (NN) pesticides that are widely distributed in air, water, and on plant and soil surfaces as well as on airborne dust and building materials. This study investigates the OH oxidation of the systemic NN pesticide acetamiprid (ACM) at room temperature. ACM on particles and as thin films on solid substrates were oxidized by OH radicals either from the gas phase or from an underlying TiO₂or NaNO₂substrate, and for comparison, in the aqueous phase. The site of OH attack is both the secondary >CH₂group as well as the primary –CH₃group attached to the tertiary amine nitrogen, with the latter dominating. In the case of top–down oxidation of ACM by gas phase OH radicals, addition to the –CN group also occurs. Major products are carbonyls and alcohols, but in the presence of sufficient water, their hydrolyzed products dominate. Kinetics measurements show ACM is more reactive toward gas phase OH radicals than other NN nitroguanidines, with an atmospheric lifetime of a few days. Bottom–up oxidation of ACM on TiO₂exposed to sunlight outdoors (temperatures were above 30 °C) was also shown to occur and is likely to be competitive with top–down oxidation. These findings highlight the different potential oxidation processes for EC and provide key data for assessing their environmental fates and toxicologies. 

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

Abstract We investigated the photosensitizing properties of secondary organic aerosol (SOA) formed during the hydroxyl radical (OH) initiated oxidation of naphthalene. This SOA was injected into an aerosol flow tube and exposed to UV radiation and gaseous volatile organic compounds or sulfur dioxide (SO₂). The aerosol particles were observed to grow in size by photosensitized uptake of d‐limonene and β‐pinene. In the presence of SO₂, a photosensitized production (0.2–0.3 µg m⁻³ h⁻¹) of sulfate was observed at all relative humidity (RH) levels. Some sulfate also formed on particles in the dark, probably due to the presence of organic peroxides. The dark and photochemical pathways exhibited different trends with RH, unraveling different contributions from bulk and surface chemistry. As naphthalene and other polycyclic aromatics are important SOA precursors in the urban and suburban areas, these dark and photosensitized reactions are likely to play an important role in sulfate and SOA formation.