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Abstract Sinking marine particles drive the biological pump that naturally sequesters carbon from the atmosphere. Despite their small size, the compartmentalized nature of particles promotes intense localized metabolic activity by their bacterial colonizers. Yet the mechanisms promoting the onset of denitrification, a metabolism that arises once oxygen is limiting, remain to be established. Here we show experimentally that slow sinking aggregates composed of marine diatoms—important primary producers for global carbon export—support active denitrification even among bulk oxygenated water typically thought to exclude anaerobic metabolisms. Denitrification occurs at anoxic microsites distributed throughout a particle and within microns of a particle’s boundary, and fluorescence-reporting bacteria show nitrite can be released into the water column due to segregated dissimilatory reduction of nitrate and nitrite. Examining intact and broken diatoms as organic sources, we show slowly leaking cells promote more bacterial growth, allow particles to have lower oxygen, and generally support greater denitrification. 

Anthropogenic organic carbon emissions reporting has been largely limited to subsets of chemically speciated volatile organic compounds. However, new aircraft-based measurements revealed total gas-phase organic carbon emissions that exceed oil sands industry–reported values by 1900% to over 6300%, the bulk of which was due to unaccounted-for intermediate-volatility and semivolatile organic compounds. Measured facility-wide emissions represented approximately 1% of extracted petroleum, resulting in total organic carbon emissions equivalent to that from all other sources across Canada combined. These real-world observations demonstrate total organic carbon measurements as a means of detecting unknown or underreported carbon emissions regardless of chemical features. Because reporting gaps may include hazardous, reactive, or secondary air pollutants, fully constraining the impact of anthropogenic emissions necessitates routine, comprehensive total organic carbon monitoring as an inherent check on mass closure. 

Peracetic acid (PAA) is being considered as a disinfectant in membrane-based wastewater reuse systems, but its compatibility with polyamide membranes has not been thoroughly investigated. In this work, we showed that PAA induced much less change in the performance and material characteristics of NF90 membranes than the traditional disinfectant free chlorine (NaOCl). The change in membrane water flux and the rejection of salt and neutral organic compounds after PAA exposure (1–180 g h L −1 ) is significantly less than that resulting from NaOCl exposure at levels as low as 1 g h L −1 . The presence of two wastewater constituents, chloride or Fe( ii ), did not significantly impact membrane performance upon exposure to PAA. Surface characterization showed that oxygen was incorporated into polyamide by PAA, some of which was attributed to the formation of carboxylic acid groups. Experiments using a model aromatic amide, benzanilide, indicated an unexpected role of PAA in protecting the membrane from radicals formed by Fe( ii ) and the H 2 O 2 present in commercial PAA formulations. Furthermore, product identification suggests that both amide bond breakage and ring oxidation are possible reaction mechanisms for PAA. Our findings support that PAA is a viable disinfectant candidate for wastewater reuse and warrants further evaluation. 

The gas-to-particle transition is a critical and hitherto poorly understood aspect in carbonaceous soot particle formation. Polycyclic Aromatic Hydrocarbons (PAHs) are key precursors of the solid phase, but their role has not been assessed quantitatively probably because, even if analytical techniques to quantify them are well developed, the challenge to adapt them to flame environments are longstanding. Here, we present simultaneous measurements of forty-eight gaseous species through gas capillary-sampling followed by chemical analysis and of particle properties by optical techniques. Taken together, they enabled us to follow quantitatively the transition from parent fuel molecule to PAHs and, eventually, soot. Importantly, the approach resolved spatially the structure of flames even in the presence of steep gradients and, in turn, allowed us to follow the molecular growth process in unprecedented detail. Noteworthy is the adaptation to a flame environment of a novel technique based on trapping semi-volatile compounds in a filter, followed by off-line extraction and preconcentration for quantitative chemical analyses of species at mole fractions as low as parts per billion. The technique allowed for the quantitation of PAHs containing up to 6 aromatic rings. The principal finding is that only one- and two-ring aromatic compounds can account for soot nucleation, and thus provide the rate-limiting step in the reactions leading to soot. This finding impacts the fundamental understanding of soot formation and eases the modeling of soot nucleation by narrowing the precursors that must be predicted accurately.