Fe(III)−oxalate complexes are likely abundant in clouds, fogs and aerosol water. They are photoreactive and can act as an important source of reactive oxygen species ( • OH, H 2 O 2 and HO 2 •) in tropospheric aqueous phases. Although the mechanisms involved in ferrioxalate photolysis have been investigated extensively, few kinetic and mechanistic information is available on the aging of dissolved organic compounds by this photochemical system. In this work, the Fe(III)−oxalate mediated photooxidation of guaiacol (GUA), a model for phenolic compounds emitted from biomass burning, was investigated under typical pH conditions of the atmospheric water. The effect of Fe(III) concentration, oxalate concentration and pH on the photooxidation of GUA was studied in detail. Our results revealed that oxalate can inhibit the oxidation of GUA by Fe(III) under the dark condition. However, the iron-catalyzed photooxidation of GUA can be strongly promoted in the presence of oxalate due to the formation of photoactive Fe(III)−oxalate complexes. GUA was rapidly oxidized to form a number of polymeric, functionalized and open-ring products with low volatility. Detailed reaction pathways for the photooxidation of GUA by Fe(III)−oxalate complexes were proposed based on the results of high-resolution mass spectrometry. This work suggests that ferrioxalate photochemistry can play an important role in the transformation of dissolved organics in atmospheric aqueous phases.

Atmospheric nitroaromatic compounds (NACs) are a class of aromatic species with both hydroxyl (−OH) and nitro groups (−NO 2 ) connecting to a benzene ring. They not only are important atmospheric pollutants that have proved to be genotoxic and phytotoxic (

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Organosulfates (OSs) have recently been observed to be a potentially important constituent of secondary organic aerosol (SOA); however, their molecular characterization in highly polluted atmospheres has not been probed in detail. This study thoroughly presents the characterization of OSs in polluted air and demonstrates their seasonal and diurnal variations, formation mechanisms, and contributions to organic aerosol. Atmospheric PM 2.5 samples were collected from an urban Shanghai site across the winter and summer of 2017. OSs were characterized by ultra-high-performance liquid chromatography (UHPLC) coupled with Orbitrap mass spectrometry (MS). Based on exact mass formulae in conjunction with previous chamber studies, hundreds of sulfur-containing compounds were tentatively identified as OSs. The number and abundance of OSs increased significantly during pollution episodes. The OSs in the clean aerosol samples were dominant in biogenic products, whereas the OSs in the polluted winter samples had distinctive anthropogenic characteristics. Aromatics and long-chain alkanes from anthropogenic emissions might be their precursors. By using synthesized standards, the total concentrations of 14 quantified OSs ranged 21.6-161 ng m −3 in summer and 5.85-84.3 ng m −3 in winter, respectively. Among these OSs, glycolic acid sulfate was the most abundant species (1.13-122 ng m −3 ). Further analysis of their seasonal and diurnal variations suggests possible contributions from multiple formation mechanisms, including acid-catalyzed and NO 3 -initiated oxidation reactions. Our results highlight that increased anthropogenic pollutant emissions (e.g., NO x and SO 2 ) can significantly enhance the SOA burden in biogenically influenced urban areas.